0001437749-23-008846 | 10-K | XBRL Viewer

Fair Value Disclosures [Text Block]

3. Fair Value of Financial Instruments

Fair Value of Financial Instruments

The Company determines the fair value of its financial instruments based on a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three levels:

Level 1 – Observable inputs such as quoted prices in active markets for an identical asset or liability that the Company has the ability to access as of the measurement date. Financial assets and liabilities utilizing Level 1 inputs include money market funds.

Level 2 – Inputs, other than quoted prices included within Level 1, which are directly observable for the asset or liability or indirectly observable through corroboration with observable market data. Financial assets and liabilities utilizing Level 2 inputs include commercial paper, corporate bonds and asset-backed securities.

Level 3 – Unobservable inputs in which there is little or no market data for the asset or liability which requires the reporting entity to develop its own assumptions. The Company did not classify any of its investments within Level 3 of the fair value hierarchy.

The following table sets forth the fair value of the Company’s financial assets measured on a recurring basis (in thousands):

		*December 31, 2022*
Assets	*Classification*	*Level 1*		*Level 2*		*Level 3*		*Total*
Money market funds	Cash and cash equivalents	$	57,973	$	—	$	—	$	57,973
Total assets measured at fair value		$	57,973	$	—	$	—	$	57,973

		*December 31, 2021*
Assets	*Classification*	*Level 1*		*Level 2*		*Level 3*		*Total*
Money market funds	Cash and cash equivalents	$	23,675	$	—	$	—	$	23,675
Total assets measured at fair value		$	23,675	$	—	$	—	$	23,675

During the years ended December 31, 2022 and 2021, the Company did not record impairment charges related to its marketable investments. During the years ended December 31, 2022 and 2021, the Company did not have any transfers between Level 1, Level 2 or Level 3 of the fair value hierarchy. Additionally, the Company did not have any financial assets and liabilities measured at fair value on a non-recurring basis as of December 31, 2022 or 2021.

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Note 11 - Income Taxes - Reconciliation of Provision for Income Taxes (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Federal tax at statutory rate	21.00%	21.00%	21.00%
State tax at statutory rate	8.40%	8.40%	8.40%
Research and development credits	0.90%	1.90%	2.10%
Change in valuation allowance	(18.40%)	(26.80%)	(43.30%)
Deferred adjustment	(5.30%)	0.00%	8.50%
Change in tax rate	0.00%	0.00%	4.20%
Uncertain Tax Position	(5.70%)	(2.30%)	0.00%
Other	(0.90%)	(2.20%)	(0.80%)
Provision for income taxes	0.00%	0.00%	0.00%

Note 15 - Employee Benefit Plans (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 0

Document And Entity Information - USD ($)	12 Months Ended
Document And Entity Information - USD ($)	Dec. 31, 2022	Mar. 27, 2023	Jun. 30, 2022
Document Information [Line Items]
Entity Central Index Key	0001625101
Entity Registrant Name	Pulse Biosciences, Inc.
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2022
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2022
Document Transition Report	false
Entity File Number	001-34899
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-5696597
Entity Address, Address Line One	3957 Point Eden Way
Entity Address, City or Town	Hayward
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94545
City Area Code	510
Local Phone Number	906-4600
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	PLSE
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float			$ 23,793,458
Entity Common Stock, Shares Outstanding		37,592,588
Auditor Firm ID	34
Auditor Name	Deloitte & Touche LLP
Auditor Location	San Jose, California

Note 6 - Stockholders' Equity and Stock-based Compensation

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Text Block]

6. Stockholders’ Equity and Stock-Based Compensation

Preferred Stock

The Company has authorized a total of 50,000,000 shares of preferred stock, par value $0.001 per share, none of which were outstanding at December 31, 2022 and 2021. The Company’s Board of Directors (the “Board”) has the authority to issue preferred stock and to determine the rights, preferences, privileges, and restrictions, including voting rights, without any further vote or action by the Company’s stockholders.

Common Stock

The Company has authorized a total of 500,000,000 shares of common stock, par value $0.001 per share.

Rights Offering

On June 9, 2022, the Company completed a rights offering (the “2022 Rights Offering") resulting in the sale of 7,317,072 units (the “Units”), at a price of $2.05 per Unit, with each Unit consisting of one share of the Company’s common stock, par value $0.001 per share, and one warrant (the “2022 Rights Offering Warrants”) to purchase one share of common stock. The common stock and warrants comprising the Units separated upon the closing of the 2022 Rights Offering and were issued individually. 7,317,072 shares of common stock and warrants to acquire up to an additional 7,317,072 shares of common stock were issued in the 2022 Rights Offering. The Company received aggregate gross proceeds from the 2022 Rights Offering of $15 million. If exercised, additional gross proceeds of up to $15 million may be received through the exercise of the 2022 Rights Offering Warrants. Each 2022 Rights Offering Warrant is exercisable for one share of the Company’s common stock at an exercise price equal to $2.05. The 2022 Rights Offering Warrants are exercisable immediately and expire on the fifth anniversary of the closing of the 2022 Rights Offering. The 2022 Rights Offering Warrants are subject to redemption by the Company for $0.01 per underlying share of common stock, on not less than 30 days written notice, if the volume weighted average price of the Company’s common stock equals or exceeds 200% of the exercise price for the warrants, subject to adjustment, per share, for 20 consecutive trading days, provided that the Company may not redeem the warrants prior to the date that is three months after the issuance date. Robert W. Duggan, the Company’s largest stockholder and Executive Chairman, purchased approximately 56% of the shares offered in the 2022 Rights Offering.

Private Placement Securities Purchase Agreement

On June 30, 2021, the Company entered into a Securities Purchase Agreement with Robert W. Duggan, the Company’s largest stockholder and Executive Chairman, pursuant to which the Company issued and sold to Mr. Duggan 3,048,780 shares of the Company’s common stock, par value $0.001 per share, in a private placement (the “Private Placement”), at a price per share of $16.40, which was the market closing price on the date of the transaction. These shares were paid for through (i) the conversion of $41.0 million aggregate principal amount, together with all accrued and unpaid interest outstanding, owed to Mr. Duggan under the Loan Agreement by and between the Company and Mr. Duggan (Note 13), and (ii) additional cash in the amount of approximately $8.4 million. Upon the closing of this Private Placement and satisfaction of the outstanding debt, the Loan Agreement terminated, without any early termination fees or penalties being owed by the Company, and no additional amounts were owed to Mr. Duggan under the Loan Agreement. The cash proceeds of approximately $8.4 million were received by the Company in July 2021.

At-the-Market Equity Offering

On February 4, 2021, the Company entered into a sales agreement (the “Sales Agreement”) with Stifel, Nicolaus & Company, Inc. (“Stifel”) as sales agent, pursuant to which the Company may offer and sell, from time to time, through Stifel, up to $60.0 million in shares of common stock, by any method permitted by law deemed to be an “at-the-market” offering as defined in Rule 415 promulgated under the Securities Act of 1933, as amended. The Company has no obligation to make any sales of its common stock pursuant to such Sales Agreement. During the year ended December 31, 2022, the Company did not issue or sell any shares of common stock under the Sales Agreement. During the year ended December 31, 2021 the Company issued and sold 288,490 shares of common stock under the Sales Agreement. The shares were sold at a weighted average price of $27.73 per share for aggregate net proceeds of approximately $7.4 million, after deducting sales commissions and offering costs payable by the Company.

Common Stock Warrants

In connection with a private placement in November 2014 of the Company’s common stock, par value $0.001 per share, the Company issued warrants as compensation to the placement agent to purchase a total of 299,625 shares of its common stock at an exercise price of $2.67 per share (the “Private Placement Warrants”). The Private Placement Warrants were exercisable for a period of seven years from issuance. In March 2021, warrants to purchase 45,638 shares of common stock were net exercised, resulting in the issuance of 40,563 shares of common stock. In November 2021, the last remaining 600 Private Placement Warrants expired unexercised, resulting in no further Private Placement Warrants outstanding.

In connection with the closing of the Company’s initial public offering in May 2016, the Company issued warrants as compensation to its underwriters, to purchase a total of 574,985 shares of its common stock at an exercise price of $5.00 per share (the “IPO Warrants”). The IPO Warrants were exercisable for a period of five years from issuance. In March 2021, warrants to purchase 85,385 shares of common stock were net exercised, resulting in the issuance of 68,958 shares of common stock. All IPO Warrants were exercised prior to their expiration in May 2021, resulting in no further IPO Warrants outstanding.

In connection with a June 2020 rights offering, the Company issued warrants (the “2020 Rights Offering Warrants”) to purchase a total of 641,571 shares of its common stock at an exercise price of $7.01. These 2020 Rights Offering Warrants were exercisable immediately and expired on the fifth anniversary of the completion of the Rights Offering, or June 16, 2025, subject to certain redemption rights by the Company. The 2020 Rights Offering Warrants were subject to redemption by the Company, on or after December 16, 2020, six months after the issuance date, for $0.01 per warrant, with not less than 30 days written notice, if the volume weighted average price of our common stock equaled or exceeded 200% of the exercise price for the 2020 Rights Offering Warrants for 10 consecutive trading days. On December 31, 2020, the Company met the requirements for redemption of these warrants and delivered a notice of redemption to redeem all of the outstanding warrants that remained unexercised at February 5, 2021, for the redemption price of $0.01 per warrant. Pursuant to the redemption, the Company redeemed 5,139 warrants. Prior to the February 5, 2021 redemption date, 636,432 warrants were exercised, generating approximately $4.5 million of total gross proceeds to the Company. As of December 31, 2022, there were no 2020 Rights Offering Warrants outstanding.

In connection with the 2022 Rights Offering, the Company issued 2022 Rights Offering Warrants to purchase a total of 7,317,072 shares of its common stock at an exercise price of $2.05. The 2022 Rights Offering Warrants are exercisable immediately and expire on the fifth anniversary of the closing of the 2022 Rights Offering. The 2022 Rights Offering Warrants are subject to redemption by the Company for $0.01 per underlying share of common stock, on not less than 30 days written notice, if the volume weighted average price of the Company’s common stock equals or exceeds 200% of the exercise price for the warrants, subject to adjustment, per share, for 20 consecutive trading days, provided that the Company may not redeem the warrants prior to the date that is three months after the issuance date. In the year ended December 31, 2022, a total of 13,240 warrants were exercised. As of December 31, 2022, there were 7,303,832 2022 Rights Offering Warrants outstanding.

A summary of total warrants activity for the year ended December 31, 2022 is presented below:

						*Weighted*
						*Average*
				*Weighted*		*Remaining*
	*Number of*			*Average*		*Contractual*
	*Shares*			*Exercise Price*		*Life (in Years)*
Warrants outstanding at December 31, 2021		—		$	—		—
Issued		7,317,072			2.05
Exercised		(13,240	)		2.05
Expired/Redeemed		—			—
Warrants outstanding and exercisable at December 31, 2022		7,303,832		$	2.05		4.43

Equity Plans

2017 Equity Incentive Plan and 2017 Inducement Equity Incentive Plan

The Board previously adopted, and the Company’s stockholders approved, the Company’s 2017 Equity Incentive Plan (the “2017 Plan”).

The 2017 Plan has a 10-year term, and provides for the grant of stock options, stock appreciation rights, restricted stock, RSUs, performance units, and performance shares to employees, directors and consultants of the Company and any parent or subsidiary of the Company, as the Compensation Committee of the Board may determine. Subject to an annual evergreen increase and adjustment in the case of certain capitalization events, the Company initially reserved 1,500,000 shares of the Company’s common stock for issuance pursuant to awards under the 2017 Plan. In addition, shares remaining available under the Company’s 2015 Equity Incentive Plan, as amended (the “2015 Plan”), and shares reserved but not issued pursuant to outstanding equity awards that expire or terminate without being exercised or that are forfeited or repurchased by the Company will be added to the shares of common stock available for issuance under the 2017 Plan. The 2017 Plan is administered by the Board’s Compensation Committee. Effective January 1, 2022 and 2021, the number of shares of common stock available under the 2017 Plan increased by 1,188,657 and 1,022,002 shares, respectively, pursuant to the evergreen provision of the 2017 Plan. Under the evergreen provision of the 2017 Plan, the share increase is determined based on the least of (i) 1,200,000 shares, (ii) 4% of the Company’s common stock outstanding at December 31 of the immediately preceding year, or (iii) such number of shares as determined by the Board. As of December 31, 2022, 2,368,716 shares of common stock remained available for issuance under the 2017 Plan.

During November 2017, the Board of the Company adopted the 2017 Inducement Equity Incentive Plan (the “Inducement Plan”) and reserved 1,000,000 shares of the Company’s common stock for issuance pursuant to equity awards granted under the Inducement Plan. The Inducement Plan was adopted without stockholder approval.

The Inducement Plan has a 10-year term and provides for the grant of equity-based awards, including non-statutory stock options, RSUs, restricted stock, stock appreciation rights, performance shares and performance units, and its terms are substantially similar to the 2017 Plan, including with respect to treatment of equity awards in the event of a “merger” or “change in control” as defined under the Inducement Plan. Options issued under the Inducement Plan may have a term up to ten years and have variable vesting provisions. New hire grants generally vest 25% per year starting upon the first anniversary of the grant. Equity-based awards issued under the Inducement Plan are only issuable to individuals not previously engaged as employees or non-employee directors of the Company prior to the Inducement Plan’s adoption date. In May 2021, the Board approved an amendment to the Inducement Plan to reserve an additional 1,000,000 shares of the Company’s common stock for issuance pursuant to the Inducement Plan. As of December 31, 2022, 1,053,767 shares of common stock were available for issuance under the Inducement Plan.

A summary of stock option activity under the 2015 Plan, 2017 Plan and Inducement Plan for the year ended December 31, 2022 is presented below:

	*Stock Options Outstanding*
	*Number of shares*			*Weighted average exercise price*		*Weighted average remaining life (in years)*
Balances — December 31, 2021		5,996,813		$	15.77		7.33
Options granted		1,440,100			2.97
Options exercised		—			—
Options canceled		(1,472,385	)		14.88
Options expired		(713,832	)		14.62
Balances — December 31, 2022		5,250,696		$	12.67		6.24
Exercisable — December 31, 2022		3,479,531		$	15.17		5.06

Time-based Options

The Company awards time-based options which vest and become exercisable, subject to the individual’s continued employment or service through the applicable vesting date. Time-based options can have various vesting schedules, most commonly new hire grants which generally vest 25% per year starting upon the first anniversary of the grant.

A summary of the time-based stock option activity under the 2015 Plan, 2017 Plan and Inducement Plan for the year ended December 31, 2022 is presented below:

	*Stock Options Outstanding*
	*Number of shares*			*Weighted average exercise price*		*Weighted average remaining life (in years)*
Balances — December 31, 2021		4,796,716		$	16.44		7.05
Options granted		1,240,100			2.59
Options exercised		—			—
Options canceled		(674,465	)		16.73
Options expired		(631,957	)		15.05
Balances — December 31, 2022		4,730,394		$	12.95		6.16
Exercisable — December 31, 2022		3,230,670		$	15.39		5.07

The intrinsic value of time-based options exercised during the years ended December 31, 2022, 2021 and 2020 was zero, $0.8 million, and $1.6 million, respectively.

The fair value of the time-based options granted to employees and directors during the years ended December 31, 2022, 2021 and 2020 was $2.3 million, $15.1 million, and $6.7 million, respectively.

Performance Options

Certain stock options awarded to the Company’s executives and other employees contain performance conditions related to certain financial measures and achievements of strategic/operational milestones. The options will vest and become exercisable once the specific performance condition is fulfilled.

A summary of the performance option activity under the 2017 Plan and Inducement Plan for the year ended December 31, 2022 is presented below:

	*Stock Options Outstanding*
	*Number of shares*			*Weighted average exercise price*		*Weighted average remaining life (in years)*
Balances — December 31, 2021		1,200,097		$	13.11		8.44
Options granted		200,000			5.32
Options exercised		—			—
Options canceled		(797,920	)		13.32
Options expired		(81,875	)		11.28
Balances — December 31, 2022		520,302		$	10.08		7.02
Exercisable — December 31, 2022		248,861		$	12.25		4.92

The fair value of the performance options granted to employees during the years ended December 31, 2022, 2021 and 2020 was $0.8 million, $2.5 million, and $5.5 million, respectively.

The fair value of employee stock options was estimated using the Black-Scholes option-pricing model utilizing the following assumptions:

	*Year Ended December 31,*
	*2022*	*2021*	*2020*
Expected term in years	5.3 - 6.8	5.3 - 6.1	5.3 - 6.1
Expected volatility	83 - 88%	78%	70%
Risk-free interest rate	1.9 - 3.2%	0.9 - 1.4%	0.3 - 0.5%
Dividend yield	—	—	—

2017 Employee Stock Purchase Plan

The Board previously adopted and the stockholders approved the Company’s 2017 Employee Stock Purchase Plan (the “2017 ESPP”).

The 2017 ESPP is a broad-based plan that provides employees of the Company and its designated affiliates with the opportunity to become stockholders through periodic payroll deductions that are applied towards the purchase of Company common shares at a discount from the then-current market price. Subject to adjustment in the case of certain capitalization events, a total of 250,000 common shares of the Company were available for purchase at adoption of the 2017 ESPP. Pursuant to the 2017 ESPP, the annual share increase pursuant to the evergreen provision is determined based on the least of (i) 450,000 shares, (ii) 1.5% of the Company’s common stock outstanding at December 31 of the immediately preceding year, or (iii) such number of shares as determined by the Board. In 2020 the Board determined not to increase the number of shares of common stock available pursuant to the evergreen provision. Effective January 1, 2021, pursuant to the evergreen provision of the 2017 ESPP, the number of shares of common stock available under the 2017 ESPP was increased by 383,250 shares. During the years ended December 31, 2022 and 2021, the Company issued 188,097 and 91,378 shares of common stock under the 2017 ESPP, respectively. As of December 31, 2022, 460,999 shares of common stock remained available for issuance under the 2017 ESPP.

The fair value of ESPP was estimated using the Black-Scholes option-pricing model utilizing the following assumptions:

	*Year Ended December 31,*
	*2022*	*2021*	*2020*
Expected term in years	0.5 - 1.0	0.5 - 1.0	0.5 - 1.0
Expected volatility	83%	78%	70	%
Risk-free interest rate	0.6% - 3.5%	0.06% - 0.1%	0.1% - 1.0%
Dividend yield	—	—	—

Restricted Stock Units

The fair value of RSU awards is determined based on the number of units granted and the closing price of the Company’s common stock as of the grant date. The estimated fair value of RSUs is recognized on a straight-line basis over the requisite service period.

During the year ended December 31, 2017, the Company granted 160,974 RSUs to the Chief Executive Officer, all of which vested in June 2018. These shares were partially released in 2019, resulting in a net issuance of shares. Additional paid in capital was reduced for tax payments related to shares withheld in connection with the release. The remaining shares under this grant were released in 2021, and at December 31, 2022 no shares were outstanding under this grant. There was no stock-based compensation expense related to these RSUs recorded in the years ended December 31, 2022, 2021 and 2020. As of December 31, 2022, there was no unrecognized compensation expense related to these RSUs.

During the year ended December 31, 2017, the Company granted 68,800 RSUs to certain employees, of which 50% vested on June 1, 2019 while the remaining 50% vested on June 1, 2021. The stock-based compensation expense recorded in the years ended December 31, 2022, 2021 and 2020 related to these RSUs was approximately zero million, $0.1 million, and $0.3 million, respectively. As of December 31, 2022, there was no unrecognized compensation expense related to these RSUs.

Stock-based Compensation

Total stock-based compensation expense recorded in the consolidated statements of operations and comprehensive loss was as follows (in thousands):

	*Year Ended December 31,*
	*2022*		*2021*		*2020*
Cost of revenues	$	217	$	129	$	—
Research and development		1,563		5,211		4,013
Sales and marketing		733		2,749		1,187
General and administrative		2,678		6,512		4,875
Total stock-based compensation expense	$	5,191	$	14,601	$	10,075

As of December 31, 2022, not all of the performance conditions of the performance options are probable to be achieved. Compensation expense has only been recognized for those conditions that are assumed to be probable.

In February 2021, the Compensation Committee approved of a modification to certain vesting conditions of outstanding Performance Options. The Company had not recognized any compensation expense in relation to these Performance Options as the performance condition was previously deemed to be improbable. However, upon modification those specific performance conditions were deemed probable and fully vested. As such, during the year ended December 31, 2021 the full expense in relation to the amended performance conditions was recognized resulting in $4.1 million of additional stock-compensation expense.

In October 2021, the Board amended the outstanding option awards of Kenneth A. Clark upon his resignation from the Board. The requirement that Mr. Clark exercise his vested options within ninety days of his resignation was waived. Mr. Clark will have the ability to exercise his outstanding vested option awards at any time during their ten-year term from the date of each grant, subject to earlier termination as may occur under the 2017 Plan. This amendment resulted in $1.4 million of additional stock-compensation expense during the year ended December 31, 2021.

Total stock-based compensation expense by award type was as follows (in thousands):

	*Year Ended December 31,*
	*2022*		*2021*		*2020*
Time-based options	$	4,467	$	9,235	$	8,739
Performance options		233		4,840		133
RSU		—		—		86
ESPP		491		526		1,117
Total stock-based compensation expense	$	5,191	$	14,601	$	10,075

At December 31, 2022, there was $5.6 million of unrecognized compensation cost related to unvested stock-based compensation arrangements, which is expected to be recognized over a weighted average period of 2.25 years.

Note 6 - Stockholders' Equity and Stock-based Compensation - Summary of Time-based Option Activity (Details) - Time-based Options [Member] - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Options balances, number of shares (in shares)	4,796,716
Options balances, weighted average exercise price (in dollars per share)	$ 16.44
Options balances, weighted average remaining life (Year)	6 years 1 month 28 days	7 years 18 days
Options granted, number of shares (in shares)	1,240,100
Options granted, weighted average exercise price (in dollars per share)	$ 2.59
Options exercised, number of shares (in shares)	0
Options exercised, weighted average exercise price (in dollars per share)	$ 0
Options canceled, number of shares (in shares)	(674,465)
Options canceled, weighted average exercise price (in dollars per share)	$ 16.73
Options expired, number of shares (in shares)	(631,957)
Options expired, weighted average exercise price (in dollars per share)	$ 15.05
Options balances, number of shares (in shares)	4,730,394	4,796,716
Options balances, weighted average exercise price (in dollars per share)	$ 12.95	$ 16.44
Options exercisable, number of shares (in shares)	3,230,670
Options exercisable, weighted average exercise price (in dollars per share)	$ 15.39
Options exercisable, weighted average remaining life (Year)	5 years 25 days

Note 8 - Controlled Launch

12 Months Ended

Dec. 31, 2022

Controlled Launch [Text Block]

8. Controlled Launch

In February 2021, the Company received 510(k) clearance from the FDA for its proprietary CellFX System for dermatologic procedures requiring ablation and resurfacing of the skin. In January 2021, the Company received CE marking approval for the CellFX System, which allows for marketing of the system in the EU for treatment of general dermatologic conditions, including SH, SK, and cutaneous non-genital warts. Additionally, in June 2021 the Company received Health Canada approval for the CellFX System, which allows for marketing of the system in Canada for use in dermatological procedures requiring ablation and resurfacing of the skin for the reduction, removal, and/or clearance of cellular-based benign lesions. In February 2021, the Company commenced a controlled launch of the CellFX System in the United States and European Union via its CellFX Expectations Excelled Program (the “Controlled Launch”). Subsequent to receiving Health Canada approval in June 2021, the Company also commenced its Controlled Launch in Canada.

As part of the Controlled Launch, the Company selected 70 physicians and their practices to be the first physician consultants to launch the CellFX System and the associated CellFX commercial procedures into their respective markets and geographies. In the Controlled Launch program, the Company provided and set up a CellFX System at each physician site and provided the physician with the necessary related products and components, free of charge, to complete the requirements of the Controlled Launch program. Each CellFX System and any unused component products remained the property of the Company throughout the Controlled Launch program. Under the Controlled Launch program, each physician was to identify and recruit up to 40 or 50 patients, depending on the contract, for participation in the Controlled Launch, performing a CellFX procedure on each of the appropriately selected patients. The physician and their patients complete evaluation surveys about their experiences with the CellFX System and provided other information helpful to the Company. Upon completion of the procedures and the survey feedback, the physician earned credits to be used towards the future purchase of the CellFX System or, in some jurisdictions, fair payment for their time and effort completing the paperwork required under the Controlled Launch program. Credits earned and, if applicable, any other payments earned were limited to a maximum amount dependent on the number of surveys received by the Company. Upon completion of the Controlled Launch program requirements, each physician could choose to enter into a purchase agreement with the Company, under which the physician could use the credits earned (or other payments earned, as applicable) towards the purchase of the already-delivered CellFX System, or the physician could return the CellFX System to the Company.

As patient procedures and surveys were completed under the Controlled Launch program, the Company accrued the value of the credits earned, which were recorded in accrued expenses, with a corresponding charge to sales and marketing expense. During the years ended December 31, 2022 and 2021 the Company recorded $0.1 million and $1.8 million, respectively, of net sales and marketing expense in relation to the Controlled Launch.

During the year ended December 31, 2022, certain consultants completed the Controlled Launch and entered into purchase agreements with the Company, whereby they used their credits or other earned payments towards the purchase of a CellFX System. Accordingly, approximately $0.4 million of the accrued liability related to the Controlled Launch was relieved and recognized as revenue on a non-cash basis as a result of the purchase. See Note 9 for additional detail of revenue transactions.

In September 2022, the Company concluded the Controlled Launch program and notified all remaining program participants. In accordance with the Controlled Launch program, physicians having completed the program requirements could elect to purchase their already delivered CellFX System, applying credits earned, or return the CellFX System to the Company. The Company concluded these efforts in the fourth quarter of 2022 and has discontinued sales of the CellFX System, although the Company continues to offer its disposable treatment tips to dermatologists who have chosen to retain their existing CellFX consoles.

Note 3 - Investments and Fair Value of Financial Instruments - Financial Assets Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Total assets measured at fair value	$ 57,973	$ 23,675
Total assets measured at fair value	(57,973)	(23,675)
Fair Value, Inputs, Level 1 [Member]
Total assets measured at fair value	57,973	23,675
Total assets measured at fair value	(57,973)	(23,675)
Fair Value, Inputs, Level 2 [Member]
Cash and Cash equivalents		0
Total assets measured at fair value	(0)
Total assets measured at fair value	0
Fair Value, Inputs, Level 3 [Member]
Total assets measured at fair value	0	0
Total assets measured at fair value	0	0
Money Market Funds [Member]
Cash and Cash equivalents	57,973	23,675
Money Market Funds [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash and Cash equivalents	57,973	23,675
Money Market Funds [Member] \| Fair Value, Inputs, Level 2 [Member]
Cash and Cash equivalents	0	0
Money Market Funds [Member] \| Fair Value, Inputs, Level 3 [Member]
Cash and Cash equivalents	$ 0	$ 0

Note 1 - Description of Business

12 Months Ended

Dec. 31, 2022

Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]

1. Description of the Business

Pulse Biosciences, Inc. is a novel bioelectric medicine company committed to health innovation using its patented Nano-Pulse Stimulation (“NPS”) technology, a revolutionary energy modality that delivers nanosecond-duration pulses of electrical energy, each less than a millionth of a second long, to non-thermally clear targeted cells while sparing adjacent noncellular tissue. NPS technology, also referred to as a Nanosecond Pulsed-Field Ablation (“nsPFA”) technology when used to ablate cellular tissue, can be used to treat a variety of medical conditions for which an optimal solution remains unfulfilled. The Company developed its proprietary CellFX System, a novel nsPFA delivery platform, and commercialized the initial application of its nsPFA technology to treat benign lesions of the skin. In parallel, the Company has designed a variety of applicators to explore the potential use of the CellFX platform to treat disorders in other medical specialties, such as cardiology, gastroenterology, gynecology, and ear nose and throat. These applicators include devices for open surgical procedures, endoscopic or minimally invasive procedures, and endoluminal catheters, and each has been used in preclinical studies. Based on our preclinical experience and the potential to significantly improve outcomes for patients in a large and growing market, the Company decided in 2022 to focus its efforts on the use of nsPFA and the CellFX platform in the treatment of atrial fibrillation (“AF”)

The Company was incorporated in Nevada on May 19, 2014. On June 18, 2018, the Company reincorporated from the State of Nevada to the State of Delaware. The Company is located in Hayward, California.

The Company’s activities are subject to significant risks and uncertainties, including the need for additional capital. The Company does not currently have any material cash flows from operations. It has minimal revenue and will need to raise additional capital to finance its operations. However, there can be no assurances that the Company will be able to obtain additional financing on acceptable terms and in the amounts necessary to fully fund its operating requirements.

Note 13 - Commitments and Contingencies

12 Months Ended

Dec. 31, 2022

Commitments and Contingencies Disclosure [Text Block]

13. Commitments and Contingencies

2021 Loan Agreement

On March 11, 2021, the Company and Robert W. Duggan, the Executive Chairman, entered into a Loan Agreement in connection with Mr. Duggan lending the principal sum of $41.0 million to the Company. The Loan Agreement bore interest at a rate per annum equal to 5.0%, payable quarterly commencing on July 1, 2021. During the year ended December 31, 2021, the Company recorded $0.6 million of interest expense in relation to this Loan Agreement. In June 2021, the Loan Agreement was terminated and $41.0 million principal, together with approximately $0.6 million of accrued and unpaid interest, was fully settled via issuance of the Company’s common stock at a price per share of $16.40. Refer to Note 6 for additional details of the private placement sale.

2022 Loan Agreement

On September 20, 2022, the Company and Robert W. Duggan, the Executive Chairman, entered into a Loan Agreement (“2022 Loan Agreement”) in connection with Mr. Duggan lending the principal sum of $65.0 million to the Company. The Loan Agreement bears interest at a rate per annum equal to 5.0%, payable quarterly commencing on January 1, 2023, with the principal sum payable on March 20, 2024. On March 17, 2023, the Company and Mr. Duggan agreed to amend certain terms of the Loan Agreement. There were no changes to the interest rate, but the principal sum is now due and payable on September 30, 2024. During the year ended December 31, 2022, the Company recorded $0.9 million of interest expense in relation to the 2022 Loan Agreement.

Insurance Loan Agreement

On May 13, 2021, the Company secured its annual director and officer liability insurance policy. The total premiums for the policy were approximately $2.6 million, of which the Company made a down payment of $0.7 million and financed the balance of $1.9 million via an Insurance Loan Agreement. The Insurance Loan Agreement had an annual interest rate of 3.69% and required monthly payments through February 2022, upon which the Insurance Loan Agreement was paid in full. During the year ended December 31, 2022, the Company recorded $1.0 thousand of interest expense in relation to the Insurance Loan Agreement.

Operating Leases

In January 2017, the Company entered into a five-year lease (the “Existing Lease”) for approximately 15,700 square feet for its corporate headquarters located in Hayward, California. The lease commenced during July 2017.

In May 2019, the Company entered into Lease Amendment 1 (the “Lease Amendment”) in relation to the Existing Lease and added the lease of new premises of approximately 13,300 square feet and 21,300 square feet, (“Expansion Premises 1” and “Expansion Premises 2,” respectively). Additionally, the term of the Existing Lease was extended to October 2029 to be coterminous with Expansion Premises 1 and Expansion Premises 2.

The Company evaluated the lease amendment under the provisions of ASC 842. It concluded that the Lease Amendment would be accounted for as a single contract with the Existing Lease because the additional lease payments due to the Lease Amendment was not commensurate with the right-of-use asset granted to the Company. Though the Lease Amendment was accounted for as a single contract, the Existing Premises, Expansion Premises 1 (occupied in November 2019) and Expansion Premises 2 (occupied in May 2020) are accounted for as separate lease components. Accordingly, the Company measured and allocated consideration to each lease component as of the modification date.

Upon commencement of each lease component, the Company reassessed and calculated the lease liability and right-of-use asset for the respective component. As a result, at the modification date, the Company remeasured its existing lease liability and recorded an additional right-of-use asset and lease liability of $2.0 million. The Company also recorded an additional right-of-use asset and lease liability of $3.0 million and $4.8 million at the commencement of Expansion Premises 1 in November 2019 and Expansion Premises 2 in May 2020, respectively. At December 31, 2022, total right-of-use assets and lease lability was approximately $8.1 million and $10.0 million, respectively.

During the years ended December 31, 2022, 2021 and 2020, rent expense, including common area maintenance charges, was $2.1 million, $1.9 million and $1.7 million, respectively.

Supplemental balance sheet information related to leases (in thousands):

	Year Ended December 31,
Assets:	2022		2021
Right-of-use assets	$	8,062	$	8,785

	Year Ended December 31,
Liabilities:	2022		2021
Current operating lease liabilities	$	896	$	774
Non-current operating lease liabilities		9,144		10,040
Total lease liabilities	$	10,040	$	10,814

Total cash paid for operating lease liabilities (in thousands):

	*Year Ended December 31,*
	*2022*		*2021*		*2020*
Cash paid for operating lease liabilities	$	1,806	$	1,643	$	1,045

Maturities of operating lease liabilities were as follows (in thousands):

Year ending December 31:
2023	$	1,845
2024		1,910
2025		1,977
2026		2,046
2027		2,117
Thereafter		4,074
Total lease payments		13,969
Less imputed interest		(3,929	)
Total lease liabilities	$	10,040

Weighted-average remaining lease term and discount rate, as of December 31, 2022, were as follows:

Weighted-average remaining lease term			6.83
Weighted-average discount rate			10	%

Legal Proceedings

From time to time, we may be involved in a variety of claims, lawsuits, investigations, and proceedings relating to securities laws, product liability, patent infringement, contract disputes, and other matters relating to various claims that arise in the normal course of our business, including the matter described below. The outcome of any legal proceedings is unpredictable but, regardless of outcome, they can have an adverse impact on us because of defense and settlement costs, diversion of management resources, negative publicity, reputational harm, and other factors. We maintain insurance that may provide coverage for such matters, including customary employment practices liability insurance.

In November 2022, the employment of our former Chief Financial Officer, Sandra Gardiner, terminated. Ms. Gardiner’s departure was not the result of any disagreement with the Company on any matter relating to its operations, accounting policies or practices, although the Company determined that she was not eligible to receive any severance benefits under the terms and conditions of her then existing employment agreement. In March 2023, Ms. Gardiner filed an arbitration demand with JAMS seeking severance benefits and other remedies, alleging breach of contract and unlawful termination in violation of public policy, among other things. We believe that Ms. Gardiner’s claims are without merit and we intend to vigorously defend ourselves against them. Because of the difficulty in predicting the outcome of any legal proceeding, particularly one that is in its early stages, the Company cannot predict what the final outcome of Ms. Gardiner’s arbitration proceeding will likely be. However, at this time, we believe that the final resolution of this matter will not adversely affect our consolidated position, results of operation, or cash flows.

Consolidated Balance Sheets (Parentheticals) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares issued (in shares)	37,235,000	29,716,000
Common stock, shares outstanding (in shares)	37,235,000	29,716,000

Note 6 - Stockholders' Equity and Stock-based Compensation - ESPP Assumptions (Details) - The 2017 Employee Stock Purchase Plan [Member]	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Expected volatility	83.00%	78.00%	70.00%
Dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Expected term in years (Year)	6 months	6 months	6 months
Risk-free interest rate	0.60%	0.06%	0.10%
Maximum [Member]
Expected term in years (Year)	1 year	1 year	1 year
Risk-free interest rate	3.50%	0.10%	1.00%

Note 3 - Investments and Fair Value of Financial Instruments (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Impairment of Marketable Securities	$ 0	$ 0
Fair Value, Level 1, 2 and 3 Transfers, Amount	0	0
Assets, Fair Value Disclosure, Total	57,973	23,675
Fair Value, Nonrecurring [Member]
Liabilities, Fair Value Disclosure, Total	0	0	$ 0
Assets, Fair Value Disclosure, Total	$ 0	$ 0	$ 0

Note 4 - Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2022

Schedule of Inventory, Current [Table Text Block]

	*Year Ended December 31,*
	*2022*		*2021*
Raw materials	$	—	$	2,010
Work in process		—		1,371
Finished goods		—		2,443
Total inventory	$	—	$	5,824

Property, Plant and Equipment [Table Text Block]

	*December 31,*
	*2022*			*2021*
Leasehold improvements	$	2,519		$	2,519
Laboratory equipment		1,118			1,019
Furniture, fixtures and equipment		966			932
Software		289			202
Construction in progress		22			186
		4,914			4,858
Less: Accumulated depreciation and amortization		(2,953	)		(2,396	)
	$	1,961		$	2,462

Schedule of Finite-Lived Intangible Assets [Table Text Block]

	*December 31,*
	*2022*			*2021*
Acquired patents and licenses	$	7,985		$	7,985
Less: Accumulated amortization		(5,434	)		(4,769	)
	$	2,551		$	3,216

Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]

Years ending December 31:
2023	$	665
2024		665
2025		665
2026		556
	$	2,551

Schedule of Accrued Liabilities [Table Text Block]

	*December 31,*
	*2022*		*2021*
Compensation expense	$	1,377	$	2,932
Controlled launch (Note 8)		—		534
Director and officer liability insurance (Note 12)		571		—
Clinical trial fees and costs		64		245
Professional fees		318		85
Warranty		50		80
Other		215		513
	$	2,595	$	4,389

Note 13 - Commitments and Contingencies - Information Related to Right-of-use Assets and Lease Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Right-of-use assets	$ 8,062	$ 8,785
Current operating lease liabilities	896	774
Non-current operating lease liabilities	9,144	10,040
Total lease liabilities	10,040	10,814
Cash paid for operating lease liabilities	1,806	$ 1,643	$ 1,045
2023	1,845
2024	1,910
2025	1,977
2026	2,046
2027	2,117
Thereafter	4,074
Total lease payments	13,969
Less imputed interest	$ (3,929)
Weighted-average remaining lease term (Year)	6 years 9 months 29 days
Weighted-average discount rate	10.00%

Note 11 - Income Taxes - Components of Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Current
Federal	$ 0	$ 0	$ 0
State	3	3	3
Foreign	0	0	0
Total current	3	3	3
Deferred
Federal	0	0	0
State	0	0	0
Foreign	0	0	0
Total deferred	0	0	0
Total provision for income taxes	$ 3	$ 3	$ 3

Note 11 - Income Taxes - Income (Loss) Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Domestic	$ (58,505)	$ (63,660)	$ (49,851)
Foreign	0	0	0
Loss from operations, before income taxes	$ (58,505)	$ (63,660)	$ (49,851)

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8906-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (f)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 25
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=126941158&loc=d3e41242-110953

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(10))
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(8))
-URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(b)(2))
-URI https://asc.fasb.org/extlink&oid=120399901&loc=d3e537907-122884

Reference 9: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8924-108599

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(15))
-URI https://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Consolidated Statements of Stockholders' Equity (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Rights Offering [Member]
Offering price per unit (in dollars per share)			$ 7.01
Issuance cost	$ 136		$ 565
Private Placement [Member]
Issuance cost		$ 106
ATM Offering [Member]
Issuance cost		$ 568

Note 10 - Segment Reporting (Details Textual)	12 Months Ended
Note 10 - Segment Reporting (Details Textual)	Dec. 31, 2022
Number of Reportable Segments	1

Note 6 - Stockholders' Equity and Stock-based Compensation - Summary of Warrants Activity (Details)	12 Months Ended
	Dec. 31, 2022 $ / shares shares
Warrants outstanding, number of shares (in shares) \| shares	0
Warrants outstanding, weighted average exercise price (in dollars per share) \| $ / shares	$ 0
Warrants issued, number of shares (in shares) \| shares	7,317,072
Warrants issued, weighted average exercise price (in dollars per share) \| $ / shares	$ 2.05
Warrants exercised, number of shares (in shares) \| shares	(13,240)
Warrants exercised (in dollars per share) \| $ / shares	$ 2.05
Warrants Expired/Redeemed, number of shares (in shares) \| shares	0
Warrants Expired/Redeemed, weighted average exercise price (in dollars per share) \| $ / shares	$ 0
Warrants outstanding, number of shares (in shares) \| shares	7,303,832
Warrants outstanding, weighted average exercise price (in dollars per share) \| $ / shares	$ 2.05
Warrants outstanding, weighted average remaining contractual life (Year)	4 years 5 months 4 days

Note 12 - Related Party Transactions

12 Months Ended

Dec. 31, 2022

12. Related Party Transactions

On March 11, 2021, the Company and Robert W. Duggan, majority stockholder and Executive Chairman, entered into the 2021 Loan Agreement in connection with Mr. Duggan lending the principal sum of $41.0 million to the Company (Note 13).

On June 30, 2021, the Company and Mr. Duggan entered into a Securities Purchase Agreement (Note 6), pursuant to which the Company issued and sold to Mr. Duggan 3,048,780 shares of the Company’s common stock, par value $0.001 per share, in a Private Placement, at a price per share of $16.40, for an aggregate investment in the amount of $50.0 million. The shares were paid for through (i) the conversion of the $41 million aggregate principal amount under the Loan Agreement, together with all accrued and unpaid interest outstanding, owed to Mr. Duggan under the Loan Agreement by and between the Company and Mr. Duggan (Note 13), and (ii) additional cash in the amount of approximately $8.4 million. Upon the closing of this Private Placement and satisfaction of the outstanding debt, the Loan Agreement terminated, without any early termination fees or penalties being owed by the Company, and no additional amounts were owed to Mr. Duggan under the Loan Agreement.

In May 2022, the Company determined not to renew its annual director and officer liability insurance policy due to disproportionately high premiums quoted by insurance companies. Instead, on May 31, 2022, the Company and Robert W. Duggan, the Executive Chairman, entered into a letter agreement (the “Letter Agreement”) pursuant to which Mr. Duggan has agreed with the Company to personally provide indemnity coverage for a one-year period, and he has agreed to deposit cash and/or marketable securities into a third-party escrow, as security for these obligations, if requested by the Company. The Company will pay a fee of $1.0 million to Mr. Duggan that shall be due on May 31, 2023, the last day of the one-year period, in consideration of the obligations set forth in the Letter Agreement. As of December 31, 2022, the amount owed to Mr. Duggan under the Letter Agreement was $0.6 million, recorded on the balance sheet under accrued expenses.

On September 20, 2022, the Company and Robert W. Duggan, majority stockholder and Executive Chairman, entered into the 2022 Loan Agreement in connection with Mr. Duggan lending the principal sum of $65.0 million to the Company (Note 13).

Note 4 - Balance Sheet Components (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Depreciation, Total	$ 690	$ 480	$ 430
Finite-Lived Intangible Asset, Useful Life (Year)	12 years

Note 9 - Revenue (Details Textual) - USD ($) $ in Thousands	12 Months Ended
Note 9 - Revenue (Details Textual) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenue from Contract with Customer, Excluding Assessed Tax	$ 700	$ 1,418	$ 0
Redemption of Non Cash Credits [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 400	$ 1,100

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8906-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9031-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9038-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130543-203045

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9054-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130545-203045

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI https://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (58,505)	$ (63,660)	$ (49,851)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	690	480	430
Amortization of intangible assets	665	666	665
Stock-based compensation	5,191	14,601	10,075
Write-off of excessive and obsolete inventory	8,477	0	0
Net premium amortization and discount on available-for-sale securities	0	13	5
Loss on disposal of fixed assets	185	0	119
Gain on U.S. Treasury securities	0	0	(8)
Changes in operating assets and liabilities:
Accounts receivable	61	(61)	0
Inventory	(2,653)	(5,824)	0
Prepaid expenses and other current assets	1,164	(1,374)	194
Other receivables	(41)	54	0
Right-of-use assets	723	653	509
Other long-term assets	0	0	129
Accounts payable	(1,304)	1,160	(266)
Accrued expenses	(1,794)	(937)	2,830
Deferred revenue	(16)	16	0
Lease liabilities	(774)	(542)	(196)
Accrued interest on related party note payable	917	0	0
Accrued interest on note payable	1	658	0
Net cash used in operating activities	(47,013)	(54,097)	(35,365)
Cash flows from investing activities:
Purchases of property and equipment	(401)	(437)	(441)
Purchases of investments	0	0	(29,025)
Maturities of investments	0	8,000	35,000
Sales of investments	0	0	4,510
Net cash provided by (used in) investing activities	(401)	7,563	10,044
Cash flows from financing activities:
Proceeds from issuance of common stock under employee stock purchase plan	486	810	490
Proceeds from exercises of warrants	26	4,217	244
Proceeds from exercises of stock options	0	786	717
Proceeds from issuance of common stock	14,864	56,697	29,434
Proceeds from issuance of related party note	65,000	0	0
Proceeds from insurance loan agreement	0	1,939	0
Payments made on insurance loan agreement	(437)	(1,532)	0
Tax payments related to shares withheld for vested restricted stock units	0	(232)	0
Net cash provided by financing activities	79,939	62,685	30,885
Net increase in cash and cash equivalents	32,525	16,151	5,564
Cash and cash equivalents at beginning of period	28,614	12,463	6,899
Cash and cash equivalents at end of period	61,139	28,614	12,463
Supplemental disclosure of noncash investing and financing activities:
Other receivable from exercise of warrants and stock options	0	0	1,053
Change in unrealized gains on available-for-sale securities	0	1	(5)
Equipment purchases included in accounts payable and accrued expenses	(27)	(27)	(20)
Equipment purchases included in accounts payable and accrued expenses	27	27	20
Accrued interest settled via issuance of common stock from private placement equity offering	$ 0	$ 629	$ 0

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenues:
Total revenues	$ 700	$ 1,418	$ 0
Cost and expenses:
Cost of revenues	11,944	1,968	0
Research and development	20,839	28,640	26,444
Sales and marketing	12,019	14,751	7,256
General and administrative	13,955	19,073	16,265
Total cost and expenses	58,757	64,432	49,965
Loss from operations	(58,057)	(63,014)	(49,965)
Other income (expense):
Interest income (expense), net	(448)	(646)	114
Total other income (expense)	(448)	(646)	114
Loss from operations, before income taxes	(58,505)	(63,660)	(49,851)
Income tax benefit	0	0	0
Net loss	(58,505)	(63,660)	(49,851)
Other comprehensive gain (loss):
Unrealized gain (loss) on available-for-sale securities	0	1	(5)
Comprehensive loss	$ (58,505)	$ (63,659)	$ (49,856)
Net loss per share:
Basic and diluted net loss per share (in dollars per share)	$ (1.72)	$ (2.28)	$ (2.14)
Weighted average shares used to compute net loss per common share — basic and diluted (in shares)	33,935	27,964	23,248
Product [Member]
Revenues:
Total revenues	$ 700	$ 1,418	$ 0

Note 2 - Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2022

Significant Accounting Policies [Text Block]

2. Summary of Significant Accounting Policies

Basis of Presentation

Certain prior period balances have been reclassified to conform to the current period presentation in the consolidated financial statements and the accompanying notes. Sales and marketing expenses are reclassified out of general and administrative expenses, both of which are presented as separate line items. Amortization of intangible assets are reclassified to general and administrative expenses.

Principles of Consolidation

The accompanying consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and pursuant to the rules and regulations of the United States Securities Exchange Commission (the “SEC”). The consolidated financial statements include the financial statements of the Company and its wholly-owned subsidiaries and intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires the Company to make estimates that affect the amounts reported in the financial statements and accompanying notes to the financial statements. Estimates include, but are not limited to, the valuation and recognition of share-based compensation, inventory valuation, warranty obligations, income taxes, and the useful lives assigned to long-lived assets. The Company evaluates its estimates and assumptions based on historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ materially from these estimates.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents and investments. The Company places its cash equivalents and investments with high credit quality financial institutions and, by policy, limits the amounts invested with any one financial institution or issuer. Deposits held with banks may exceed the amount of insurance provided on such deposits. The Company has not experienced any losses since inception.

Fair Value of Financial Instruments

The Company believes the carrying amounts of its financial instruments, including cash equivalents, prepaid expenses and other current assets, accounts payable and accrued expenses, approximate fair value due to the short-term nature of such instruments.

Cash and Cash Equivalents

The Company invests its cash primarily in money market funds. The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents.

Property and Equipment

Property and Equipment is recorded at cost and depreciated using the straight-line method over their estimated useful lives, ranging from three to five years. Leasehold improvements are amortized using the straight-line method over the shorter of the lease term or estimated useful life. Upon the sale or retirement of property and equipment, the costs and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is reflected in operating expenses. Maintenance and repairs are charged to operations as incurred.

Valuation of Inventory

Inventory is stated at lower of cost or net realizable value. The Company establishes the inventory basis by determining the cost based on standard costs approximating the purchase costs on a first-in, first-out basis. Net realizable value is the estimated selling price in the ordinary course of the Company’s business, less reasonably predictable costs of completion, disposal, and transportation. The cost basis of the Company’s inventory will be reduced for any products that are considered excessive or obsolete based upon assumptions about future demand and market conditions. At December 31, 2022, the inventory balance has been fully written off due to excessive and obsolete inventory.

Intangible Assets

The Company’s intangible assets consist of acquired patents and licenses, which are amortized over their estimated useful lives of twelve years.

Long-Lived Assets

The Company reviews long-lived assets, consisting of property and equipment and intangible assets, for impairment during each fiscal year or when events or changes in circumstances indicate the carrying value of these assets may exceed their current fair values. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the estimated undiscounted future cash flows expected to be generated by the asset. No impairment losses were incurred during the periods presented.

Goodwill

The Company records goodwill when the consideration paid in a business acquisition exceeds the fair value of the net tangible assets and the identified intangible assets acquired. The Company reviews goodwill for impairment at the reporting unit level at least annually or whenever changes in circumstances indicate that the carrying value of the goodwill may not be recoverable. To date, there has been no impairment of goodwill.

Revenue from Contracts with Customers

The Company recognizes revenue at a point in time when it satisfies performance obligations by transferring control of promised goods to its customers. The amount of revenue recognized is equal to the consideration which the Company is entitled to in exchange for the promised goods, excluding any amounts assessed by government authorities for taxes which might be collected from a customer. Sales contracts often involve the sale and delivery of multiple products, each of which typically represent a separate performance obligation in the contract. While the Company sells these products on a stand-alone basis at their respective SSP, initial customer contracts will likely involve the bundling of products which will be delivered concurrently to the customer. In such instances, the full consideration of the contract will be recognized upon shipment of the products. The Company generally requires receipt of full payment prior to shipment, however, from time to time, payment terms may be extended to customers upon which the Company will perform a necessary credit evaluation to ensure future collectability of the outstanding balance. Refer to Note 9 for further details.

Product Warranty

The Company provides a standard warranty on eligible products which provides the customer assurances that the products comply with the agreed-upon specifications. The standard warranty does not provide any services in addition to those assurances. The Company accrues a warranty reserve for products sold based upon the best estimate of the nature, frequency, and costs of future claims. These estimates are inherently uncertain given the short history of sales, and changes to the historical or projected warranty experience may cause material changes to the warranty reserve in the future. The warranty reserve is included within Accrued expenses on the consolidated balance sheets. Warranty expense is recorded as a component of Cost of Revenues in the consolidated statements of operations and comprehensive loss.

Warranty accrual activity consisted of the following (in thousands):

Year Ended December 31,

2022

2021

Beginning balance
$ 80 $ —

Add: Accruals for warranties issued during the period
42 80

Less: Adjustment for inventory at cost and excessive and obsolete inventory
(72 ) —

Ending balance
$ 50 $ 80

Stock-Based Compensation

The Company recognizes the cost of stock-based compensation in the financial statements based upon fair value. The fair value of stock options is determined as of the grant date using the Black-Scholes option pricing model. The fair value of Restricted Stock Units (“RSU”) awards is determined based on the number of units granted and the closing price of the Company’s common stock on the grant date. The fair value of each purchase under the employee stock purchase plan (“ESPP”) is estimated at the beginning of the offering period using the Black-Scholes option pricing model. The Company’s determination of the fair value of equity-settled awards is impacted by the price of the Company’s common stock as well as changes in assumptions regarding a number of complex and subjective variables. These variables include, but are not limited to, the expected term that awards will remain outstanding, expected common stock price volatility over the term of the awards, risk-free interest rates and expected dividends. The fair value of an award is recognized over the period during which service is required to be performed in exchange for the award, the requisite service period (usually the vesting period) on a straight-line basis. The Company accounts for all equity instruments awarded to non-employees at the fair value of the award issued on the day of the grant. The fair value of these equity instruments are expensed over the requisite service period. Certain stock options awarded to the Company’s executives and other key employees contain performance conditions related to certain financial measures and achievements of strategic/operational milestones (“performance options”). These performance options can contain both service and performance-based vesting conditions. The fair value of these performance options is recognized using the graded vesting method over the requisite service period beginning in the period in which the awards are deemed probable to vest, to the extent such awards are probable to vest.

Estimates of the fair value of equity-settled awards as of the grant date using valuation models, such as the Black-Scholes option pricing model, are affected by assumptions regarding a number of complex variables. Changes in the assumptions can materially affect the fair value of the award and the stock-based compensation expense recognized. These inputs are subjective and generally require significant analysis and judgment to develop. The Company determines the volatility factor based on its own historical volatility. The risk-free interest rate is based on the yield available on U.S. Treasury zero-coupon issues similar in duration to the expected term of the equity-settled award. For all stock options granted to date, the Company used the simplified method to calculate the expected term, which is the average of the contractual term and vesting period.

See Note 6 for a detailed discussion of the Company’s stock plans and stock-based compensation expense.

Research and Development Costs

Research and development costs consist primarily of compensation costs, fees paid to consultants and outside service providers and organizations (including university research institutes), costs associated with clinical trials, development prototypes and other expenses relating to the acquisition, design, development and testing of the Company’s product candidates, and certain facilities related costs. Research and development costs incurred by the Company are expensed as incurred, unless the achievement of milestones, the completion of contracted work, or other information indicates that a different expensing schedule is more appropriate.

Patent Costs

The Company is the owner of numerous domestic and foreign patents. Due to the significant uncertainty associated with the successful development of one or more commercially viable products based on the Company’s research efforts and any related patent applications, patent costs not related to acquired patents, including patent-related legal fees, filing fees and other costs, including internally generated costs, are expensed as incurred. During the years ended December 31, 2022, 2021 and 2020, patent costs totaled $0.5 million, $0.6 million and $0.5 million, respectively. Patent costs are included in general and administrative costs in the consolidated statements of operations and comprehensive loss.

Income Taxes

The Company accounts for income taxes under an asset and liability approach for financial accounting and reporting for income taxes. Accordingly, the Company recognizes deferred tax assets and liabilities for the expected impact of differences between the financial statements and the tax basis of assets and liabilities.

The Company records a valuation allowance to reduce its deferred tax assets to the amount that is more-likely-than-not to be realized. In the event the Company determines that it would be able to realize its deferred tax assets in the future in excess of its recorded amount, an adjustment to the deferred tax assets would be credited to operations in the period such determination was made. Likewise, should the Company determine that it would not be able to realize all or part of its deferred tax assets in the future, an adjustment to the deferred tax assets would be charged to operations in the period such determination was made.

The Company is subject to U.S. federal income taxes and state income taxes in various states. As the Company’s net operating losses have yet to be utilized, previous tax years remain open to examination by federal authorities and other jurisdictions in which the Company currently operates or has operated in the past. The Company is not currently under examination by any tax authority.

The Company accounts for uncertainties in income tax law under a comprehensive model for the financial statement recognition, measurement, presentation and disclosure of uncertain tax positions taken or expected to be taken in income tax returns as prescribed by U.S. GAAP. The tax effects of a position are recognized only if it is more-likely-than-not to be sustained by the taxing authority as of the reporting date. If the tax position is not considered more-likely-than-not to be sustained, then no benefits of the position are recognized. At December 31, 2022 and 2021, the Company had not recorded any liability for uncertain tax positions. The Company includes interest and penalties related to uncertain tax positions as a component of income tax expense.

Comprehensive Loss

Comprehensive loss consists of net loss and unrealized gains or losses on available-for-sale investments. The Company displays comprehensive loss and its components as part of the consolidated statements of operations and comprehensive loss.

Net Loss per Share

The Company calculates basic net loss per share by dividing net loss by the weighted average number of shares of common stock outstanding during the period. Diluted net loss per share is computed by giving effect to all potential dilutive common stock equivalents outstanding during the period. For purposes of this calculation, options to purchase common stock and common stock warrants are considered common stock equivalents. Potential common shares that have an anti-dilutive effect (i.e., those that increase income per share or decrease loss per share) are excluded from the calculation of diluted net loss per share.

The following outstanding stock options, warrants, and RSUs to purchase common stock were excluded from the computation of diluted net loss per share for the periods presented because including them would have had an anti-dilutive effect:

Year Ended December 31,

2022

2021

2020

Common stock warrants
7,303,832 — 612,310

Common stock options
5,250,696 5,996,813 5,039,194

Restricted stock units
— — 111,305

Total
12,554,528 5,996,813 5,762,809

Segment and Geographical Information

The Company operates in one segment and reports segment information in accordance with ASC 280, Segment Reporting. Management uses one measurement of profitability and does not segregate its business for internal reporting, however in making certain operating decisions and assessing performance, management will additionally review the disaggregated revenue results by product and geography. The Company’s Chief Executive Officer acts as the chief operating decision makers (“CODM”) of the Company. As of December 31, 2022 and 2021, 100% of long-lived assets were in the United States. Revenue is attributed to a geographic region based on the location of the end customer.

See Note 10 for details of revenue by product and geography.

Recent Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers, requiring an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. This updated standard became effective for the Company in the first quarter of fiscal year 2018. The Company began to recognize revenue in 2021 using this updated standard. See Note 9 for additional details of the revenue recognition approach.

In November 2018, the FASB issued ASU No. 2018-18 Collaborative Arrangements – Clarifying the Interaction between Topic 808 (Collaborative Arrangements) and Topic 606 (Revenue from Contracts with Customers), which clarifies the interaction between ASC 808, Collaborative Arrangements and ASC 606, Revenue from Contracts with Customers (“ASC 606”). The ASU clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC 606 when the counterparty is a customer. In addition, the ASU precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue if the counterparty is not a customer for that transaction. The Company adopted the standard on January 1, 2020, however, did not record revenue until August 2021 and does not currently have any collaborative arrangements in place. The adoption of the new standard had no impact on the Company’s consolidated financial statements.

In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which eliminates certain exceptions related to the general principles in ASC 740 and makes amendments to other areas with the intention of simplifying various aspects related to accounting for income taxes. The new standard is effective for fiscal years beginning after December 15, 2020, including interim periods therein; with early adoption permitted. The Company adopted the Topic 740 effective January 1, 2021. The adoption did not have a material impact on the Company’s financial statements.

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 61,139	$ 28,614
Accounts receivable	0	61
Inventory	0	5,824
Prepaid expenses and other current assets	1,008	2,131
Total current assets	62,147	36,630
Property and equipment, net	1,961	2,462
Intangible assets, net	2,551	3,216
Goodwill	2,791	2,791
Right-of-use assets	8,062	8,785
Other assets	365	365
Total assets	77,877	54,249
Current liabilities:
Accounts payable	1,573	2,904
Accrued expenses	2,595	4,389
Deferred revenue	0	16
Lease liability, current	896	774
Note payable, current	0	436
Related party note payable, current	917	0
Total current liabilities	5,981	8,519
Lease liability, less current portion	9,144	10,040
Related party note payable, less current	65,000	0
Total liabilities	80,125	18,559
Commitments and contingencies (Note 13)
Stockholders’ equity:
Preferred stock, $0.001 par value; authorized – 50,000 shares; no shares issued and outstanding	0	0
Common stock, $0.001 par value; authorized – 500,000 shares; issued and outstanding – 37,235 shares and 29,716 shares at December 31, 2022 and 2021, respectively	37	29
Additional paid-in capital	292,420	271,861
Accumulated other comprehensive income (loss)	0	0
Accumulated deficit	(294,705)	(236,200)
Total stockholders’ (deficit) equity	(2,248)	35,690
Total liabilities and stockholders’ equity	$ 77,877	$ 54,249

Note 16 - Supplementary Financial Information

12 Months Ended

Dec. 31, 2022

Quarterly Financial Information [Text Block]

16. Supplementary Financial Information

There are no retrospective changes to the statements of comprehensive income for any of the quarters within the two most recent fiscal years that individually or in the aggregate are material.

Note 13 - Commitments and Contingencies (Details Textual) $ in Thousands		1 Months Ended				3 Months Ended	12 Months Ended
	May 13, 2021 USD ($)	Jun. 30, 2021 USD ($)	May 31, 2020 USD ($)	Nov. 30, 2019 USD ($)	May 31, 2019 USD ($) a	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 20, 2022 USD ($)	May 11, 2021 USD ($)	Jul. 31, 2017 a
Director and Officer Insurance Premium Payable	$ 2,600
Payment to Acquire Life Insurance Policy, Investing Activities	700
Increase (Decrease) in Operating Lease Right of Use Asset							$ (723)	$ (653)	$ (509)
Operating Lease, Right-of-Use Asset							8,062	8,785
Operating Lease, Liability, Total							10,040	10,814
Operating Lease, Expense							2,100	$ 1,900	$ 1,700
Corporate Headquarters in Hayward, California [Member]
Lessee, Operating Lease, Term of Contract (Year)												5 years
Area of Real Estate Property (Acre) \| a												15,700
Increase (Decrease) in Operating Lease Right of Use Asset					$ 2,000
Operating Lease, Right-of-Use Asset							8,100
Operating Lease, Liability, Total							10,000
Corporate Headquarters in Hayward, California [Member] \| Expansion Premises 1 [Member]
Area of Real Estate Property (Acre) \| a					13,300
Increase (Decrease) in Operating Lease Right of Use Asset				$ 3,000
Corporate Headquarters in Hayward, California [Member] \| Expansion Premises 2 [Member]
Area of Real Estate Property (Acre) \| a					21,300
Increase (Decrease) in Operating Lease Right of Use Asset			$ 4,800
Board of Directors Chairman [Member] \| Conversion of Loan Agreement into Common Stock [Member]
Debt Conversion, Original Debt, Amount		$ 41,000
Interest Payable		$ 600
Debt Conversion, Converted Instrument, Rate		16.40%
Loan Agreement [Member] \| Board of Directors Chairman [Member]
Debt Instrument, Face Amount	41,000										$ 41,000
Debt Instrument, Interest Rate, Stated Percentage											5.00%
Interest Expense, Total							600
Two Thousand Twenty Two Loan Agreement [Member] \| Robert W. Duggan [Member]
Debt Instrument, Face Amount										$ 65,000
Debt Instrument Quarterly Interest Rate										5.0
Debt Instrument, Increase, Accrued Interest						$ 900
Insurance Loan Agreement [Member]
Debt Instrument, Face Amount	$ 1,900
Debt Instrument, Interest Rate, Stated Percentage	3.69%
Interest Expense, Total							$ 1

Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Basis of Accounting, Policy [Policy Text Block]

Basis of Presentation

Consolidation, Policy [Policy Text Block]

Principles of Consolidation

The accompanying consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and pursuant to the rules and regulations of the United States Securities Exchange Commission (the “SEC”). The consolidated financial statements include the financial statements of the Company and its wholly-owned subsidiaries and intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates, Policy [Policy Text Block]

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires the Company to make estimates that affect the amounts reported in the financial statements and accompanying notes to the financial statements. Estimates include, but are not limited to, the valuation and recognition of share-based compensation, inventory valuation, warranty obligations, income taxes, and the useful lives assigned to long-lived assets. The Company evaluates its estimates and assumptions based on historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ materially from these estimates.

Concentration Risk, Credit Risk, Policy [Policy Text Block]

Concentration of Credit Risk

Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents and investments. The Company places its cash equivalents and investments with high credit quality financial institutions and, by policy, limits the amounts invested with any one financial institution or issuer. Deposits held with banks may exceed the amount of insurance provided on such deposits. The Company has not experienced any losses since inception.

Fair Value of Financial Instruments, Policy [Policy Text Block]

Fair Value of Financial Instruments

The Company believes the carrying amounts of its financial instruments, including cash equivalents, prepaid expenses and other current assets, accounts payable and accrued expenses, approximate fair value due to the short-term nature of such instruments.

Cash and Cash Equivalents, Policy [Policy Text Block]

Cash and Cash Equivalents

The Company invests its cash primarily in money market funds. The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents.

Property, Plant and Equipment, Policy [Policy Text Block]

Property and Equipment

Property and Equipment is recorded at cost and depreciated using the straight-line method over their estimated useful lives, ranging from three to five years. Leasehold improvements are amortized using the straight-line method over the shorter of the lease term or estimated useful life. Upon the sale or retirement of property and equipment, the costs and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is reflected in operating expenses. Maintenance and repairs are charged to operations as incurred.

Inventory, Policy [Policy Text Block]

Valuation of Inventory

Inventory is stated at lower of cost or net realizable value. The Company establishes the inventory basis by determining the cost based on standard costs approximating the purchase costs on a first-in, first-out basis. Net realizable value is the estimated selling price in the ordinary course of the Company’s business, less reasonably predictable costs of completion, disposal, and transportation. The cost basis of the Company’s inventory will be reduced for any products that are considered excessive or obsolete based upon assumptions about future demand and market conditions. At December 31, 2022, the inventory balance has been fully written off due to excessive and obsolete inventory.

Goodwill and Intangible Assets, Intangible Assets, Policy [Policy Text Block]

Intangible Assets

The Company’s intangible assets consist of acquired patents and licenses, which are amortized over their estimated useful lives of twelve years.

Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]

Long-Lived Assets

The Company reviews long-lived assets, consisting of property and equipment and intangible assets, for impairment during each fiscal year or when events or changes in circumstances indicate the carrying value of these assets may exceed their current fair values. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the estimated undiscounted future cash flows expected to be generated by the asset. No impairment losses were incurred during the periods presented.

Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block]

Goodwill

The Company records goodwill when the consideration paid in a business acquisition exceeds the fair value of the net tangible assets and the identified intangible assets acquired. The Company reviews goodwill for impairment at the reporting unit level at least annually or whenever changes in circumstances indicate that the carrying value of the goodwill may not be recoverable. To date, there has been no impairment of goodwill.

Revenue from Contract with Customer [Policy Text Block]

Revenue from Contracts with Customers

The Company recognizes revenue at a point in time when it satisfies performance obligations by transferring control of promised goods to its customers. The amount of revenue recognized is equal to the consideration which the Company is entitled to in exchange for the promised goods, excluding any amounts assessed by government authorities for taxes which might be collected from a customer. Sales contracts often involve the sale and delivery of multiple products, each of which typically represent a separate performance obligation in the contract. While the Company sells these products on a stand-alone basis at their respective SSP, initial customer contracts will likely involve the bundling of products which will be delivered concurrently to the customer. In such instances, the full consideration of the contract will be recognized upon shipment of the products. The Company generally requires receipt of full payment prior to shipment, however, from time to time, payment terms may be extended to customers upon which the Company will perform a necessary credit evaluation to ensure future collectability of the outstanding balance. Refer to Note 9 for further details.

Standard Product Warranty, Policy [Policy Text Block]

Product Warranty

The Company provides a standard warranty on eligible products which provides the customer assurances that the products comply with the agreed-upon specifications. The standard warranty does not provide any services in addition to those assurances. The Company accrues a warranty reserve for products sold based upon the best estimate of the nature, frequency, and costs of future claims. These estimates are inherently uncertain given the short history of sales, and changes to the historical or projected warranty experience may cause material changes to the warranty reserve in the future. The warranty reserve is included within Accrued expenses on the consolidated balance sheets. Warranty expense is recorded as a component of Cost of Revenues in the consolidated statements of operations and comprehensive loss.

Warranty accrual activity consisted of the following (in thousands):

	*Year Ended December 31,*
	*2022*			*2021*
Beginning balance	$	80		$	—
Add: Accruals for warranties issued during the period		42			80
Less: Adjustment for inventory at cost and excessive and obsolete inventory		(72	)		—
Ending balance	$	50		$	80

Share-Based Payment Arrangement [Policy Text Block]

Stock-Based Compensation

The Company recognizes the cost of stock-based compensation in the financial statements based upon fair value. The fair value of stock options is determined as of the grant date using the Black-Scholes option pricing model. The fair value of Restricted Stock Units (“RSU”) awards is determined based on the number of units granted and the closing price of the Company’s common stock on the grant date. The fair value of each purchase under the employee stock purchase plan (“ESPP”) is estimated at the beginning of the offering period using the Black-Scholes option pricing model. The Company’s determination of the fair value of equity-settled awards is impacted by the price of the Company’s common stock as well as changes in assumptions regarding a number of complex and subjective variables. These variables include, but are not limited to, the expected term that awards will remain outstanding, expected common stock price volatility over the term of the awards, risk-free interest rates and expected dividends. The fair value of an award is recognized over the period during which service is required to be performed in exchange for the award, the requisite service period (usually the vesting period) on a straight-line basis. The Company accounts for all equity instruments awarded to non-employees at the fair value of the award issued on the day of the grant. The fair value of these equity instruments are expensed over the requisite service period. Certain stock options awarded to the Company’s executives and other key employees contain performance conditions related to certain financial measures and achievements of strategic/operational milestones (“performance options”). These performance options can contain both service and performance-based vesting conditions. The fair value of these performance options is recognized using the graded vesting method over the requisite service period beginning in the period in which the awards are deemed probable to vest, to the extent such awards are probable to vest.

Estimates of the fair value of equity-settled awards as of the grant date using valuation models, such as the Black-Scholes option pricing model, are affected by assumptions regarding a number of complex variables. Changes in the assumptions can materially affect the fair value of the award and the stock-based compensation expense recognized. These inputs are subjective and generally require significant analysis and judgment to develop. The Company determines the volatility factor based on its own historical volatility. The risk-free interest rate is based on the yield available on U.S. Treasury zero-coupon issues similar in duration to the expected term of the equity-settled award. For all stock options granted to date, the Company used the simplified method to calculate the expected term, which is the average of the contractual term and vesting period.

See Note 6 for a detailed discussion of the Company’s stock plans and stock-based compensation expense.

Research and Development Expense, Policy [Policy Text Block]

Research and Development Costs

Research and development costs consist primarily of compensation costs, fees paid to consultants and outside service providers and organizations (including university research institutes), costs associated with clinical trials, development prototypes and other expenses relating to the acquisition, design, development and testing of the Company’s product candidates, and certain facilities related costs. Research and development costs incurred by the Company are expensed as incurred, unless the achievement of milestones, the completion of contracted work, or other information indicates that a different expensing schedule is more appropriate.

Patent Costs [Policy Text Block]

Patent Costs

The Company is the owner of numerous domestic and foreign patents. Due to the significant uncertainty associated with the successful development of one or more commercially viable products based on the Company’s research efforts and any related patent applications, patent costs not related to acquired patents, including patent-related legal fees, filing fees and other costs, including internally generated costs, are expensed as incurred. During the years ended December 31, 2022, 2021 and 2020, patent costs totaled $0.5 million, $0.6 million and $0.5 million, respectively. Patent costs are included in general and administrative costs in the consolidated statements of operations and comprehensive loss.

Income Tax, Policy [Policy Text Block]

Income Taxes

The Company accounts for income taxes under an asset and liability approach for financial accounting and reporting for income taxes. Accordingly, the Company recognizes deferred tax assets and liabilities for the expected impact of differences between the financial statements and the tax basis of assets and liabilities.

The Company records a valuation allowance to reduce its deferred tax assets to the amount that is more-likely-than-not to be realized. In the event the Company determines that it would be able to realize its deferred tax assets in the future in excess of its recorded amount, an adjustment to the deferred tax assets would be credited to operations in the period such determination was made. Likewise, should the Company determine that it would not be able to realize all or part of its deferred tax assets in the future, an adjustment to the deferred tax assets would be charged to operations in the period such determination was made.

The Company is subject to U.S. federal income taxes and state income taxes in various states. As the Company’s net operating losses have yet to be utilized, previous tax years remain open to examination by federal authorities and other jurisdictions in which the Company currently operates or has operated in the past. The Company is not currently under examination by any tax authority.

The Company accounts for uncertainties in income tax law under a comprehensive model for the financial statement recognition, measurement, presentation and disclosure of uncertain tax positions taken or expected to be taken in income tax returns as prescribed by U.S. GAAP. The tax effects of a position are recognized only if it is more-likely-than-not to be sustained by the taxing authority as of the reporting date. If the tax position is not considered more-likely-than-not to be sustained, then no benefits of the position are recognized. At December 31, 2022 and 2021, the Company had not recorded any liability for uncertain tax positions. The Company includes interest and penalties related to uncertain tax positions as a component of income tax expense.

Comprehensive Income, Policy [Policy Text Block]

Comprehensive Loss

Comprehensive loss consists of net loss and unrealized gains or losses on available-for-sale investments. The Company displays comprehensive loss and its components as part of the consolidated statements of operations and comprehensive loss.

Earnings Per Share, Policy [Policy Text Block]

Net Loss per Share

The Company calculates basic net loss per share by dividing net loss by the weighted average number of shares of common stock outstanding during the period. Diluted net loss per share is computed by giving effect to all potential dilutive common stock equivalents outstanding during the period. For purposes of this calculation, options to purchase common stock and common stock warrants are considered common stock equivalents. Potential common shares that have an anti-dilutive effect (i.e., those that increase income per share or decrease loss per share) are excluded from the calculation of diluted net loss per share.

The following outstanding stock options, warrants, and RSUs to purchase common stock were excluded from the computation of diluted net loss per share for the periods presented because including them would have had an anti-dilutive effect:

	*Year Ended December 31,*
	*2022*		*2021*		*2020*
Common stock warrants		7,303,832		—		612,310
Common stock options		5,250,696		5,996,813		5,039,194
Restricted stock units		—		—		111,305
Total		12,554,528		5,996,813		5,762,809

Segment Reporting, Policy [Policy Text Block]

Segment and Geographical Information

The Company operates in one segment and reports segment information in accordance with ASC 280, Segment Reporting. Management uses one measurement of profitability and does not segregate its business for internal reporting, however in making certain operating decisions and assessing performance, management will additionally review the disaggregated revenue results by product and geography. The Company’s Chief Executive Officer acts as the chief operating decision makers (“CODM”) of the Company. As of December 31, 2022 and 2021, 100% of long-lived assets were in the United States. Revenue is attributed to a geographic region based on the location of the end customer.

See Note 10 for details of revenue by product and geography.

New Accounting Pronouncements, Policy [Policy Text Block]

Recent Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers, requiring an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. This updated standard became effective for the Company in the first quarter of fiscal year 2018. The Company began to recognize revenue in 2021 using this updated standard. See Note 9 for additional details of the revenue recognition approach.

In November 2018, the FASB issued ASU No. 2018-18 Collaborative Arrangements – Clarifying the Interaction between Topic 808 (Collaborative Arrangements) and Topic 606 (Revenue from Contracts with Customers), which clarifies the interaction between ASC 808, Collaborative Arrangements and ASC 606, Revenue from Contracts with Customers (“ASC 606”). The ASU clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC 606 when the counterparty is a customer. In addition, the ASU precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue if the counterparty is not a customer for that transaction. The Company adopted the standard on January 1, 2020, however, did not record revenue until August 2021 and does not currently have any collaborative arrangements in place. The adoption of the new standard had no impact on the Company’s consolidated financial statements.

In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which eliminates certain exceptions related to the general principles in ASC 740 and makes amendments to other areas with the intention of simplifying various aspects related to accounting for income taxes. The new standard is effective for fiscal years beginning after December 15, 2020, including interim periods therein; with early adoption permitted. The Company adopted the Topic 740 effective January 1, 2021. The adoption did not have a material impact on the Company’s financial statements.

Note 12 - Related Party Transactions (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended		12 Months Ended
	Sep. 20, 2022	Jun. 30, 2021	Jul. 31, 2021	Jun. 30, 2021	May 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	May 13, 2021	May 11, 2021
Common Stock, Par or Stated Value Per Share (in dollars per share)						$ 0.001	$ 0.001
Proceeds from Issuance of Common Stock						$ 14,864	$ 56,697	$ 29,434
Board of Directors Chairman [Member] \| Letter Agreement [Member]
Related Party Transaction, Amounts of Transaction						$ 600
Board of Directors Chairman [Member] \| Conversion of Loan Agreement into Common Stock [Member]
Debt Conversion, Original Debt, Amount				$ 41,000
Board of Directors Chairman [Member] \| Private Placement [Member]
Stock Issued During Period, Shares, New Issues (in shares)		3,048,780
Common Stock, Par or Stated Value Per Share (in dollars per share)		$ 0.001		$ 0.001
Shares Issued, Price Per Share (in dollars per share)		$ 16.40		$ 16.40
Stock Issued During Period, Value, New Issues		$ 50,000
Proceeds from Issuance of Common Stock		8,400	$ 8,400
Board of Directors Chairman [Member] \| Private Placement [Member] \| Conversion of Loan Agreement into Common Stock [Member]
Debt Conversion, Original Debt, Amount		41,000
Board of Directors Chairman [Member] \| Loan Agreement [Member]
Debt Instrument, Face Amount									$ 41,000	$ 41,000
Long-Term Debt, Total		$ 0		$ 0
Robert W. Duggan [Member] \| Letter Agreement [Member]
Directors and Officers Liability Insurance, Period (Year)						1 year
Due to Related Parties, Total						$ 1,000
Related Party Transaction, Amounts of Transaction	$ 65,000
Robert W. Duggan [Member] \| Letter Agreement [Member] \| Subsequent Event [Member]
Directors and Officers Liability Insurance, Period (Year)					1 year

Note 10 - Segment Reporting

12 Months Ended

Dec. 31, 2022

Segment Reporting Disclosure [Text Block]

10. Segment Reporting

The Company operates and manages the business as one reportable and operating segment. The Company’s Chief Executive Officer acts as the chief operating decision maker ("CODM") of the Company. The CODM reviews the results of the Company on a consolidated basis, however in making certain operating decisions and assessing performance, the CODM will additionally review the disaggregated revenue results by product and geography. All of the Company’s long-lived assets are based in the United States.

Revenue by product consisted of the following (in thousands):

	*Year Ended December 31,*
	*2022*		*2021*		*2020*
Systems	$	560	$	1,189	$	—
Cycle units		140		229		—
Total consolidated revenue	$	700	$	1,418	$	—

Revenue by geography consisted of the following (in thousands):

	*Year Ended December 31,*
	*2022*		*2021*		*2020*
North America	$	517	$	1,182	$	—
Rest of World		183		236		—
Total consolidated revenue	$	700	$	1,418	$	—

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8924-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8981-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8721-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9031-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (f)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (e)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 26
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8844-108599

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9038-108599

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9054-108599

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 15
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8657-108599

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8721-108599

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-URI https://asc.fasb.org/topic&trid=2134510

Note 6 - Stockholders' Equity and Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Thousands							1 Months Ended								7 Months Ended	12 Months Ended
	Jun. 09, 2022	Jun. 30, 2021	Jun. 01, 2021	Feb. 05, 2021	Jan. 01, 2021	Jun. 01, 2019	Oct. 31, 2021	Jul. 31, 2021	Jun. 30, 2021	May 31, 2021	Mar. 31, 2021	Jun. 30, 2020	Dec. 31, 2017	Nov. 30, 2017	Feb. 04, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2017	Nov. 30, 2021	Dec. 31, 2016	Dec. 31, 2014
Preferred Stock, Shares Authorized (in shares)																50,000,000	50,000,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)																$ 0.001	$ 0.001
Preferred Stock, Shares Outstanding, Ending Balance (in shares)																0	0
Common Stock, Shares Authorized (in shares)																500,000,000	500,000,000
Common Stock, Par or Stated Value Per Share (in dollars per share)																$ 0.001	$ 0.001
Proceeds from Issuance of Common Stock																$ 14,864	$ 56,697	$ 29,434
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)																$ 2.05	$ 0
Class of Warrant or Right, Exercised During Period (in shares)																13,240
Class of Warrant or Right, Outstanding (in shares)																7,303,832	0
Proceeds from Warrant Exercises																$ 26	$ 4,217	244
Share-Based Payment Arrangement, Expense																5,191	14,601	10,075
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total																$ 5,600
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)																2 years 3 months
Time-based Options [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period, Intrinsic Value																	800	1,600
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Intrinsic Value																$ 2,300	15,100	6,700
Share-Based Payment Arrangement, Expense																$ 4,467	9,235	8,739
Time-based Options [Member] \| Share-Based Payment Arrangement, Tranche One [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage																25.00%
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)																1 year
Performance Options [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Intrinsic Value																$ 800	2,500	5,500
Share-Based Payment Arrangement, Expense																233	4,840	133
Restricted Stock Units (RSUs) [Member]
Share-Based Payment Arrangement, Expense																0	0	86
Restricted Stock Units (RSUs) [Member] \| Granted in 2017 [Member] \| Share-Based Payment Arrangement, Employee [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)													68,800
Share-Based Payment Arrangement, Expense																0	$ 100	$ 300
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total																0
Restricted Stock Units (RSUs) [Member] \| Share-Based Payment Arrangement, Tranche One [Member] \| Granted in 2017 [Member] \| Share-Based Payment Arrangement, Employee [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage						50.00%
Restricted Stock Units (RSUs) [Member] \| Share-Based Payment Arrangement, Tranche Two [Member] \| Granted in 2017 [Member] \| Share-Based Payment Arrangement, Employee [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage			50.00%
Modified Performance Options [Member]
Share-Based Payment Arrangement, Expense																$ 4,100
The 2017 Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)																			10 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)													1,500,000						1,500,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares)																1,188,657	1,022,002
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Number of Shares (in shares)													1,200,000						1,200,000
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Percent													4.00%						4.00%
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)																2,368,716
The 2017 Inducement Equity Incentive Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)														10 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)														1,000,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares)										1,000,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)																1,053,767
The 2017 Inducement Equity Incentive Plan [Member] \| Share-Based Payment Arrangement, Tranche One [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage														25.00%
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)														1 year
The 2017 Employee Stock Purchase Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)													250,000						250,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares)					383,250
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Number of Shares (in shares)													450,000						450,000
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Percent													1.50%						1.50%
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)																460,999
Stock Issued During Period, Shares, Employee Stock Purchase Plans (in shares)																188,097	91,378
Board of Directors Chairman [Member] \| Loan Agreement [Member]
Long-Term Debt, Total		$ 0							$ 0
Board of Directors Chairman [Member] \| Conversion of Loan Agreement into Common Stock [Member]
Debt Conversion, Original Debt, Amount									$ 41,000
Chief Executive Officer [Member] \| Restricted Stock Units (RSUs) [Member] \| Granted in 2017 [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)													160,974
Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Outstanding, Number, Ending Balance (in shares)																0
Share-Based Payment Arrangement, Expense																$ 0
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total																0
Former Director [Member] \| The 2017 Plan [Member] \| Share-Based Payment Arrangement, Option [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)							10 years
Share-Based Payment Arrangement, Expense																$ 1,400
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period Upon Resignation (Day)							90 days
Maximum [Member] \| The 2017 Inducement Equity Incentive Plan [Member] \| Share-Based Payment Arrangement, Option [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)														10 years
Rights Offering Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)	1
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)												641,571				7,317,072
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 2.05											$ 7.01				$ 2.05
Warrants and Rights Outstanding, Term (Year)	5 years											5 years				5 years
Class of Warrants or Rights, Redemption Price Per Share (in dollars per share)	$ 0.01			$ 0.01												$ 0.01		$ 0.01
Class of Warrant or Right, Period of Written Notice for Exercise (Year)	30 years											30 days				30 years
Class of Warrant or Right, Percentage Required for Redemption	200.00%											200.00%				200.00%
Class of Warrant or Right, Exercise, Consecutive Trading Days (Year)	20 years											10 days				20 years
Period of Time Warrants Are Not Able to Be Redeemed (Month)	3 months											6 months
Class of Warrant or Right, Exercised During Period (in shares)				5,139											636,432	13,240
Class of Warrant or Right, Outstanding (in shares)																0	7,303,832
Proceeds from Warrant Exercises															$ 4,500
Rights Offering Warrants [Member] \| Maximum [Member]
Additional Proceeds That May be Received Upon Exercise of Warrants	$ 15,000
Private Placement Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)																						299,625
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)																						$ 2.67
Warrants and Rights Outstanding, Term (Year)																						7 years
Class of Warrant or Right, Exercised During Period (in shares)											45,638
Stock Issued During Period, Shares, Exercise of Warrants (in shares)											40,563
Class of Warrant or Right, Unexercised and Expired (in shares)																				600
Class of Warrant or Right, Outstanding (in shares)																0
IPO Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)																					574,985
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)																					$ 5.00
Warrants and Rights Outstanding, Term (Year)																					5 years
Class of Warrant or Right, Exercised During Period (in shares)											85,385
Stock Issued During Period, Shares, Exercise of Warrants (in shares)											68,958
Class of Warrant or Right, Outstanding (in shares)																0
Rights Offering [Member]
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.001											$ 0.001
Equity Offering, Units, Sale of Units (in shares)	7,317,072
Shares Issued, Price Per Share (in dollars per share)	$ 2.05
Number of Shares Per Unit Issued (in shares)	1
Number of Warrants Per Unit (in shares)	1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)	1
Stock Issued During Period, Shares, New Issues (in shares)	7,317,072
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)	7,317,072
Proceeds from Issuance of Common Stock	$ 15,000
Rights Offering [Member] \| Board of Directors Chairman [Member]
Investment Owned, Percent of Net Assets	56.00%
Private Placement [Member] \| Board of Directors Chairman [Member]
Common Stock, Par or Stated Value Per Share (in dollars per share)		$ 0.001							$ 0.001
Shares Issued, Price Per Share (in dollars per share)		$ 16.40							$ 16.40
Stock Issued During Period, Shares, New Issues (in shares)		3,048,780
Proceeds from Issuance of Common Stock		$ 8,400						$ 8,400
Private Placement [Member] \| Board of Directors Chairman [Member] \| Conversion of Loan Agreement into Common Stock [Member]
Debt Conversion, Original Debt, Amount		$ 41,000
ATM Offering [Member]
Shares Issued, Price Per Share (in dollars per share)																	$ 27.73
Stock Issued During Period, Shares, New Issues (in shares)																	288,490
Proceeds from Issuance of Common Stock																	$ 7,400
Equity Offering, Maximum Offering Amount															$ 60,000

Note 6 - Stockholders' Equity and Stock-based Compensation - Stock-based Compensation Expense by Type (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Total stock-based compensation expense	$ 5,191	$ 14,601	$ 10,075
Time-based Options [Member]
Total stock-based compensation expense	4,467	9,235	8,739
Performance Options [Member]
Total stock-based compensation expense	233	4,840	133
Restricted Stock Units (RSUs) [Member]
Total stock-based compensation expense	0	0	86
Employee Stock Purchase Plan Award [Member]
Total stock-based compensation expense	$ 491	$ 526	$ 1,117

Note 8 - Controlled Launch (Details Textual) $ in Thousands	12 Months Ended
Note 8 - Controlled Launch (Details Textual) $ in Thousands	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Feb. 28, 2021
Number of KOLs				70
Controlled Launch, Program Expenses	$ 100	$ 1,800
Revenue from Contract with Customer, Excluding Assessed Tax	700	1,418	$ 0
Redemption of Non Cash Credits [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 400	$ 1,100
Minimum [Member]
Number of Patients Participating in Procedure				40
Maximum [Member]
Number of Patients Participating in Procedure				50

Note 14 - Restructuring Charges

12 Months Ended

Dec. 31, 2022

Restructuring and Related Activities Disclosure [Text Block]

14. Restructuring Charges

On March 31, 2022, the Company initiated a plan to reduce its operating expenses, preserve financial resources, and focus its sales and marketing efforts on increasing utilization of CellFX Systems. The Company’s Board of Directors approved changes to the Company’s commercial leadership, restructuring of its commercial field organization and reductions in other personnel and expenses across the Company. The Company announced a reduction in force effective as of March 31, 2022. The affected employees were offered separation benefits, including severance payments along with temporary healthcare coverage assistance. The Company incurred a discrete restructuring related charge of $0.7 million which was fully recorded in March 2022 and the related expenses are included within total cost and expenses on the consolidated statement of operations for the year ended December 31, 2022. This charge represents the total amount to be incurred in connection with the activity. During the year ended December 31, 2022, the Company paid the entire $0.7 million.

On September 20, 2022, the Company initiated an additional reduction in force to align its workforce with its shift in strategic direction to advance its core NPS technology outside of dermatology. The reduction primarily impacted dermatological sales, marketing and other related support personnel. The affected employees were offered separation benefits, including severance payments along with temporary healthcare coverage assistance. The Company incurred a discrete restructuring related charge of $0.2 million which was fully recorded in September 2022 and the related expenses are included within total cost and expenses on the consolidated statement of operations for the year ended December 31, 2022. During the year ended December 31, 2022, the Company paid the entire $0.2 million.

Note 14 - Restructuring Charges (Details Textual) - Employee Severance [Member] - USD ($) $ in Millions	1 Months Ended
	Sep. 30, 2022	Mar. 31, 2022
March 2022 Restructuring Plan [Member]
Payments for Restructuring		$ 0.7
September 2022 Restructuring Plan [Member]
Payments for Restructuring	$ 0.2
Total Cost and Expenses [Member] \| March 2022 Restructuring Plan [Member]
Restructuring Charges, Total		$ 0.7
Total Cost and Expenses [Member] \| September 2022 Restructuring Plan [Member]
Restructuring Charges, Total	$ 0.2

Note 4 - Balance Sheet Components - Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Raw materials	$ 0	$ 2,010
Work in process	0	1,371
Finished goods	0	2,443
Total inventory	$ 0	$ 5,824

Note 6 - Stockholders' Equity and Stock-based Compensation - Stock-based Compensation Expense by Recorded Location (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Total stock-based compensation expense	$ 5,191	$ 14,601	$ 10,075
Cost of Sales [Member]
Total stock-based compensation expense	217	129	0
Research and Development Expense [Member]
Total stock-based compensation expense	1,563	5,211	4,013
Selling and Marketing Expense [Member]
Total stock-based compensation expense	733	2,749	1,187
General and Administrative Expense [Member]
Total stock-based compensation expense	$ 2,678	$ 6,512	$ 4,875

Note 9 - Revenue

12 Months Ended

Dec. 31, 2022

Revenue from Contract with Customer [Text Block]

9. Revenue

The Company recognizes revenue at a point in time when it satisfies performance obligations by transferring control of promised goods to its customers. The amount of revenue recognized is equal to the consideration which the Company is entitled to in exchange for the promised goods, excluding any amounts assessed by government authorities for taxes which might be collected from a customer. This consideration may include non-cash services performed, as is the case with revenue recognized in connection with the Controlled Launch program. On September 20, 2022, the Company announced its shift in focus to advance its core NPS technology outside of dermatology and concluded its Controlled Launch program. Total revenue recognized for the years ended December 31, 2022 and 2021 was $0.7 million and $1.4 million, respectively, of which approximately $0.4 million and $1.1 million, respectively, was driven by the redemption of non-cash credits earned as part of the Controlled Launch, with the balances driven by cash purchases of cycle units (“CUs”) and CellFX commercial consoles sold.

Sales contracts often involve the sale and delivery of multiple performance obligations in the contract.

Performance Obligations

Systems consist of the CellFX console and its embedded software, handpieces, and disposable tips. The console is a physical piece of hardware used by the customer to perform patient procedures. Individually the console and software are not distinct, therefore the Company combines the console and embedded software to form one distinct system performance obligation. Payment for systems is generally due prior to shipment, and the system performance obligation is satisfied upon shipment of the system to the customer.

Handpieces are attached to the console and used in conjunction with tips to perform patient procedures. Generally, upon initial sale of a system to a customer, the Company will include two handpieces. The handpiece has a shorter expected useful life than the console, and a customer can purchase additional handpieces when needed, as they are available for sale on a stand-alone basis. Payment for handpieces is generally due prior to shipment, and handpieces represent a distinct performance obligation which is satisfied either upon shipment, or upon delivery of the handpiece to the customer, depending on the specific contract.

Disposable treatment tips are single-patient multiple-use products that come in different sizes, each of which are to be used for specific procedures. Tips are attached to the handpiece for use in patient procedures and, upon detachment from the handpiece, a tip cannot be reused, and it must be disposed of. Tips represent a distinct performance obligation which is satisfied either upon shipment, or upon delivery of the tips to the customer, depending on the specific contract.

CUs are credits that authorize the customer to perform a procedure, or cycle. Each procedure requires a specific number of CUs, dependent upon type of tip used and procedure level selected. As the procedure is performed, the applicable number of CUs are decremented. When the customer’s balance of CUs on a specific system is depleted, the system will no longer function until the customer purchases additional CUs. Customers can purchase additional CUs via the Company’s CellFX Marketplace which is an online marketplace accessible directly from the CellFX System. Payment for CUs is due upon order placement and the CUs are immediately available for download to the console via CellFX CloudConnect. CUs represent a distinct performance obligation which is satisfied when CUs are made available for customers to download from the Company’s CellFX CloudConnect, as customers can use purchased CUs at any time at their discretion, and the Company does not provide any ongoing service or other forms of involvement after the sale occurs.

Shipping and handling activities are not considered to be a separate performance obligation. The Company’s standard commercial agreements generally include FOB shipping point terms. The Company has made an accounting policy election to account for shipping and handling costs as fulfillment costs because the shipping and handling activities occur after the customer obtains control of the product.

Transaction Price

The transaction price is the consideration to which the Company expects to be entitled to in exchange for providing the promised goods to customers. Customer orders placed for cash contemplate a fixed amount of consideration. Customer orders placed by physicians participating in the Controlled Launch when they elected to purchase the CellFX System were paid for via conversion of accumulated earned credits for prior services provided by the physicians under the terms of their participation in the Controlled Launch. For these transactions, the transaction price included noncash consideration. The services rendered by the physicians in the Controlled Launch were accounted for separately from the subsequent sales of the CellFX Systems because they were distinct from the system sales. They were distinct because they provided the Company with treatment data that could also be procured, and historically had been procured by the Company, without the corresponding system sales. This data was used by the Company to enhance marketing and promotion of its products.

The Company evaluates the possible impact of variable consideration in determining the transaction price, in particular the possibility of future returns or credits. Sales agreements allow for a right of return only if the product does not conform to the agreed upon quality standards or if the product was shipped due to Company error. The Company anticipates such returns will be minimal and has made no adjustments to the transaction price for any estimated returns. The transaction price is determined at the time of the initial revenue recognition and updated each quarter for any changes in circumstances (e.g., changes in estimated return or credit rates).

The Company has made an accounting policy election to exclude from the measurement of the transaction price all taxes which are imposed on and concurrent with a specific revenue-producing transaction and collected by the entity from a customer.

When there are multiple performance obligations present, the total transaction price shall be allocated to each of the performance obligations based upon the relative SSPs of those performance obligations. The Company establishes SSPs based on multiple factors including, prices charged by the Company for similar offerings, product-specific business objectives, and the estimated cost to provide the performance obligation. However, upon the sale of a new CellFX System, all performance obligations are delivered concurrently and therefore there is no impact to revenue recognition timing, and the Company has determined allocations are not necessary. Should the customer purchase additional CUs, handpieces, or tips at a later time, those purchases will be made under separate purchase agreements, with all promised goods generally transferred at the same time, therefore no price allocation is necessary in that scenario either.

Controlled Launch Agreements

In August 2021 the Company began to recognize revenue in relation to the conversion of Controlled Launch Program participants into sales agreements (Note 8). These customers were already in possession of the system, handpiece, and tips. As such, upon execution of these purchase agreements, the Company recognized revenue on the agreements because control of all performance obligations were transferred at that time. These customers separately purchased CUs in order to operate the CellFX System and the revenue for these CUs was recognized upon delivery of the CUs to CellFX CloudConnect.

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-URI https://asc.fasb.org/topic&trid=49130388

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130551-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(2)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130556-203045

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130554-203045

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 9
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130550-203045

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (e)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130554-203045

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130554-203045

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130554-203045

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 15
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130558-203045

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130554-203045

Note 7 - Research Grants and Agreements

12 Months Ended

Dec. 31, 2022

Research, Development, and Computer Software Disclosure [Text Block]

7. Research Grants and Agreements

Sponsored Research Agreement

The Company entered into a SRA with ODURF during 2014 pursuant to which the Company sponsors research activities performed by ODURF’s Frank Reidy Center. ODURF is compensated by the Company for its conduct of each study in accordance with the budget and payment terms set forth in the applicable task order. In August 2018, we agreed to sponsor a task order for research in the amount of $0.8 million and in September 2019, we agreed to sponsor an additional task order for research in the amount of $0.8 million each to be performed during their respective subsequent 12-month periods. In March 2021, we agreed to sponsor a task order for research in the amount of $0.3 million and in May 2021 we sponsored an additional task order for $0.3 million each to be performed during their respective subsequent 12-month periods. These sponsored researches are funded through monthly payments made upon ODURF certifying, to our reasonable satisfaction, that ODURF has met its obligations pursuant to the specified task order and statement of work. The principal investigator may transfer funds within the budget as needed with our approval so long as the obligations of ODURF under the task order and statement of work remain unchanged and unimpaired. During the years ended December 31, 2022, 2021 and 2020, we incurred costs relating to the SRA equal to $0.2 million, $0.3 million and $0.6 million, respectively. As of December 31, 2022, there are no unbilled SRAs left under the task orders.

Note 3 - Investments and Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2022

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

		*December 31, 2022*
Assets	*Classification*	*Level 1*		*Level 2*		*Level 3*		*Total*
Money market funds	Cash and cash equivalents	$	57,973	$	—	$	—	$	57,973
Total assets measured at fair value		$	57,973	$	—	$	—	$	57,973

		*December 31, 2021*
Assets	*Classification*	*Level 1*		*Level 2*		*Level 3*		*Total*
Money market funds	Cash and cash equivalents	$	23,675	$	—	$	—	$	23,675
Total assets measured at fair value		$	23,675	$	—	$	—	$	23,675

Note 13 - Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2022

Schedule of Information Related to Right-of-use Assets and Lease Liabilities [Table Text Block]

	Year Ended December 31,
Assets:	2022		2021
Right-of-use assets	$	8,062	$	8,785

	Year Ended December 31,
Liabilities:	2022		2021
Current operating lease liabilities	$	896	$	774
Non-current operating lease liabilities		9,144		10,040
Total lease liabilities	$	10,040	$	10,814

	*Year Ended December 31,*
	*2022*		*2021*		*2020*
Cash paid for operating lease liabilities	$	1,806	$	1,643	$	1,045

Year ending December 31:
2023	$	1,845
2024		1,910
2025		1,977
2026		2,046
2027		2,117
Thereafter		4,074
Total lease payments		13,969
Less imputed interest		(3,929	)
Total lease liabilities	$	10,040

Weighted-average remaining lease term			6.83
Weighted-average discount rate			10	%

Note 2 - Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Antidilutive securities (in shares)	12,554,528	5,996,813	5,762,809
Warrant [Member]
Antidilutive securities (in shares)	7,303,832	0	612,310
Share-Based Payment Arrangement, Option [Member]
Antidilutive securities (in shares)	5,250,696	5,996,813	5,039,194
Restricted Stock Units (RSUs) [Member]
Antidilutive securities (in shares)	0	0	111,305

Note 5 - Goodwill

12 Months Ended

Dec. 31, 2022

Goodwill Disclosure [Text Block]

5. Goodwill

In 2014, the Company acquired three companies (the acquisitions) for aggregate consideration of $5.5 million. In accordance with ASC Topic 805, Business Combinations, the Company recorded goodwill of $2.8 million in connection with the acquisitions, which represents the excess of consideration paid over the fair value of net tangible and intangible assets acquired.

The Company reviews goodwill for impairment annually or whenever changes in circumstances indicate that the carrying amount of goodwill may not be recoverable. Based on the Company’s annual review as of December 31, 2022, the Company determined that its goodwill was not impaired.

Note 4 - Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Property and equipment, gross	$ 4,914	$ 4,858
Less: Accumulated depreciation and amortization	(2,953)	(2,396)
Property and equipment, net	1,961	2,462
Leasehold Improvements [Member]
Property and equipment, gross	2,519	2,519
Laboratory Equipment [Member]
Property and equipment, gross	1,118	1,019
Furniture and Fixtures [Member]
Property and equipment, gross	966	932
Software and Software Development Costs [Member]
Property and equipment, gross	289	202
Construction in Progress [Member]
Property and equipment, gross	$ 22	$ 186

Note 10 - Segment Reporting - Revenue by Geography (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Total revenues	$ 700	$ 1,418	$ 0
North America [Member]
Total revenues	517	1,182	0
Rest of World [Member]
Total revenues	$ 183	$ 236	$ 0

Note 15 - Employee Benefit Plans

12 Months Ended

Dec. 31, 2022

Retirement Benefits [Text Block]

15. Employee Benefit Plans

The Company sponsors a defined contribution plan under which it may make discretionary contributions. The Company did not make any employer matching contributions to this plan during the years ended December 31, 2022, 2021 and 2020.

The entire disclosure for retirement benefits.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI https://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section S99
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=21916913&loc=d3e273930-122802

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (o)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (p)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-URI https://asc.fasb.org/topic&trid=2235017

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 60
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=6414203&loc=d3e39689-114964

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(03)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (q)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (r)(1)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(iii)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (l)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (r)(2)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Note 6 - Stockholders' Equity and Stock-based Compensation - Summary of Stock Option Activity (Details) - The 2015 Plan, 2017 Plan and Inducement Plan [Member] - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Options balances, number of shares (in shares)	5,996,813
Options balances, weighted average exercise price (in dollars per share)	$ 15.77
Options balances, weighted average remaining life (Year)	6 years 2 months 26 days	7 years 3 months 29 days
Options granted, number of shares (in shares)	1,440,100
Options granted, weighted average exercise price (in dollars per share)	$ 2.97
Options exercised, number of shares (in shares)	0
Options exercised, weighted average exercise price (in dollars per share)	$ 0
Options canceled, number of shares (in shares)	(1,472,385)
Options canceled, weighted average exercise price (in dollars per share)	$ 14.88
Options expired, number of shares (in shares)	(713,832)
Options expired, weighted average exercise price (in dollars per share)	$ 14.62
Options balances, number of shares (in shares)	5,250,696	5,996,813
Options balances, weighted average exercise price (in dollars per share)	$ 12.67	$ 15.77
Options exercisable, number of shares (in shares)	3,479,531
Options exercisable, weighted average exercise price (in dollars per share)	$ 15.17
Options exercisable, weighted average remaining life (Year)	5 years 21 days

Note 11 - Income Taxes (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Unrecognized Tax Benefits, Ending Balance	$ 8,925	$ 5,140	$ 2,491	$ 1,470
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 10,800	$ 17,000
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2034
Domestic Tax Authority [Member]
Operating Loss Carryforwards	$ 199,900
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2035
Operating Loss Carryforwards, Not Subject to Expiration	$ 174,300
Tax Credit Carryforward, Amount	5,800
State and Local Jurisdiction [Member]
Operating Loss Carryforwards	204,600
Tax Credit Carryforward, Amount	$ 5,500

Note 11 - Income Taxes - Reconciliation of Unrecognized Tax Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Unrecognized tax benefits at beginning of year	$ 5,140	$ 2,491	$ 1,470
Increases related to current year tax positions	2,055	2,649	1,021
Increases related to prior year tax positions	1,730	0	0
Unrecognized tax benefits at beginning of year	$ 8,925	$ 5,140	$ 2,491

Note 2 - Summary of Significant Accounting Policies (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Finite-Lived Intangible Asset, Useful Life (Year)	12 years
Impairment, Long-Lived Asset, Held-for-Use, Total	$ 0
Goodwill, Impairment Loss	0
Liability for Uncertainty in Income Taxes, Noncurrent	$ 0	$ 0
Number of Operating Segments	1
Geographic Concentration Risk [Member] \| Assets, Total [Member] \| UNITED STATES
Concentration Risk, Percentage	100.00%	100.00%
General and Administrative Expense [Member]
Patent Costs	$ 500	$ 600	$ 500
Minimum [Member] \| Equipment [Member]
Property, Plant and Equipment, Useful Life (Year)	3 years
Maximum [Member] \| Equipment [Member]
Property, Plant and Equipment, Useful Life (Year)	5 years

Note 4 - Balance Sheet Components

12 Months Ended

Dec. 31, 2022

Supplemental Balance Sheet Disclosures [Text Block]

4. Balance Sheet Components

Inventory

Inventory consisted of the following (in thousands):

	*Year Ended December 31,*
	*2022*		*2021*
Raw materials	$	—	$	2,010
Work in process		—		1,371
Finished goods		—		2,443
Total inventory	$	—	$	5,824

Property and Equipment, net

Property and equipment, net consisted of the following (in thousands):

	*December 31,*
	*2022*			*2021*
Leasehold improvements	$	2,519		$	2,519
Laboratory equipment		1,118			1,019
Furniture, fixtures and equipment		966			932
Software		289			202
Construction in progress		22			186
		4,914			4,858
Less: Accumulated depreciation and amortization		(2,953	)		(2,396	)
	$	1,961		$	2,462

Depreciation expense for the years ended December 31, 2022, 2021 and 2020 was $0.7 million, $0.5 million, and $0.4 million, respectively.

Intangible Assets, net

Intangible assets primarily consist of a license to utilize certain patents, know-how and technology relating to the Company’s NPS for biomedical applications acquired from Old Dominion University Research Foundation (ODURF), Eastern Virginia Medical School (EVMS), and the University of Southern California. In addition, the Company entered into a sponsored research agreement (“SRA”) with Old Dominion University’s Frank Reidy Research Center for Bioelectrics, a leading research organization in the field, which includes certain intellectual property rights arising from the research. The Company is amortizing the intangible assets over an estimated useful life of 12 years.

Intangible assets, net consisted of the following (in thousands):

	*December 31,*
	*2022*			*2021*
Acquired patents and licenses	$	7,985		$	7,985
Less: Accumulated amortization		(5,434	)		(4,769	)
	$	2,551		$	3,216

A schedule of the amortization of intangible assets is as follows (in thousands):

Years ending December 31:
2023	$	665
2024		665
2025		665
2026		556
	$	2,551

Accrued Expenses

Accrued expenses consisted of the following (in thousands):

	*December 31,*
	*2022*		*2021*
Compensation expense	$	1,377	$	2,932
Controlled launch (Note 8)		—		534
Director and officer liability insurance (Note 12)		571		—
Clinical trial fees and costs		64		245
Professional fees		318		85
Warranty		50		80
Other		215		513
	$	2,595	$	4,389

Note 6 - Stockholders' Equity and Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2022

Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]

						*Weighted*
						*Average*
				*Weighted*		*Remaining*
	*Number of*			*Average*		*Contractual*
	*Shares*			*Exercise Price*		*Life (in Years)*
Warrants outstanding at December 31, 2021		—		$	—		—
Issued		7,317,072			2.05
Exercised		(13,240	)		2.05
Expired/Redeemed		—			—
Warrants outstanding and exercisable at December 31, 2022		7,303,832		$	2.05		4.43

Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	*Year Ended December 31,*
	*2022*		*2021*		*2020*
Cost of revenues	$	217	$	129	$	—
Research and development		1,563		5,211		4,013
Sales and marketing		733		2,749		1,187
General and administrative		2,678		6,512		4,875
Total stock-based compensation expense	$	5,191	$	14,601	$	10,075

Share-Based Payment Arrangement, Cost by Plan [Table Text Block]

	*Year Ended December 31,*
	*2022*		*2021*		*2020*
Time-based options	$	4,467	$	9,235	$	8,739
Performance options		233		4,840		133
RSU		—		—		86
ESPP		491		526		1,117
Total stock-based compensation expense	$	5,191	$	14,601	$	10,075

Share-Based Payment Arrangement, Option [Member]

Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	*Year Ended December 31,*
	*2022*	*2021*	*2020*
Expected term in years	5.3 - 6.8	5.3 - 6.1	5.3 - 6.1
Expected volatility	83 - 88%	78%	70%
Risk-free interest rate	1.9 - 3.2%	0.9 - 1.4%	0.3 - 0.5%
Dividend yield	—	—	—

Performance Options [Member]

Share-Based Payment Arrangement, Option, Activity [Table Text Block]

	*Stock Options Outstanding*
	*Number of shares*			*Weighted average exercise price*		*Weighted average remaining life (in years)*
Balances — December 31, 2021		1,200,097		$	13.11		8.44
Options granted		200,000			5.32
Options exercised		—			—
Options canceled		(797,920	)		13.32
Options expired		(81,875	)		11.28
Balances — December 31, 2022		520,302		$	10.08		7.02
Exercisable — December 31, 2022		248,861		$	12.25		4.92

Time-based Options [Member]

Share-Based Payment Arrangement, Option, Activity [Table Text Block]

	*Stock Options Outstanding*
	*Number of shares*			*Weighted average exercise price*		*Weighted average remaining life (in years)*
Balances — December 31, 2021		4,796,716		$	16.44		7.05
Options granted		1,240,100			2.59
Options exercised		—			—
Options canceled		(674,465	)		16.73
Options expired		(631,957	)		15.05
Balances — December 31, 2022		4,730,394		$	12.95		6.16
Exercisable — December 31, 2022		3,230,670		$	15.39		5.07

The 2017 Employee Stock Purchase Plan [Member]

Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	*Year Ended December 31,*
	*2022*	*2021*	*2020*
Expected term in years	0.5 - 1.0	0.5 - 1.0	0.5 - 1.0
Expected volatility	83%	78%	70	%
Risk-free interest rate	0.6% - 3.5%	0.06% - 0.1%	0.1% - 1.0%
Dividend yield	—	—	—

The 2015 Plan, 2017 Plan and Inducement Plan [Member]

Share-Based Payment Arrangement, Option, Activity [Table Text Block]

	*Stock Options Outstanding*
	*Number of shares*			*Weighted average exercise price*		*Weighted average remaining life (in years)*
Balances — December 31, 2021		5,996,813		$	15.77		7.33
Options granted		1,440,100			2.97
Options exercised		—			—
Options canceled		(1,472,385	)		14.88
Options expired		(713,832	)		14.62
Balances — December 31, 2022		5,250,696		$	12.67		6.24
Exercisable — December 31, 2022		3,479,531		$	15.17		5.06

Note 11 - Income Taxes (Tables)

12 Months Ended

Dec. 31, 2022

Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]

	*Year Ended December 31,*
	*2022*			*2021*			*2020*
Domestic	$	(58,505	)	$	(63,660	)	$	(49,851	)
Foreign		—			—			—
	$	(58,505	)	$	(63,660	)	$	(49,851	)

Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]

	*December 31,*
	*2022*		*2021*		*2020*
Current
Federal	$	—	$	—	$	—
State		3		3		3
Foreign		—		—		—
Total current		3		3		3

Deferred
Federal		—		—		—
State		—		—		—
Foreign		—		—		—
Total deferred		—		—		—

Total provision for income taxes	$	3	$	3	$	3

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

	*Year Ended December 31,*
	*2022*			*2021*			*2020*
Federal tax at statutory rate		21.0	%		21.0	%		21.0	%
State tax at statutory rate		8.4			8.4			8.4
Research and development credits		0.9			1.9			2.1
Change in valuation allowance		(18.4	)		(26.8	)		(43.3	)
Deferred adjustment		(5.3	)		—			8.5
Change in tax rate		—			—			4.2
Uncertain Tax Position		(5.7	)		(2.3	)		—
Other		(0.9	)		(2.2	)		(0.8	)
Provision for income taxes		—	%		—	%		—	%

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]

	*December 31,*
	*2022*			*2021*
Deferred tax assets
Accruals	$	3,404		$	1,034
Net operating loss carryforwards		56,447			49,246
Tax credit carryforwards		7,111			6,611
Stock-based compensation		8,784			12,188
R&D Capitalization		3,810			—
Lease liability under ASC 842		2,948			3,182
Gross deferred tax assets		82,504			72,261
Valuation allowance		(79,779	)		(69,006	)
Total deferred tax assets		2,725			3,255

Deferred tax liabilities
Intangibles		(117	)		(365	)
ROU asset under ASC 842		(2,593	)		(2,862	)
Fixed assets		(15	)		(28	)
Total deferred tax liabilities		(2,725	)		(3,255	)

Net deferred tax assets/(liabilities)	$	—		$	—

Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]

	*December 31,*
	*2022*		*2021*		*2020*
Unrecognized tax benefits at beginning of year	$	5,140	$	2,491	$	1,470
Increases related to current year tax positions		2,055		2,649		1,021
Increases related to prior year tax positions		1,730		—		—
Unrecognized tax benefits at end of year	$	8,925	$	5,140	$	2,491

Note 11 - Income Taxes

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Text Block]

11. Income Taxes

Income (loss) before income taxes (in thousands):

	*Year Ended December 31,*
	*2022*			*2021*			*2020*
Domestic	$	(58,505	)	$	(63,660	)	$	(49,851	)
Foreign		—			—			—
	$	(58,505	)	$	(63,660	)	$	(49,851	)

The components of the provision for income taxes are as follows (in thousands):

	*December 31,*
	*2022*		*2021*		*2020*
Current
Federal	$	—	$	—	$	—
State		3		3		3
Foreign		—		—		—
Total current		3		3		3

Deferred
Federal		—		—		—
State		—		—		—
Foreign		—		—		—
Total deferred		—		—		—

Total provision for income taxes	$	3	$	3	$	3

State income taxes are immaterial in amount and therefore have not been recorded in the Consolidated Statements of Operations and Comprehensive Loss for the years ended December 31, 2022, 2021 and 2020.

The provision for income taxes differs from the amount estimated by applying the statutory federal income tax rate to income (loss) before taxes as follows:

	*Year Ended December 31,*
	*2022*			*2021*			*2020*
Federal tax at statutory rate		21.0	%		21.0	%		21.0	%
State tax at statutory rate		8.4			8.4			8.4
Research and development credits		0.9			1.9			2.1
Change in valuation allowance		(18.4	)		(26.8	)		(43.3	)
Deferred adjustment		(5.3	)		—			8.5
Change in tax rate		—			—			4.2
Uncertain Tax Position		(5.7	)		(2.3	)		—
Other		(0.9	)		(2.2	)		(0.8	)
Provision for income taxes		—	%		—	%		—	%

Deferred income taxes reflect the impact of carryforwards and temporary differences between the amounts of assets and liabilities for financial reporting purposes and such amounts as measured by tax laws. The carryforwards and temporary differences, which give rise to a significant portion of the Company’s deferred tax asset (liability) as of December 31, 2022 and 2021, are as follows (in thousands):

	*December 31,*
	*2022*			*2021*
Deferred tax assets
Accruals	$	3,404		$	1,034
Net operating loss carryforwards		56,447			49,246
Tax credit carryforwards		7,111			6,611
Stock-based compensation		8,784			12,188
R&D Capitalization		3,810			—
Lease liability under ASC 842		2,948			3,182
Gross deferred tax assets		82,504			72,261
Valuation allowance		(79,779	)		(69,006	)
Total deferred tax assets		2,725			3,255

Deferred tax liabilities
Intangibles		(117	)		(365	)
ROU asset under ASC 842		(2,593	)		(2,862	)
Fixed assets		(15	)		(28	)
Total deferred tax liabilities		(2,725	)		(3,255	)

Net deferred tax assets/(liabilities)	$	—		$	—

The Company’s unrecognized tax benefits as of December 31, 2022, 2021 and 2020 were $8.9 million, $5.1 million, and $2.5 million, respectively. If recognized, none of the unrecognized tax benefits would impact income tax expense to the extent that the Company continues to maintain a full valuation allowance against its deferred tax assets.

A reconciliation of the beginning and ending amounts of unrecognized tax benefit is as follows (in thousands):

	*December 31,*
	*2022*		*2021*		*2020*
Unrecognized tax benefits at beginning of year	$	5,140	$	2,491	$	1,470
Increases related to current year tax positions		2,055		2,649		1,021
Increases related to prior year tax positions		1,730		—		—
Unrecognized tax benefits at end of year	$	8,925	$	5,140	$	2,491

The Company’s policy is to recognize interest and penalties related to income taxes as components of interest expense and other expense, respectively. The Company did not accrue interest and penalties related to unrecognized tax benefits as of December 31, 2022 and does not anticipate any significant change within twelve months of this reporting date.

The Company’s valuation allowance increased by $10.8 million in the year ended December 31, 2022 and increased by $17.0 million in the year ended December 31, 2021.

As of December 31, 2022, the Company had federal and state net operating loss (“NOL”) carryforwards of $199.9 million and $204.6 million, respectively, which begin to expire in 2034. Of the total federal NOL carryforward of $199.9 million, approximately $174.3 million is carried forward indefinitely but is limited to 80% of the taxable income.

As of December 31, 2022, the Company had approximately $5.8 million and $5.5 million of U.S. federal and California research and development (“R&D”) credits, respectively. The federal R&D credits begin to expire in 2035 and the California R&D credits have an indefinite carryforward period.

The Company is subject to taxation in the United States for Federal and for State, within various states in which the Company operates. All jurisdictions and tax years currently remain open for IRS and state taxing authorities’ examination. As of December 31, 2022, the Company was not under examination by the Internal Revenue Service or any state tax jurisdiction.

Internal Revenue Code Section 382 ownership change generally occurs if one or more stockholders or groups of stockholders who own at least 5% of our stock increase their ownership by more than 50 percentage points over their lowest ownership percentage within a rolling three-year period. Similar rules may apply under state tax laws. The Company is not aware of any ownership changes in this financial period ending on December 31, 2022.

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 21
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-URI https://asc.fasb.org/extlink&oid=122134291&loc=d3e330215-122817

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 17
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32809-109319

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-URI https://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 14
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 270
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI https://asc.fasb.org/topic&trid=2144680

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Note 10 - Segment Reporting (Tables)

12 Months Ended

Dec. 31, 2022

Disaggregation of Revenue [Table Text Block]

	*Year Ended December 31,*
	*2022*		*2021*		*2020*
Systems	$	560	$	1,189	$	—
Cycle units		140		229		—
Total consolidated revenue	$	700	$	1,418	$	—

Revenue from External Customers by Geographic Areas [Table Text Block]

	*Year Ended December 31,*
	*2022*		*2021*		*2020*
North America	$	517	$	1,182	$	—
Rest of World		183		236		—
Total consolidated revenue	$	700	$	1,418	$	—

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Rights Offering [Member] Common Stock [Member]	Rights Offering [Member] Additional Paid-in Capital [Member]	Rights Offering [Member] AOCI Attributable to Parent [Member]	Rights Offering [Member] Retained Earnings [Member]	Rights Offering [Member]	Private Placement [Member] Common Stock [Member]	Private Placement [Member] Additional Paid-in Capital [Member]	Private Placement [Member] AOCI Attributable to Parent [Member]	Private Placement [Member] Retained Earnings [Member]	Private Placement [Member]	ATM Offering [Member] Common Stock [Member]	ATM Offering [Member] Additional Paid-in Capital [Member]	ATM Offering [Member] AOCI Attributable to Parent [Member]	ATM Offering [Member] Retained Earnings [Member]	ATM Offering [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2019																20,825,000
Balance at Dec. 31, 2019																$ 21	$ 153,401	$ 4	$ (122,689)	$ 30,737
Issuance of common stock upon exercise of stock options (in shares)																175,000
Issuance of common stock upon exercise of stock options																$ 0	887	0	0	887
Issuance of shares under employee stock purchase plan (in shares)																83,000
Issuance of shares under employee stock purchase plan																$ 0	490	0	0	490
Issuance of shares upon exercise of warrants (in shares)																187,000
Issuance of shares upon exercise of warrants																$ 0	1,127	0	0	1,127
Issuance of common stock, shares (in shares)	4,280,000
Issuance of common stock	$ 4	$ 29,430	$ 0	$ 0	$ 29,434
Stock-based compensation expense																0	10,075	0	0	10,075
Unrealized gain (loss) on available-for-sale securities																0	0	(5)	0	(5)
Net loss																$ 0	0	0	(49,851)	(49,851)
Balance (in shares) at Dec. 31, 2020																25,550,000
Balance at Dec. 31, 2020																$ 25	195,410	(1)	(172,540)	22,894
Issuance of common stock upon exercise of stock options (in shares)																54,000
Issuance of common stock upon exercise of stock options																$ 0	616	0	0	616
Issuance of shares under employee stock purchase plan (in shares)																91,000
Issuance of shares under employee stock purchase plan																$ 0	810	0	0	810
Issuance of shares upon exercise of warrants (in shares)																585,000
Issuance of shares upon exercise of warrants																$ 1	3,333	0	0	3,334
Issuance of common stock, shares (in shares)											288,000				288,490
Issuance of common stock											$ 0	$ 7,432	$ 0	$ 0	$ 7,432
Stock-based compensation expense																0	14,601	0	0	14,601
Unrealized gain (loss) on available-for-sale securities																0	0	1	0	1
Net loss																$ 0	0	0	(63,660)	(63,660)
Issuance of common stock as part of debt extinguishment and private investment, net of issuance cost of $106 (in shares)						3,049,000
Issuance of common stock as part of debt extinguishment and private investment, net of issuance cost of $106						$ 3	$ 49,891	$ 0	$ 0	$ 49,894
Issuance of common stock upon vesting of restricted stock units, net of shares withheld for employee taxes (in shares)																99,000
Issuance of common stock upon vesting of restricted stock units, net of shares withheld for employee taxes																$ 0	(232)	0	0	(232)
Balance (in shares) at Dec. 31, 2021																29,716,000
Balance at Dec. 31, 2021																$ 29	271,861	0	(236,200)	35,690
Issuance of shares under employee stock purchase plan (in shares)																188,000
Issuance of shares under employee stock purchase plan																$ 1	485	0	0	486
Issuance of shares upon exercise of warrants (in shares)																14,000
Issuance of shares upon exercise of warrants																$ 0	26	0	0	26
Issuance of common stock, shares (in shares)	7,317,000
Issuance of common stock	$ 7	$ 14,857	$ 0	$ 0	$ 14,864
Stock-based compensation expense																0	5,191	0	0	5,191
Unrealized gain (loss) on available-for-sale securities																				0
Net loss																$ 0	0	0	(58,505)	(58,505)
Balance (in shares) at Dec. 31, 2022																37,235,000
Balance at Dec. 31, 2022																$ 37	$ 292,420	$ 0	$ (294,705)	$ (2,248)

Note 11 - Income Taxes - Deferred Tax Asset (Liability) (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Accruals	$ 3,404	$ 1,034
Net operating loss carryforwards	56,447	49,246
Tax credit carryforwards	7,111	6,611
Stock-based compensation	8,784	12,188
R&D Capitalization	3,810	0
Lease liability under ASC 842	2,948	3,182
Gross deferred tax assets	82,504	72,261
Valuation allowance	(79,779)	(69,006)
Total deferred tax assets	2,725	3,255
Intangibles	(117)	(365)
ROU asset under ASC 842	(2,593)	(2,862)
Fixed assets	(15)	(28)
Total deferred tax liabilities	(2,725)	(3,255)
Net deferred tax assets/(liabilities)	$ 0	$ 0

Note 6 - Stockholders' Equity and Stock-based Compensation - Option Assumptions (Details) - Share-Based Payment Arrangement, Option [Member]	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Expected volatility		78.00%	70.00%
Dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Expected term in years (Year)	5 years 3 months 18 days	5 years 3 months 18 days	5 years 3 months 18 days
Risk-free interest rate	1.90%	0.90%	0.30%
Maximum [Member]
Expected term in years (Year)	6 years 9 months 18 days	6 years 1 month 6 days	6 years 1 month 6 days
Risk-free interest rate	3.20%	1.40%	0.50%

Note 4 - Balance Sheet Components - Schedule of Amortization of Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
2023	$ 665
2024	665
2025	665
2026	556
Finite-Lived Intangible Assets, Net, Ending Balance	$ 2,551	$ 3,216

Note 2 - Summary of Significant Accounting Policies - Warrant Accrual Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Beginning balance	$ 80	$ 0
Add: Accruals for warranties issued during the period	42	80
Less: Adjustment for inventory at cost and excessive and obsolete inventory	(72)	0
Ending balance	$ 50	$ 80

Note 2 - Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2022

Schedule of Product Warranty Liability [Table Text Block]

	*Year Ended December 31,*
	*2022*			*2021*
Beginning balance	$	80		$	—
Add: Accruals for warranties issued during the period		42			80
Less: Adjustment for inventory at cost and excessive and obsolete inventory		(72	)		—
Ending balance	$	50		$	80

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]

	*Year Ended December 31,*
	*2022*		*2021*		*2020*
Common stock warrants		7,303,832		—		612,310
Common stock options		5,250,696		5,996,813		5,039,194
Restricted stock units		—		—		111,305
Total		12,554,528		5,996,813		5,762,809

Note 6 - Stockholders' Equity and Stock-based Compensation - Summary of Performance Option Activity (Details) - Performance Options [Member] - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Options balances, number of shares (in shares)	1,200,097
Options balances, weighted average exercise price (in dollars per share)	$ 13.11
Options balances, weighted average remaining life (Year)	7 years 7 days	8 years 5 months 8 days
Options granted, number of shares (in shares)	200,000
Options granted, weighted average exercise price (in dollars per share)	$ 5.32
Options exercised, number of shares (in shares)	0
Options exercised, weighted average exercise price (in dollars per share)	$ 0
Options canceled, number of shares (in shares)	(797,920)
Options canceled, weighted average exercise price (in dollars per share)	$ 13.32
Options expired, number of shares (in shares)	(81,875)
Options expired, weighted average exercise price (in dollars per share)	$ 11.28
Options balances, number of shares (in shares)	520,302	1,200,097
Options balances, weighted average exercise price (in dollars per share)	$ 10.08	$ 13.11
Options exercisable, number of shares (in shares)	248,861
Options exercisable, weighted average exercise price (in dollars per share)	$ 12.25
Options exercisable, weighted average remaining life (Year)	4 years 11 months 1 day

Note 10 - Segment Reporting - Revenue by Product (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Total revenues	$ 700	$ 1,418	$ 0
System Products [Member]
Total revenues	560	1,189	0
Cycle Units Products [Member]
Total revenues	$ 140	$ 229	$ 0

Note 7 - Research Grants and Agreements (Details Textual) - USD ($) $ in Thousands	1 Months Ended				12 Months Ended
	May 31, 2021	Mar. 31, 2021	Sep. 30, 2019	Aug. 31, 2018	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Research and Development Expense, Total					$ 20,839	$ 28,640	$ 26,444
Old Dominion University Research Foundation [Member] \| Sponsored Research Agreement SRA [Member]
Research and Development Expense, Total					$ 200	$ 300	$ 600
Old Dominion University Research Foundation [Member] \| Sponsored Research Agreement SRA [Member] \| Research and Development Arrangement [Member]
Long-Term Purchase Commitment, Amount	$ 300	$ 300	$ 800	$ 800

Note 5 - Goodwill (Details Textual) $ in Thousands	12 Months Ended
Note 5 - Goodwill (Details Textual) $ in Thousands	Dec. 31, 2022 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2021 USD ($)
Goodwill, Ending Balance	$ 2,791		$ 2,791
Goodwill, Impairment Loss	$ 0
Series of Individually Immaterial Business Acquisitions [Member]
Number of Businesses Acquired		3
Business Combination, Consideration Transferred, Total		$ 5,500
Goodwill, Ending Balance		$ 2,800