0001437749-24-015092 | 10-Q | XBRL Viewer

Commitments and Contingencies Disclosure [Text Block]

8. Commitments and Contingencies

2022 Loan Agreement

On September 20, 2022, the Company and Robert W. Duggan, the Company's majority stockholder and 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 2022 Loan Agreement bore 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 amended certain terms of the 2022 Loan Agreement. There were no changes to the interest rate, but the principal sum repayment date was changed to September 30, 2024. During the year ended December 31, 2023, the Company made cash payments of $1.7 million for accrued interest on the loan, and recorded an additional $1.1 million of interest expense in relation to the 2022 Loan Agreement. On April 30, 2023, the Company entered into a Securities Purchase Agreement with Mr. Duggan, pursuant to which the Company agreed to issue and sell to Mr. Duggan 10,022,937 shares of the Company’s common stock, par value $0.001 per share, in a Private Placement, at a price per share of $6.51. These shares were paid for through the cancellation of the amounts then owed by the Company under the 2022 Loan Agreement, the principal sum of $65.0 million and all accrued and unpaid interest outstanding, which totaled approximately $0.2 million as of April 30, 2023. The parties completed the Private Placement on May 9, 2023 and, upon closing and satisfaction of the outstanding debt, the 2022 Loan Agreement terminated, without early termination fees or penalties being owed by the Company. No additional amounts are owed to Mr. Duggan under the 2022 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 in 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.

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

	*March 31,*		*December 31,*
Assets:	*2024*		*2023*
Right-of-use assets	$	7,040	$	7,256

	*March 31,*		*December 31,*
Liabilities:	*2024*		*2023*
Current operating lease liabilities	$	1,101	$	1,058
Non-current operating lease liabilities		7,796		8,086
Total lease liabilities	$	8,897	$	9,144

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

	*Three Months Ended March 31,*
	*2024*		*2023*
Cash paid for operating lease liabilities	$	469	$	453

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

Year ending December 31:
2024 (remaining 9 months)	$	1,441
2025		1,977
2026		2,046
2027		2,117
Thereafter		4,074
Total lease payments		11,655
Less imputed interest		(2,758	)
Total lease liabilities	$	8,897

Weighted-average remaining lease term and discount rate, as of March 31, 2024, were as follows:

Weighted-average remaining lease term			5.59
Weighted-average discount rate			10	%

Rent expense, including common area maintenance charges, was approximately $0.6 million and $0.5 million for the three-month periods ended March 31, 2024 and 2023, respectively.

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 is not able to conclude that a liability is probable and cannot predict what the final outcome of Ms. Gardiner’s arbitration proceeding will likely be or provide a reasonable estimate for the range of ultimate possible loss, if any. However, at this time, we believe that the final resolution of this matter will not adversely affect our consolidated position, results of operations, or cash flows and that a liability is not probable at this time.

Note 6 - Stockholders' Equity and Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended				3 Months Ended		6 Months Ended	12 Months Ended
	Apr. 30, 2023	Jan. 01, 2023	Jun. 09, 2022	Mar. 31, 2024	Dec. 31, 2023	May 31, 2021	Nov. 30, 2017	Mar. 31, 2024	Mar. 31, 2023	Jun. 15, 2023	Dec. 31, 2023	Dec. 31, 2017	Sep. 30, 2023
Common Stock, Par or Stated Value Per Share (in dollars per share)				$ 0.001	$ 0.001			$ 0.001			$ 0.001
Proceeds from Warrant Exercises								$ 0	$ 194
Time-based Options [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Intrinsic Value								$ 3,500
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								$ 300
Market-based Options [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Intrinsic Value								$ 700
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
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares)		1,200,000			1,375,000
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Number of Shares (in shares)												1,200,000
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Percent												4.00%
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)				810,758				810,758
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)				2,000,000		1,000,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)				3,249,126				3,249,126
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 Inducement Equity Incentive Plan [Member] \| Share-Based Payment Arrangement, Option [Member] \| Maximum [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)							10 years
The 2017 Employee Stock Purchase Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)												250,000
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Number of Shares (in shares)				450,000				450,000				450,000
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Percent												1.50%
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)				485,359				485,359
Stock Issued During Period, Shares, Employee Stock Purchase Plans (in shares)								77,959
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, Exercise Price of Warrants or Rights (in dollars per share)			$ 2.05		$ 2.05						$ 2.05
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)					7,317,072						7,317,072
Class of Warrants or Rights, Redemption Price Per Share (in dollars per share)					$ 0.01						$ 0.01
Class of Warrant or Right, Period of Written Notice for Exercise (Day)											30 days
Class of Warrant or Right, Percentage Required for Redemption					200.00%						200.00%
Class of Warrant or Right, Exercise, Consecutive Trading Days (Day)											20 days
Class of Warrant or Right, Exercised During Period (in shares)										7,250,897	66,175
Proceeds from Warrant Exercises										$ 14,900
Class of Warrant or Right, Outstanding (in shares)													0
Loan Agreement [Member]
Debt Instrument, Decrease, Forgiveness	$ 65,000
Private Placement [Member] \| Robert W. Duggan [Member]
Stock Issued During Period, Shares, New Issues (in shares)	10,022,937
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.001
Shares Issued, Price Per Share (in dollars per share)	$ 6.51
Rights Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)			7,317,072
Common Stock, Par or Stated Value Per Share (in dollars per share)			$ 0.001
Shares Issued, Price Per Share (in dollars per share)			$ 2.05
Equity Offering, Units, Sale of Units (in shares)			7,317,072
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 Warrants or Rights (in shares)			7,317,072
Proceeds from Issuance of Common Stock			$ 15,000
Class of Warrants or Rights, Redemption Price Per Share (in dollars per share)			$ 0.01
Rights Offering [Member] \| Board of Directors Chairman [Member]
Investment Owned, Percent of Net Assets			56.00%

Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2024

Accounting Policies [Abstract]

Going Concern [Policy Text Block]

Going Concern

As of March 31, 2024, the Company had an accumulated deficit of $347.1 million, cash outflows from operations of $9.8 million for the three months then ended, cash and cash equivalents of $34.9 million and a net loss of $10.1 million. The Company anticipates net losses for the next several years or until it can generate substantial product revenue and achieve profitability. Based on the Company’s current operating plan, the Company has determined that, with its current financial resources, the Company would be able to operate into the first quarter of 2025. As the Company’s operating plan does not allow the Company to operate for a period of twelve months from the date the condensed consolidated financial statements are issued without additional financing, based on the Accounting Standards Codification (“ASC”) 205-40, Presentation of Financial Statements – Going Concern, the Company is required to disclose that substantial doubt regarding the Company’s ability to continue as a going concern exists. This evaluation initially cannot take into consideration the potential mitigating effects of plans that have not been fully implemented as of the date the financial statements are issued. To continue to fund the operations of the Company beyond this time period, management has developed a plan, which primarily consists of raising additional capital through a rights offering expected to close in the second quarter of 2024. Additionally, the Company may utilize some combination of public or private equity offerings, debt financings, or potential new collaborations in the future. There is no assurance, however, that any additional financing or any revenue-generating collaboration will be available when needed or that management of the Company will be able to obtain financing or enter into a collaboration on terms acceptable to the Company. The accompanying consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The consolidated financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of this uncertainty.

Basis of Accounting, Policy [Policy Text Block]

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements have been prepared on a basis consistent with the Company’s December 31, 2023 audited Consolidated Financial Statements and include all adjustments, consisting of only normal recurring adjustments, necessary to fairly state the information set forth herein. The condensed consolidated financial statements have been prepared in accordance with the applicable rules and regulations of the Securities and Exchange Commission (the “SEC”) and, as permitted by such rules and regulations, omit certain information and footnote disclosures necessary to present the financial statements in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”). The condensed consolidated balance sheet as of December 31, 2023 was derived from the audited consolidated financial statements as of that date but does not include all of the information and footnotes required by U.S. GAAP for complete financial statements. These condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023. The results of operations for the three-month period ended March 31, 2024, are not necessarily indicative of the results to be expected for the entire year or any future periods.

Consolidation, Policy [Policy Text Block]

Principles of Consolidation

The accompanying condensed consolidated financial statements include the financial statements of Pulse Biosciences, Inc. and its wholly-owned subsidiaries. Intercompany balances and transactions, if any, 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 stock-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.

Share-Based Payment Arrangement [Policy Text Block]

Stock-Based Compensation

The Company's stock-based compensation programs include stock options and an employee stock purchase program.

The Company periodically issues stock options to officers, directors, employees, and consultants for services rendered. Such issuances vest and expire according to terms established at the issuance date. Stock-based payments to officers, directors and employees, including grants of employee stock options, are recognized in the financial statements based on their grant date fair values, which are estimated using the Black-Scholes option-pricing model. Stock-based compensation expense is charged to operations on a straight-line basis over the vesting period. The Company has granted stock options with both time-based as well as performance-based vesting conditions. For stock awards with performance-based vesting conditions, the Company does not recognize compensation expense until it is probable that the performance-based vesting condition will be achieved. The analysis to determine such probability involves estimates and judgements from management and the estimate of expense may be revised periodically.

The Company has also issued certain stock options with market-based vesting conditions. These vesting conditions relate to the achievement of certain market capitalization targets of the Company. The grant date fair value for these stock options was determined using a Monte Carlo simulation. The expense is recognized over the requisite service period for each tranche of the awards. The requisite service period is the service period derived from the Monte Carlo simulation model. If the market capitalization targets are met sooner than the derived service period, the Company will accelerate the recognition of stock-based compensation expense to reflect the cumulative expense associated with the vested shares. The Monte Carlo simulation requires the Company to make assumptions and judgements about the variables used in the calculation including the expected term, volatility of the Company's common stock, an assumed risk-free interest rate, and cost of equity. The assumptions used in the option-pricing model represent management’s best estimates. If factors change and different assumptions are used, the Company's stock-based compensation expense could be materially different in the future.

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

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 accrued 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. In June 2023, the Company reduced the accrued warranty liability to zero. Based upon the Company's shift in focus, there are a limited number of consoles currently covered under the standard warranty. All inventory has been fully written off, therefore the only incremental costs to fulfill a warranty claim in 2024 would be shipping costs or the costs to replace the CellFX nsPFA electrode, which would be immaterial in nature.

Warranty accrual activity consisted of the following for the three-month periods ended March 31, 2024 and 2023 (in thousands):

	*Three Months Ended March 31,*
	*2024*		*2023*
Beginning balance	$	—	$	50
Add: Accruals for warranties issued during the period		—		—
Less: Adjustment for inventory at cost and excessive and obsolete inventory		—		—
Ending balance	$	—	$	50

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.

Basic and diluted net loss per common share is the same for all periods presented because all warrants, stock options and restricted stock units outstanding are anti-dilutive.

The following outstanding stock options, and warrants 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:

	*Three Months Ended March 31,*
	*2024*		*2023*
Common stock warrants		—		7,208,193
Common stock options		10,096,411		5,608,210
Total		10,096,411		12,816,403

New Accounting Pronouncements, Policy [Policy Text Block]

Recent Accounting Pronouncements Not Yet Adopted

As of March 31, 2024, there were no material changes to the information provided regarding recent accounting pronouncements in Note 2, “Summary of Significant Accounting Policies” in the Company’s Form 10-K for the fiscal year ended December 31, 2023.

Disclosure of accounting policy for award under share-based payment arrangement. Includes, but is not limited to, methodology and assumption used in measuring cost.

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Note 3 - Fair Value of Financial Instruments (Details Textual) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Impairment of Marketable Securities	$ 0	$ 0

Note 6 - Stockholders' Equity and Stock-based Compensation - Summary of Market-based Option Activity (Details) - Market-based Options [Member] - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Options balances, number of shares (in shares)	2,100,000
Options balances, weighted average exercise price (in dollars per share)	$ 6.78
Options balances, weighted average remaining life (Year)	9 years 2 months 19 days	9 years 5 months 8 days
Options granted, number of shares (in shares)	100,000
Options granted, weighted average exercise price (in dollars per share)	$ 9.32
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)	0
Options canceled, weighted average exercise price (in dollars per share)	$ 0
Options expired, number of shares (in shares)	0
Options expired, weighted average exercise price (in dollars per share)	$ 0
Options balances, number of shares (in shares)	2,200,000	2,100,000
Options balances, weighted average exercise price (in dollars per share)	$ 6.89	$ 6.78
Options exercisable, number of shares (in shares)	0
Options exercisable, weighted average exercise price (in dollars per share)	$ 0

Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - $ / shares shares in Thousands	Mar. 31, 2024	Dec. 31, 2023
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	50,000	50,000
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	500,000
Common stock, shares issued (in shares)	55,225	55,144
Common stock, shares outstanding (in shares)	55,225	55,144

Note 8 - Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2024

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

	*March 31,*		*December 31,*
Assets:	*2024*		*2023*
Right-of-use assets	$	7,040	$	7,256

	*March 31,*		*December 31,*
Liabilities:	*2024*		*2023*
Current operating lease liabilities	$	1,101	$	1,058
Non-current operating lease liabilities		7,796		8,086
Total lease liabilities	$	8,897	$	9,144

	*Three Months Ended March 31,*
	*2024*		*2023*
Cash paid for operating lease liabilities	$	469	$	453

Year ending December 31:
2024 (remaining 9 months)	$	1,441
2025		1,977
2026		2,046
2027		2,117
Thereafter		4,074
Total lease payments		11,655
Less imputed interest		(2,758	)
Total lease liabilities	$	8,897

Weighted-average remaining lease term			5.59
Weighted-average discount rate			10	%

Note 6 - Stockholders' Equity and Stock-based Compensation

3 Months Ended

Mar. 31, 2024

Share-Based Payment Arrangement [Text Block]

6. Stockholders’ Equity and Stock-Based Compensation

Private Placement Securities Purchase Agreement

On April 30, 2023, the Company entered into a Securities Purchase Agreement with Robert W. Duggan, the Company’s majority stockholder and Executive Chairman, pursuant to which the Company agreed to issue and sell to Mr. Duggan 10,022,937 shares of the Company’s common stock, par value $0.001 per share, in a Private Placement, at a price per share of $6.51. The parties completed the Private Placement on May 9, 2023, after satisfying all pre-closing conditions, and the Company issued the full number of shares to Mr. Duggan. The shares were paid for through the cancellation of the principal sum of $65.0 million borrowed by the Company pursuant to the 2022 Loan Agreement (See Note 8), together with all accrued and unpaid interest outstanding owed at the time of closing.

Rights Offerings

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 at a price of $2.05 per share. 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. In May 2023, the Company delivered an irrevocable notice of redemption to warrant holders and, on June 16, 2023, it redeemed the last of the outstanding 2022 Rights Offering Warrants at a price of $0.01 per warrant share. See the Common Stock Warrants section below for further details. Robert W. Duggan, the Company’s majority stockholder and Executive Chairman, purchased approximately 56% of the shares offered through the 2022 Rights Offering.

Common Stock Warrants

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 were 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. On May 10, 2023, the Company issued a press release announcing that on May 9, 2023 the terms for warrant redemption had been met. Pursuant to the redemption, the Company redeemed 66,175 warrants on the redemption date, June 16, 2023. Prior to the redemption date, warrants to purchase 7,250,897 shares were exercised, generating approximately $14.9 million of total gross proceeds to the Company. As of September 30, 2023, there were no 2022 Rights Offering Warrants outstanding.

Equity Plans

2017 Equity Incentive Plan and 2017 Inducement Equity Incentive Plan

The Board of Directors of the Company (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 at both January 1, 2024 and 2023, the number of shares of common stock available under the 2017 Plan increased by 1,200,000, 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. Additionally, in December 2023, the number of shares of common stock available under the 2017 Plan increased by 1,375,000 shares as a result of a stockholder vote held at a special meeting of stockholders. As of March 31, 2024, 810,758 shares of common stock remained available for issuance under the 2017 Plan.

During November 2017, the Board 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. And, in March 2024, the Board approved a second amendment to the Inducement Plan to reserve an additional 2,000,000 shares of the Company’s common stock for issuance pursuant to the Inducement Plan. As of March 31, 2024, 3,249,126 shares of common stock remained available for issuance under the Inducement Plan.

A summary of stock option activity under the 2015 Plan, 2017 Plan and Inducement Plan for the three-months ended March 31, 2024 is presented below:

	*Stock Options Outstanding*
	*Number of shares*			*Weighted average exercise price*		*Weighted average remaining life (in years)*
Balances — December 31, 2023		9,466,036		$	9.01		7.78
Options granted		639,000			9.00
Options exercised		(3,000	)		2.92
Options canceled		(4,125	)		6.65
Options expired		(1,500	)		17.01
Balances — March 31, 2024		10,096,411		$	9.01		7.69
Exercisable — March 31, 2024		4,021,494		$	13.58		5.41

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 three-months ended March 31, 2024 is presented below:

	*Stock Options Outstanding*
	*Number of shares*			*Weighted average exercise price*		*Weighted average remaining life (in years)*
Balances — December 31, 2023		6,141,906		$	10.48		7.07
Options granted		500,000			8.98
Options exercised		—			—
Options canceled		(1,125	)		16.60
Options expired		(1,500	)		17.01
Balances — March 31, 2024		6,639,281		$	10.36		7.05
Exercisable — March 31, 2024		3,580,866		$	14.31		5.15

The fair value of the time-based options granted during the three-month period ended March 31, 2024 was $3.5 million.

Performance-based Options

Certain stock options awarded by the Company contain performance conditions related to certain financial measures and achievements of strategic and operational milestones. Once a specific performance condition is fulfilled, the associated options will fully vest and become exercisable.

A summary of the performance-based option activity under the 2017 Plan and Inducement Plan for the three-months ended March 31, 2024 is presented below:

	*Stock Options Outstanding*
	*Number of shares*			*Weighted average exercise price*		*Weighted average remaining life (in years)*
Balances — December 31, 2023		1,224,130		$	5.51		8.53
Options granted		39,000			8.44
Options exercised		(3,000	)		2.92
Options canceled		(3,000	)		2.92
Options expired		—			—
Balances — March 31, 2024		1,257,130		$	5.61		8.35
Exercisable — March 31, 2024		440,628		$	7.60		7.5

The fair value of the performance-based options granted during the three-month period ended March 31, 2024 was $0.3 million.

Market-based Options

Certain stock options awarded by the Company contain market conditions related to achievement of certain market capitalization targets. The options will vest and become exercisable once the specific market capitalization targets are fulfilled.

A summary of the market-based option activity under the 2017 Plan for the three-months ended March 31, 2024 is presented below:

	*Stock Options Outstanding*
	*Number of shares*		*Weighted average exercise price*		*Weighted average remaining life (in years)*
Balances — December 31, 2023		2,100,000	$	6.78		9.44
Options granted		100,000		9.32
Options exercised		—		—
Options canceled		—		—
Options expired		—		—
Balances — March 31, 2024		2,200,000	$	6.89		9.22
Exercisable — March 31, 2024		—		—		—

The fair value of the market-based options granted during the three-month period ended March 31, 2024 was $0.7 million.

The Company estimates the fair value of time-based and performance-based stock options on the grant date using the Black-Scholes option pricing model. The estimated fair value of these employee stock options is amortized on a straight-line basis over the requisite service period of the awards. The Company reviews, and when deemed appropriate, updates the assumptions used on a periodic basis. The fair value of time-based and performance-based stock options was estimated using the following weighted-average assumptions:

	*Three Months Ended March 31,*
	*2024*		*2023*
Expected term in years		5.3 - 6.3		6.03
Expected volatility		91% - 95%		94%
Risk-free interest rate		4.0% - 4.5%		3.8%
Dividend yield		—		—

The Company estimates the fair value of market-based stock options on the grant date using a Monte Carlo simulation model. The estimated fair value of these employee stock options is amortized over the requisite service period for each tranche of the awards. The requisite service period is the service period derived from the Monte Carlo simulation model. If the market capitalization targets are met sooner than the derived service period, the Company will accelerate the recognition of stock-based compensation expense to reflect the cumulative expense associated with the vested shares. The fair value of market-based stock options was estimated using the following weighted-average assumptions:

	*Three Months Ended March 31,*
	*2024*		*2023*
Expected term in years		5.5 - 5.8		—
Expected volatility		90%		—
Risk-free interest rate		4.2%		—
Dividend yield		—		—

2017 Employee Stock Purchase Plan

The Board previously adopted, and the Company's 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 2024, the Company reserved an additional 450,000 shares under the 2017 ESPP pursuant to the evergreen provision. In 2023, the Board waived the evergreen provision and no additional shares were reserved under the 2017 ESPP. During the three months ended March 31, 2024, the Company issued 77,959 shares of common stock under the 2017 ESPP. As of March 31, 2024, 485,359 shares of common stock remained available for issuance under the 2017 ESPP.

The Company estimates the fair value of ESPP grants on their grant date using the Black-Scholes option pricing model. The estimated fair value of ESPP grants is amortized on a straight-line basis over the requisite service period of the grants. The Company reviews, and when deemed appropriate, updates the assumptions used on a periodic basis. The Company utilizes its estimated volatility in the Black-Scholes option pricing model to determine the fair value of ESPP grants. The fair value of ESPP grants was estimated using the following weighted-average assumptions:

	*Three Months Ended March 31,*
	*2024*		*2023*
Expected term in years		0.5 - 1.0		0.5 - 1.0
Expected volatility		98%		83%
Risk-free interest rate		4.9% - 5.3%		5.1% - 5.2%
Dividend yield		—		—

Stock-based Compensation

Total stock-based compensation expense consisted of the following (in thousands):

	*Three Months Ended March 31,*
	*2024*		*2023*
Research and development		949		258
General and administrative		810		638
Total stock-based compensation expense	$	1,759	$	896

As of March 31, 2024, 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.

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

	*Three Months Ended March 31,*
	*2024*		*2023*
Time-based options	$	1,163	$	678
Performance-based options		8		117
Market-based options		507		—
ESPP		81		101
Total stock-based compensation expense	$	1,759	$	896

Note 3 - Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2024

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

		*March 31, 2024*
Assets	*Classification*	*Level 1*		*Level 2*		*Level 3*		*Total*
Money market funds	Cash and cash equivalents	$	32,702	$	—	$	—	$	32,702
Total assets measured at fair value		$	32,702	$	—	$	—	$	32,702

		*December 31, 2023*
Assets	*Classification*	*Level 1*		*Level 2*		*Level 3*		*Total*
Money market funds	Cash and cash equivalents	$	41,184	$	—	$	—	$	41,184
Total assets measured at fair value		$	41,184	$	—	$	—	$	41,184

Note 4 - Balance Sheet Components (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Depreciation	$ 132	$ 135
Finite-Lived Intangible Asset, Useful Life (Year)	12 years

Note 4 - Balance Sheet Components

3 Months Ended

Mar. 31, 2024

Supplemental Balance Sheet Disclosures [Text Block]

4. Balance Sheet Components

Property and Equipment, Net

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

	*March 31,*			*December 31,*
	*2024*			*2023*
Leasehold improvements	$	2,519		$	2,519
Laboratory equipment		1,247			1,247
Furniture, fixtures and equipment		966			966
Software		272			272
Construction in progress		5			—
Total property and equipment		5,009			5,004
Less: Accumulated depreciation and amortization		(3,609	)		(3,476	)
Total property and equipment, net	$	1,400		$	1,528

Depreciation expense was $0.1 million for each of the three-month periods ended March 31, 2024 and 2023.

Intangible Assets, Net

Intangible assets primarily consist of acquired licenses to utilize certain patents, know-how and technology relating to the Company’s NPS technology for biomedical applications acquired from Old Dominion University Research Foundation (“ODURF”), Eastern Virginia Medical School, and the University of Southern California. In addition, the Company entered into a Sponsored Research Agreement with Old Dominion University’s Frank Reidy Research Center for Bioelectrics, 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):

	*March 31,*			*December 31,*
	*2024*			*2023*
Acquired patents and licenses	$	7,985		$	7,985
Less: Accumulated amortization		(6,266	)		(6,099	)
Total intangible assets, net	$	1,719		$	1,886

A schedule of the amortization of intangible assets for the remainder of 2024 and the succeeding two fiscal years is as follows (in thousands):

Years ending December 31:
2024 (remaining 9 months)	$	498
2025		665
2026		556
Total	$	1,719

Accrued Expenses

Accrued expenses consisted of the following (in thousands):

	*March 31,*		*December 31,*
	*2024*		*2023*
Compensation expense	$	1,783	$	3,199
Clinical trial fees and costs		56		84
Professional fees		232		343
Other		197		188
Total accrued expenses	$	2,268	$	3,814

Note 1 - Description of the Business

3 Months Ended

Mar. 31, 2024

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 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, or end-effectors, 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 primary efforts on the use of nsPFA energy and the CellFX platform in the treatment of atrial fibrillation ("AF") and in a select few other markets where it could have a profound positive impact on healthcare for both patients and providers.

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 maintains a website at www.pulsebiosciences.com where general information about the Company is available.

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 had minimal revenue and currently generates no 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 4 - Balance Sheet Components - Intangible Assets, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Less: Accumulated amortization	$ (6,266)	$ (6,099)
Total	1,719	1,886
Acquired Patents and Licenses [Member]
Acquired patents and licenses	$ 7,985	$ 7,985

Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 34,885	$ 44,365
Prepaid expenses and other current assets	964	963
Total current assets	35,849	45,328
Property and equipment, net	1,400	1,528
Intangible assets, net	1,719	1,886
Goodwill	2,791	2,791
Right-of-use assets	7,040	7,256
Other assets	365	365
Total assets	49,164	59,154
Current liabilities:
Accounts payable	1,712	1,836
Accrued expenses	2,268	3,814
Lease liability, current	1,101	1,058
Total current liabilities	5,081	6,708
Lease liability, less current portion	7,796	8,086
Total liabilities	12,877	14,794
Commitments and contingencies (Note 8)
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 – 55,225 shares and 55,144 shares at March 31, 2024 and December 31, 2023 respectively	55	55
Additional paid-in capital	383,284	381,220
Accumulated other comprehensive income (loss)	0	0
Accumulated deficit	(347,052)	(336,915)
Total stockholders’ equity	36,287	44,360
Total liabilities and stockholders’ equity	$ 49,164	$ 59,154

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Revenues:
Total revenues	$ 0	$ 0
Cost and expenses:
Research and development	6,741	5,829
General and administrative	3,874	3,733
Total cost and expenses	10,615	9,562
Loss from operations	(10,615)	(9,562)
Other income (expense):
Interest income (expense), net	478	(239)
Total other income (expense)	478	(239)
Loss from operations, before income taxes	(10,137)	(9,801)
Income tax benefit	0	0
Net loss	(10,137)	(9,801)
Comprehensive loss	$ (10,137)	$ (9,801)
Net loss per share:
Basic and diluted net loss per share (in dollars per share)	$ (0.18)	$ (0.26)
Weighted average shares used to compute net loss per common share — basic and diluted (in shares)	55,172	37,390

Note 12 - Subsequent Events (Details Textual) - USD ($) $ / shares in Units, $ in Millions	May 16, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 09, 2022
Common Stock, Par or Stated Value Per Share (in dollars per share)		$ 0.001	$ 0.001
Rights Offering Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)				1
Subsequent Event [Member] \| Rights Offering Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)	0.5
Class of Warrans or Right, Exercise Price, Percentage of Subscription Price for Units	110.00%
Rights Offering [Member]
Common Stock, Par or Stated Value Per Share (in dollars per share)				$ 0.001
Number of Shares Per Unit Issued (in shares)				1
Rights Offering [Member] \| Subsequent Event [Member]
Equity Offering, Units, Maximum Amount Authorized	$ 60
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01
Number of Shares Per Unit Issued (in shares)	1
Number of Warrants in Each Unit (in shares)	2
Subscription Price Per Unit, Maximum Benchmark (in dollars per share)	$ 10

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Mar. 31, 2024
Insider Trading Arr Line Items
Material Terms of Trading Arrangement [Text Block]	Item 5. Other Information Trading Arrangements During the three-month period ended March 31, 2024, none of our directors or officers (as defined in Rule 16a-1(f) under the Exchange Act) adopted or terminated a “Rule 10b5-1 trading arrangement” or a “non-Rule 10b5-1 trading arrangement” as such terms are defined under Item 408 of Regulation S-K.
Rule 10b5-1 Arrangement Adopted [Flag]	false
Non-Rule 10b5-1 Arrangement Adopted [Flag]	false
Rule 10b5-1 Arrangement Terminated [Flag]	false
Non-Rule 10b5-1 Arrangement Terminated [Flag]	false

Note 3 - Fair Value of Financial Instruments

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Text Block]

3. Fair Value of Financial Instruments

The authoritative guidance with respect to fair value established a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three levels, and requires that assets and liabilities carried at fair value be classified and disclosed in one of three categories, as presented below.

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. The Company did not classify any of its investments within Level 2 of the fair value hierarchy.

Level 3 - Unobservable inputs for 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 as of March 31, 2024 and December 31, 2023, respectively (in thousands):

		*March 31, 2024*
Assets	*Classification*	*Level 1*		*Level 2*		*Level 3*		*Total*
Money market funds	Cash and cash equivalents	$	32,702	$	—	$	—	$	32,702
Total assets measured at fair value		$	32,702	$	—	$	—	$	32,702

		*December 31, 2023*
Assets	*Classification*	*Level 1*		*Level 2*		*Level 3*		*Total*
Money market funds	Cash and cash equivalents	$	41,184	$	—	$	—	$	41,184
Total assets measured at fair value		$	41,184	$	—	$	—	$	41,184

The Company did not have any financial liabilities measured on a recurring basis as of March 31, 2024 or December 31, 2023.

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.

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Note 2 - Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Antidilutive securities (in shares)	10,096,411	12,816,403
Warrant [Member]
Antidilutive securities (in shares)	0	7,208,193
Share-Based Payment Arrangement, Option [Member]
Antidilutive securities (in shares)	10,096,411	5,608,210

Note 12 - Subsequent Events

3 Months Ended

Mar. 31, 2024

Subsequent Events [Text Block]

12. Subsequent Events

As approved by the Company’s Board, a rights offering of up to $60 million worth of units (“Units”) will likely be available to all holders of record of the Company’s common stock, par value $0.01 (the “Common Stock”), as of the close of the market on a record date expected to be set by the Board in mid- June 2024 (the “Proposed Rights Offering”). Each Unit will likely consist of one share of Common Stock and two warrants, each to purchase one-half of one share of Common Stock, with each warrant having different redemption provisions. The subscription price per Unit is expected to equal to the lesser of (i) $10.00 per Unit and (ii) the volume weighted average price of the Company’s Common Stock for the ten trading day period through and including the expiration date of the offering, which has not yet been set by the Board. The subscription price would determine the final number of Units issuable, and subsequently the pro rata number of Units to which stockholders can subscribe. Each warrant will likely have a per share exercise price equal to 110% of the subscription price for the Units. The Company intends to distribute to all holders of Common Stock as of the record date non-transferable subscription rights to purchase Units at the price provided above.

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	Mar. 31, 2024	Dec. 31, 2023
Options balances, number of shares (in shares)	9,466,036
Options balances, weighted average exercise price (in dollars per share)	$ 9.01
Options balances, weighted average remaining life (Year)	7 years 8 months 8 days	7 years 9 months 10 days
Options granted, number of shares (in shares)	639,000
Options granted, weighted average exercise price (in dollars per share)	$ 9
Options exercised, number of shares (in shares)	(3,000)
Options exercised, weighted average exercise price (in dollars per share)	$ 2.92
Options canceled, number of shares (in shares)	(4,125)
Options canceled, weighted average exercise price (in dollars per share)	$ 6.65
Options expired, number of shares (in shares)	(1,500)
Options expired, weighted average exercise price (in dollars per share)	$ 17.01
Options balances, number of shares (in shares)	10,096,411	9,466,036
Options balances, weighted average exercise price (in dollars per share)	$ 9.01	$ 9.01
Options exercisable, number of shares (in shares)	4,021,494
Options exercisable, weighted average exercise price (in dollars per share)	$ 13.58
Options exercisable, weighted average remaining life (Year)	5 years 4 months 28 days

Note 8 - Commitments and Contingencies - Information Related to Right-of-use Assets and Lease Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Right-of-use assets	$ 7,040		$ 7,256
Current operating lease liabilities	1,101		1,058
Non-current operating lease liabilities	7,796		8,086
Total lease liabilities	8,897		$ 9,144
Cash paid for operating lease liabilities	469	$ 453
2024 (remaining 9 months)	1,441
2025	1,977
2026	2,046
2027	2,117
Thereafter	4,074
Total lease payments	11,655
Less imputed interest	$ (2,758)
Weighted-average remaining lease term (Year)	5 years 7 months 2 days
Weighted-average discount rate	10.00%

Note 6 - Stockholders' Equity and Stock-based Compensation - Summary of Time-based Option Activity (Details) - Time-based Options [Member] - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Options balances, number of shares (in shares)	6,141,906
Options balances, weighted average exercise price (in dollars per share)	$ 10.48
Options balances, weighted average remaining life (Year)	7 years 18 days	7 years 25 days
Options granted, number of shares (in shares)	500,000
Options granted, weighted average exercise price (in dollars per share)	$ 8.98
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)	(1,125)
Options canceled, weighted average exercise price (in dollars per share)	$ 16.6
Options expired, number of shares (in shares)	(1,500)
Options expired, weighted average exercise price (in dollars per share)	$ 17.01
Options balances, number of shares (in shares)	6,639,281	6,141,906
Options balances, weighted average exercise price (in dollars per share)	$ 10.36	$ 10.48
Options exercisable, number of shares (in shares)	3,580,866
Options exercisable, weighted average exercise price (in dollars per share)	$ 14.31
Options exercisable, weighted average remaining life (Year)	5 years 1 month 24 days

Note 4 - Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Property and equipment, gross	$ 5,009	$ 5,004
Less: Accumulated depreciation and amortization	(3,609)	(3,476)
Total property and equipment, net	1,400	1,528
Leasehold Improvements [Member]
Property and equipment, gross	2,519	2,519
Laboratory Equipment [Member]
Property and equipment, gross	1,247	1,247
Furniture and Fixtures [Member]
Property and equipment, gross	966	966
Software and Software Development Costs [Member]
Property and equipment, gross	272	272
Construction in Progress [Member]
Property and equipment, gross	$ 5	$ 0

Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Retained Earnings (Accumulated Deficit)	$ (347,052)		$ (336,915)
Net Cash Provided by (Used in) Operating Activities	(9,780)	$ (6,570)
Cash and Cash Equivalents, at Carrying Value	34,885		$ 44,365
Net Income (Loss) Attributable to Parent	$ (10,137)	$ (9,801)

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount of accumulated undistributed earnings (deficit).

+ References + Details

Note 8 - Commitments and Contingencies (Details Textual) $ / shares in Units, $ in Millions		3 Months Ended		12 Months Ended
	Apr. 30, 2023 USD ($) $ / shares shares	Mar. 31, 2024 USD ($) $ / shares	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) $ / shares	Sep. 20, 2022 USD ($)	May 31, 2019 a	Jul. 31, 2017 a
Common Stock, Par or Stated Value Per Share (in dollars per share) \| $ / shares		$ 0.001		$ 0.001
Operating Lease, Expense		$ 0.6	$ 0.5
Corporate Headquarters in Hayward, California [Member]
Lessee, Operating Lease, Term of Contract (Year)							5 years
Area of Real Estate Property (Acre) \| a							15,700
Corporate Headquarters in Hayward, California [Member] \| Expansion Premises 1 [Member]
Area of Real Estate Property (Acre) \| a						13,300
Corporate Headquarters in Hayward, California [Member] \| Expansion Premises 2 [Member]
Area of Real Estate Property (Acre) \| a						21,300
Robert W. Duggan [Member] \| Private Placement [Member]
Stock Issued During Period, Shares, New Issues (in shares) \| shares	10,022,937
Common Stock, Par or Stated Value Per Share (in dollars per share) \| $ / shares	$ 0.001
Shares Issued, Price Per Share (in dollars per share) \| $ / shares	$ 6.51
Two Thousand Twenty Two Loan Agreement [Member] \| Robert W. Duggan [Member]
Debt Instrument, Face Amount					$ 65.0
Debt Instrument Quarterly Interest Rate					5
Debt Instrument, Increase, Accrued Interest				$ 1.7
Interest Expense				$ 1.1
Loan Agreement [Member]
Debt Instrument, Decrease, Forgiveness	$ 65.0
Interest Payable	$ 0.2

Note 6 - Stockholders' Equity and Stock-based Compensation - Summary of Performance Option Activity (Details) - Performance Options [Member] - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Options balances, number of shares (in shares)	1,224,130
Options balances, weighted average exercise price (in dollars per share)	$ 5.51
Options balances, weighted average remaining life (Year)	8 years 4 months 6 days	8 years 6 months 10 days
Options granted, number of shares (in shares)	39,000
Options granted, weighted average exercise price (in dollars per share)	$ 8.44
Options exercised, number of shares (in shares)	(3,000)
Options exercised, weighted average exercise price (in dollars per share)	$ 2.92
Options canceled, number of shares (in shares)	(3,000)
Options canceled, weighted average exercise price (in dollars per share)	$ 2.92
Options expired, number of shares (in shares)	0
Options expired, weighted average exercise price (in dollars per share)	$ 0
Options balances, number of shares (in shares)	1,257,130	1,224,130
Options balances, weighted average exercise price (in dollars per share)	$ 5.61	$ 5.51
Options exercisable, number of shares (in shares)	440,628
Options exercisable, weighted average exercise price (in dollars per share)	$ 7.6
Options exercisable, weighted average remaining life (Year)	7 years 6 months

Note 9 - Segment Reporting

3 Months Ended

Mar. 31, 2024

Segment Reporting Disclosure [Text Block]

9. 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. All of the Company’s long-lived assets are based in the United States.

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.

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Note 4 - Balance Sheet Components - Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Compensation expense	$ 1,783	$ 3,199
Clinical trial fees and costs	56	84
Professional fees	232	343
Other	197	188
Total accrued expenses	$ 2,268	$ 3,814

Note 4 - Balance Sheet Components (Tables)

3 Months Ended

Mar. 31, 2024

Property, Plant and Equipment [Table Text Block]

	*March 31,*			*December 31,*
	*2024*			*2023*
Leasehold improvements	$	2,519		$	2,519
Laboratory equipment		1,247			1,247
Furniture, fixtures and equipment		966			966
Software		272			272
Construction in progress		5			—
Total property and equipment		5,009			5,004
Less: Accumulated depreciation and amortization		(3,609	)		(3,476	)
Total property and equipment, net	$	1,400		$	1,528

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

	*March 31,*			*December 31,*
	*2024*			*2023*
Acquired patents and licenses	$	7,985		$	7,985
Less: Accumulated amortization		(6,266	)		(6,099	)
Total intangible assets, net	$	1,719		$	1,886

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

Years ending December 31:
2024 (remaining 9 months)	$	498
2025		665
2026		556
Total	$	1,719

Schedule of Accrued Liabilities [Table Text Block]

	*March 31,*		*December 31,*
	*2024*		*2023*
Compensation expense	$	1,783	$	3,199
Clinical trial fees and costs		56		84
Professional fees		232		343
Other		197		188
Total accrued expenses	$	2,268	$	3,814

Note 6 - Stockholders' Equity and Stock-based Compensation - Option Assumptions (Details)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Time-based and Performance Options [Member]
Dividend yield	0.00%
Market-based Options [Member]
Expected volatility	90.00%	0.00%
Risk-free interest rate	4.20%	0.00%
Dividend yield	0.00%	0.00%
Minimum [Member] \| Time-based and Performance Options [Member]
Expected term in years (Year)	5 years 3 months 18 days	6 years 10 days
Expected volatility	91.00%	94.00%
Risk-free interest rate	4.00%	3.80%
Minimum [Member] \| Market-based Options [Member]
Expected term in years (Year)	5 years 6 months
Maximum [Member] \| Time-based and Performance Options [Member]
Expected term in years (Year)	6 years 3 months 18 days
Expected volatility	95.00%
Risk-free interest rate	4.50%
Maximum [Member] \| Market-based Options [Member]
Expected term in years (Year)	5 years 9 months 18 days

Note 5 - Goodwill (Details Textual) $ in Thousands	3 Months Ended	12 Months Ended
Note 5 - Goodwill (Details Textual) $ in Thousands	Mar. 31, 2024 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2023 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

Amount, after accumulated impairment loss, of asset representing future economic benefit arising from other asset acquired in business combination or from joint venture formation or both, that is not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-Section S99
-Paragraph 1
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-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

Note 2 - Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2024

Significant Accounting Policies [Text Block]

2. Summary of Significant Accounting Policies

Going Concern

Basis of Presentation

Principles of Consolidation

Use of Estimates

Significant Accounting Policies

The Company’s significant accounting policies are described in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023. The Company continually evaluates the accounting policies and estimates used in preparing the consolidated financial statements. During both the year ended December 31, 2023, and the three-month period ended March 31, 2024, the Company issued stock options to certain employees which contain market conditions related to overall market capitalization. Additionally, the Company has issued stock options to certain employees which contain performance conditions related to certain financial measures and achievements of strategic/operational milestones.

Stock-Based Compensation

The Company's stock-based compensation programs include stock options and an employee stock purchase program.

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

Product Warranty

Warranty accrual activity consisted of the following for the three-month periods ended March 31, 2024 and 2023 (in thousands):

	*Three Months Ended March 31,*
	*2024*		*2023*
Beginning balance	$	—	$	50
Add: Accruals for warranties issued during the period		—		—
Less: Adjustment for inventory at cost and excessive and obsolete inventory		—		—
Ending balance	$	—	$	50

Net Loss per Share

Basic and diluted net loss per common share is the same for all periods presented because all warrants, stock options and restricted stock units outstanding are anti-dilutive.

	*Three Months Ended March 31,*
	*2024*		*2023*
Common stock warrants		—		7,208,193
Common stock options		10,096,411		5,608,210
Total		10,096,411		12,816,403

Recent Accounting Pronouncements Not Yet Adopted

Note 10 - Related Party Transactions (Details Textual) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended
	May 31, 2023	Apr. 30, 2023	Sep. 20, 2022	Mar. 31, 2023	Mar. 31, 2024	Dec. 31, 2023
Accrued Liabilities, Current					$ 2,268	$ 3,814
Common Stock, Par or Stated Value Per Share (in dollars per share)					$ 0.001	$ 0.001
Loan Agreement [Member]
Debt Instrument, Decrease, Forgiveness		$ 65,000
Interest Payable		$ 200
Robert W. Duggan [Member] \| Private Placement [Member]
Stock Issued During Period, Shares, New Issues (in shares)		10,022,937
Common Stock, Par or Stated Value Per Share (in dollars per share)		$ 0.001
Shares Issued, Price Per Share (in dollars per share)		$ 6.51
Letter Agreement [Member] \| Robert W. Duggan [Member]
Directors and Officers Liability Insurance, Period (Year)				1 year
Related Party Transaction, Amounts of Transaction	$ 1,000		$ 65,000
Accrued Liabilities, Current					$ 0

Condensed Consolidated Statements of Stockholders' Equity (Dificit) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2022	37,235
Balance at Dec. 31, 2022	$ 37	$ 292,420	$ 0	$ (294,705)	$ (2,248)
Issuance of common stock under employee stock purchase plan (in shares)	262
Issuance of common stock under employee stock purchase plan	$ 0	291	0	0	291
Stock-based compensation expense	0	896	0	0	896
Net loss	$ 0	0	0	(9,801)	(9,801)
Issuance of shares upon exercise of warrants (in shares)	96
Issuance of shares upon exercise of warrants	$ 0	194	0	0	194
Balance (in shares) at Mar. 31, 2023	37,593
Balance at Mar. 31, 2023	$ 37	293,801	0	(304,506)	(10,668)
Balance (in shares) at Dec. 31, 2023	55,144
Balance at Dec. 31, 2023	$ 55	381,220	0	(336,915)	44,360
Issuance of common stock under employee stock purchase plan (in shares)	78
Issuance of common stock under employee stock purchase plan	$ 0	296	0	0	296
Issuance of common stock upon exercise of stock options (in shares)	3
Issuance of common stock upon exercise of stock options	$ 0	9	0	0	9
Stock-based compensation expense	0	1,759	0	0	1,759
Net loss	$ 0	0	0	(10,137)	(10,137)
Balance (in shares) at Mar. 31, 2024	55,225
Balance at Mar. 31, 2024	$ 55	$ 383,284	$ 0	$ (347,052)	$ 36,287

Note 9 - Segment Reporting (Details Textual)	3 Months Ended
Note 9 - Segment Reporting (Details Textual)	Mar. 31, 2024
Number of Reportable Segments	1

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

3 Months Ended

Mar. 31, 2024

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

	*Three Months Ended March 31,*
	*2024*		*2023*
Research and development		949		258
General and administrative		810		638
Total stock-based compensation expense	$	1,759	$	896

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

	*Three Months Ended March 31,*
	*2024*		*2023*
Time-based options	$	1,163	$	678
Performance-based options		8		117
Market-based options		507		—
ESPP		81		101
Total stock-based compensation expense	$	1,759	$	896

Share-Based Payment Arrangement, Option [Member]

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

	*Three Months Ended March 31,*
	*2024*		*2023*
Expected term in years		5.3 - 6.3		6.03
Expected volatility		91% - 95%		94%
Risk-free interest rate		4.0% - 4.5%		3.8%
Dividend yield		—		—

	*Three Months Ended March 31,*
	*2024*		*2023*
Expected term in years		5.5 - 5.8		—
Expected volatility		90%		—
Risk-free interest rate		4.2%		—
Dividend yield		—		—

Market-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, 2023		2,100,000	$	6.78		9.44
Options granted		100,000		9.32
Options exercised		—		—
Options canceled		—		—
Options expired		—		—
Balances — March 31, 2024		2,200,000	$	6.89		9.22
Exercisable — March 31, 2024		—		—		—

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, 2023		1,224,130		$	5.51		8.53
Options granted		39,000			8.44
Options exercised		(3,000	)		2.92
Options canceled		(3,000	)		2.92
Options expired		—			—
Balances — March 31, 2024		1,257,130		$	5.61		8.35
Exercisable — March 31, 2024		440,628		$	7.60		7.5

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, 2023		6,141,906		$	10.48		7.07
Options granted		500,000			8.98
Options exercised		—			—
Options canceled		(1,125	)		16.60
Options expired		(1,500	)		17.01
Balances — March 31, 2024		6,639,281		$	10.36		7.05
Exercisable — March 31, 2024		3,580,866		$	14.31		5.15

The 2017 Employee Stock Purchase Plan [Member]

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

	*Three Months Ended March 31,*
	*2024*		*2023*
Expected term in years		0.5 - 1.0		0.5 - 1.0
Expected volatility		98%		83%
Risk-free interest rate		4.9% - 5.3%		5.1% - 5.2%
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, 2023		9,466,036		$	9.01		7.78
Options granted		639,000			9.00
Options exercised		(3,000	)		2.92
Options canceled		(4,125	)		6.65
Options expired		(1,500	)		17.01
Balances — March 31, 2024		10,096,411		$	9.01		7.69
Exercisable — March 31, 2024		4,021,494		$	13.58		5.41

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows from operating activities:
Net loss	$ (10,137)	$ (9,801)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	132	135
Amortization of intangible assets	167	167
Stock-based compensation	1,759	896
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	7	160
Other receivables	(7)	(1)
Right-of-use assets	216	193
Accounts payable	(124)	587
Accrued expenses	(1,546)	496
Deferred revenue	0	4
Lease liabilities	(247)	(207)
Accrued interest on related party note payable	0	801
Net cash used in operating activities	(9,780)	(6,570)
Cash flows from investing activities:
Purchases of property and equipment	(5)	(39)
Net cash used in investing activities	(5)	(39)
Cash flows from financing activities:
Proceeds from issuance of common stock under employee stock purchase plan	296	291
Proceeds from exercises of warrants	0	194
Proceeds from exercises of stock options	9	0
Payments made on related party note	0	(917)
Net cash provided by (used in) financing activities	305	(432)
Net decrease in cash and cash equivalents	(9,480)	(7,041)
Cash and cash equivalents at beginning of period	44,365	61,139
Cash and cash equivalents at end of period	$ 34,885	$ 54,098

Note 6 - Stockholders' Equity and Stock-based Compensation - ESPP Assumptions (Details) - The 2017 Employee Stock Purchase Plan [Member]	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Expected volatility	98.00%	83.00%
Dividend yield	0.00%	0.00%
Minimum [Member]
Expected term in years (Year)	6 months	6 months
Risk-free interest rate	4.90%	5.10%
Maximum [Member]
Expected term in years (Year)	1 year	1 year
Risk-free interest rate	5.30%	5.20%

Note 5 - Goodwill

3 Months Ended

Mar. 31, 2024

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 as the consideration paid exceeded the fair value of the net tangible assets and the intangible assets acquired.

In accordance with ASC Topic 350, Intangibles-Goodwill and Other (as amended by Accounting Standards Update 2017-04), the Company reviews goodwill for impairment at least annually or whenever any events or circumstances indicate that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. The Company performed an updated goodwill impairment analysis as of March 31, 2024, and it was determined that no impairment of goodwill existed.

Note 10 - Related Party Transactions

3 Months Ended

Mar. 31, 2024

10. Related Party Transactions

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, majority stockholder and Executive Chairman, entered into a letter agreement (the “Letter Agreement”) pursuant to which Mr. Duggan agreed with the Company to personally provide indemnity coverage for a one-year period, and he agreed to deposit cash and/or marketable securities into a third-party escrow, as security for these obligations, if requested by the Company. On May 31, 2023, the last day of the one-year period, the Company paid Mr. Duggan a fee of $1.0 million in consideration of the obligations set forth in the Letter Agreement. As of March 31, 2024, there were no additional amounts owed to Mr. Duggan under the Letter Agreement.

On September 20, 2022, the Company and Robert W. Duggan, the Company's 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. On April 30, 2023, the Company entered into a Securities Purchase Agreement with Mr. Duggan, pursuant to which the Company agreed to issue and sell to Mr. Duggan 10,022,937 shares of the Company’s common stock, par value $0.001 per share, in a Private Placement, at a price per share of $6.51. These shares were paid for through the cancellation of the amounts then owed by the Company under the 2022 Loan Agreement, the principal sum of $65.0 million and all accrued and unpaid interest outstanding, which totaled approximately $0.2 million as of April 30, 2023. Upon closing of the Private Placement and satisfaction of the outstanding debt, the 2022 Loan Agreement terminated, without early termination fees or penalties being owed by the Company. No additional amounts are owed to Mr. Duggan under the 2022 Loan Agreement. See Note 8 for further details.

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483326/850-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
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-Topic 850
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-Topic 850
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-URI https://asc.fasb.org/1943274/2147483326/850-10-50-1

Note 6 - Stockholders' Equity and Stock-based Compensation - Stock-based Compensation Expense by Type (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Total stock-based compensation expense	$ 1,759	$ 896
Time-based Options [Member]
Total stock-based compensation expense	1,163	678
Performance-based Options [Member]
Total stock-based compensation expense	8	117
Market-based Options [Member]
Total stock-based compensation expense	507	0
Employee Stock Purchase Plan Award [Member]
Total stock-based compensation expense	$ 81	$ 101

Note 7 - Research Grants and Agreements (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Research and Development Expense	$ 6,741	$ 5,829
Old Dominion University Research Foundation [Member] \| Sponsored Research Agreement SRA [Member]
Research and Development Expense	$ 0	$ 0

Note 2 - Summary of Significant Accounting Policies - Warrant Accrual Activity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Beginning balance	$ 0	$ 50
Add: Accruals for warranties issued during the period	0	0
Less: Adjustment for inventory at cost and excessive and obsolete inventory	0	0
Ending balance	$ 0	$ 50

Note 11 - Restructuring Charges (Details Textual) $ in Thousands	1 Months Ended	3 Months Ended
	Feb. 28, 2023 USD ($)	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)
Income Statement [Abstract]
Costs and Expenses		$ 10,615	$ 9,562
Restructuring Charges, Statement of Income or Comprehensive Income [Extensible Enumeration]			Costs and Expenses
Employee Severance [Member]
Restructuring and Related Cost, Number of Positions Eliminated	7
Restructuring Charges	$ 100

Note 2 - Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2024

Schedule of Product Warranty Liability [Table Text Block]

	*Three Months Ended March 31,*
	*2024*		*2023*
Beginning balance	$	—	$	50
Add: Accruals for warranties issued during the period		—		—
Less: Adjustment for inventory at cost and excessive and obsolete inventory		—		—
Ending balance	$	—	$	50

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

	*Three Months Ended March 31,*
	*2024*		*2023*
Common stock warrants		—		7,208,193
Common stock options		10,096,411		5,608,210
Total		10,096,411		12,816,403

Note 6 - Stockholders' Equity and Stock-based Compensation - Stock-based Compensation Expense by Recorded Location (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Total stock-based compensation expense	$ 1,759	$ 896
Research and Development Expense [Member]
Total stock-based compensation expense	949	258
General and Administrative Expense [Member]
Total stock-based compensation expense	$ 810	$ 638

Note 11 - Restructuring Charges - USD ($) $ in Thousands	3 Months Ended
Note 11 - Restructuring Charges - USD ($) $ in Thousands	Mar. 31, 2024	Mar. 31, 2023
Income Statement [Abstract]
Costs and Expenses	$ 10,615	$ 9,562
Notes to Financial Statements
Restructuring and Related Activities Disclosure [Text Block]	*11.* Restructuring Charges In February 2023, the Company eliminated seven positions and incurred a discrete restructuring related charge of $0.1 million which was fully recorded in February 2023 and the related expenses are included within total cost and expenses on the condensed consolidated statement of operations for the three months ended March 31, 2023. This charge represents the total amount incurred in connection with the activity.

Note 4 - Balance Sheet Components - Schedule of Amortization of Intangible Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
2024 (remaining 9 months)	$ 498
2025	665
2026	556
Total	$ 1,719	$ 1,886

Note 7 - Research Grants and Agreements

3 Months Ended

Mar. 31, 2024