Note 5 - Warrant Liabilities

6 Months Ended

Jun. 30, 2025

Notes to Financial Statements

Warrant Liabilities Disclosure [Text Block]

5. Warrant Liabilities

On August 11, 2022, the Company issued warrants (the "Notes Warrants") to purchase Common Stock in conjunction with a senior secured convertibles notes (the "Notes") and warrants offering (the "Notes and Warrants Offering"), at an initial fair value of $3.8 million. The Notes sold by the Company in the Notes and Warrants Offering were subsequently retired upon maturity at December 31, 2023. The exercise price of and number of shares underlying the Notes Warrants were immediately proportionately adjusted pursuant to the Reverse Stock Split to $26.80 and 279,851 shares, respectively, and on May 2, 2024, the exercise price for each of the Notes Warrants was further adjusted to $2.06 in accordance with their terms.

The Company issued additional warrants (the "Additional Warrants") to purchase Common Stock on August 12, 2022 in conjunction with a registered direct offering for the sale of shares of the Company's Common Stock and the Additional Warrants. The Additional Warrants do not reprice further beyond the immediate proportionate adjustments to the per share exercise price and number of shares issuable of $21.20 and 141,509 shares, respectively, that occurred upon and as a result of the Reverse Stock Split.

All changes in the fair value of the Notes Warrants and Additional Warrants liabilities are recognized in the Company's consolidated statements of operations until they are either exercised or expire. Since their issuance, none of the Notes Warrants or Additional Warrants have been exercised. The Notes Warrants and Additional Warrants are not traded in an active securities market and, as such, the estimated fair value is determined by using a Black-Scholes option pricing model which considers the likelihood of repricing adjustments and utilizes assumptions noted in the following table. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of valuation. Expected volatility is based on the historical volatility over the expected remaining term of the warrants. The Company has no reason to believe future volatility over the expected remaining life of the Notes Warrants and Additional Warrants is likely to differ materially from historical volatility. Expected life is based on the term of the applicable warrants. Below are the specific assumptions utilized (unaudited, except for December 31, 2024):

Notes Warrants	June 30, 2025			December 31, 2024
Common stock market price	$	0.86		$	1.31
Risk-free interest rate		3.9	%		4.2	%
Expected dividend yield		—			—
Expected term (in years)		2.12			2.61
Expected volatility		117.3	%		105.9	%

Additional Warrants	June 30, 2025			December 31, 2024
Common stock market price	$	0.86		$	1.31
Risk-free interest rate		3.9	%		4.3	%
Expected dividend yield		—			—
Expected term (in years)		2.62			3.12
Expected volatility		112.7	%		99.6	%