Note 13 - Stock-based Compensation

12 Months Ended

Dec. 31, 2023

Notes to Financial Statements

Share-Based Payment Arrangement [Text Block]

13.         Stock-Based Compensation

Incentive Compensation Plan Information

On June 6, 2023, at the 2023 Annual Meeting of Stockholders, the Company’s stockholders voted to approve an amendment and restatement of the Company’s Incentive Compensation Plan (“the Plan”) to increase the number of shares reserved for issuance under the Plan by 22,000,000 shares. As of December 31, 2023, there were 54,072,307 shares authorized for issuance, and 22,185,899 shares available for future issuance under the Plan. To date all equity awards under the Plan have consisted of nonqualified stock options, incentive stock options, restricted stock units and stock awards.

Under the Plan, which is administered by the Compensation Committee, the Company may grant stock options, stock appreciation rights, restricted stock units, restricted stock or stock awards to employees, officers, non-employee directors, consultants, and vendors. The exercise price of stock options or stock appreciation rights may not be less than the fair market value of the Company’s shares at the date of grant. Additionally, no stock options or stock appreciation rights granted under the Plan may have a term exceeding ten years.

Stock Options

The following table summarizes the Company’s stock option activity, including grants to non-employees, for the year ended December 31, 2023:

	Number of Shares			Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)
Balance at December 31, 2022		7,584,967		$	4.22		5.31
Granted		3,047,615			0.71
Forfeited		(149,430	)		0.78
Cancelled		(25,173	)		27.32
Exercised		(13,300	)		0.38
Balance at December 31, 2023		10,444,679		$	3.20		4.80

The weighted-average grant date fair value of stock options was $0.59 during the years ended December 31, 2023 and 2022. The aggregate intrinsic value of stock options exercised under the Company’s stock plans was not material during the years ended December 31, 2023 and 2022.

The following table summarizes information about stock options outstanding at December 31, 2023:

	Number of Shares		Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (Millions)
Exercisable at December 31, 2023		5,726,280	$	5.02		4.12	$	-
Vested or expected to vest at December 31, 2023		10,105,084	$	3.28		4.77	$	-

The fair value of options granted were estimated using the Black-Scholes-Merton option pricing model based on the assumptions in the table below:

	Years Ended December 31,
	2023			2022
Expected dividend yield		0%			0%
Expected volatility	124%	-	130%	126%	-	133%
Risk-free interest rate	3.53%	-	4.14%	1.25%	-	4.40%
Expected life (in years)	3.8	-	4.5	3.8	-	4.5

Restricted Stock Units

The following is a summary of the restricted stock unit activity, including performance restricted stock units, for the year ended December 31, 2023:

	Number of Restricted Stock Units Outstanding			Weighted-Average Grant Date Fair Value
Unvested December 31, 2022		8,483,491		$	1.04
Granted		8,616,931			0.70
Vested		(3,937,130	)		1.10
Forfeited		(837,115	)		0.76
Unvested December 31, 2023		12,326,177		$	0.81

Performance Restricted Stock Units

In 2023 and 2022, the Company granted performance-based restricted stock units (“PRSUs”). The number of shares earnable under the 2023 and 2022 awards were based on achieving certain operational targets by December 31, 2023 (for the PRSUs granted in 2023) and October 1, 2023 (for the PRSUs granted in 2022), respectively. In February 2024, the Board determined that the operational targets for PRSU awards granted in 2023 were 50% achieved and as a result, the 2023 PRSUs were 50% earned and remain subject to three-year time-based vesting requirements. The other 50% of the 2023 PRSUs were forfeited. The operational targets were achieved for the PRUSs granted in 2022, therefore the 2022 PRSUs were fully earned and remain subject to three-year time-based vesting requirements.

Stock-based Compensation Expense

The following table summarizes non-cash stock-based compensation expense by award type for the years ended December 31, 2023, and 2022:

	Years Ended December 31,
	2023		2022
	(in thousands)
Stock options	$	2,338	$	3,654
Restricted stock units		3,954		3,319
Performance restricted stock units		1,626		1,443
	$	7,918	$	8,416

As of December 31, 2023, the unrecognized stock-based compensation expense related to unvested stock options was approximately $1.6 million, which is expected to be recognized over an estimated weighted-average period of 1.4 years. As of December 31, 2023, the unrecognized stock-based compensation expense related to unvested restricted stock units and performance restricted stock units was approximately $4.4 million, which is expected to be recognized over a weighted average period of approximately 1.2 years.