Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Stock-Based Compensation [Abstract]

Components of Stock-Based Compensation Expense

Following is the stock-based compensation expense related to common stock options, restricted common stock, common stock warrants and deferred stock units:

	Year Ended December 31,
	2021		2020
Research and development	$	420	$	516
General and administrative		1,656		1,283
Total stock-based compensation expense	$	2,076	$	1,799

Weighted Average Assumptions Used to Determine Fair Value of Options Granted

The fair value of the options granted is determined using the Black-Scholes option-pricing model. The following weighted average assumptions were used:

	2021			2020
Risk-free interest rate		0.66	%		1.26	%
Expected life of the options	6.0 years			6.0 years
Expected volatility of the underlying stock		91.7	%		97.9	%
Expected dividend rate		0	%		0	%

Stock Option Activity

The following table summarizes the stock option activity in the stock-based compensation plans:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2019		3,000,256		$	4.88
Granted		1,095,000			2.51
Forfeited/Cancelled		(23,057	)		1.80
Exercised		(84,624	)		2.61
Outstanding, December 31, 2020		3,987,575		$	4.29
Granted		2,660,000			2.39
Forfeited/Cancelled		(1,603,073	)		5.31
Exercised		(148,941	)		2.35
Outstanding, December 31, 2021		4,895,561		$	3.14		7.94	$	246
Exercisable, December 31, 2021		2,158,477		$	4.09		6.29	$	169

Outstanding and Exercisable Options under Stock Based Compensation Plans

The following table summarizes additional information regarding outstanding and exercisable options under our stock-based compensation plans at December 31, 2021:

	Options Outstanding						Options Exercisable
Exercise Price (Range)	Number of Shares		Weighted Average Remaining Contractual Life		Weighted Average Exercise Price		Number of Shares		Weighted Average Exercise Price
			(in years)
$0.87 – 1.00		120,500		4.96	$	0.89		120,500	$	0.89
$1.01 – 3.00		3,404,521		8.65		2.32		962,437		2.54
$3.01 – 5.00		1,013,040		7.12		4.14		718,040		4.36
$5.01 – 8.00		220,000		6.11		5.92		220,000		5.92
$8.01 – 13.38		137,500		2.06		13.38		137,500		13.38
		4,895,561		7.94	$	3.14		2,158,477	$	4.09