Equity Incentive Plans (Tables)

6 Months Ended

Jun. 30, 2022

Equity Incentive Plans [Abstract]

Stock Option Plan Activity

Activity under the stock option plans was as follows:

	Number of options			Weighted average exercise price		Weighted average remaining contracted term in years		Aggregate intrinsic value
Outstanding at December 31, 2021		689,995		$	3.58			$	683,531
Granted		270,170			6.71
Expired		(3,334	)		27.00
Forfeited		(834	)		6.12
Outstanding at March 31, 2022		955,997		$	4.38		6.47	$	125,279
Granted		51,000			1.50
Exercised		(9,445	)		1.71
Expired		(278	)		27.00
Forfeited		(46,668	)		3.27
Outstanding at June 30, 2022		950,606		$	4.30		6.55	$	181,745
Vested and exercisable at June 30, 2022		476,941		$	3.71		5.08	$	57,557

Estimated Using Assumptions

The weighted-average fair values of the options granted to employees and nonemployees were $2.34 and $1.55, respectively and were estimated using the following weighted-average assumptions:

	Employee			Nonemployee
Expected term (in years)		6.47			5.63
Risk‑free interest rate		1.74	%		2.67	%
Dividend yield		—	%		—	%
Expected volatility		107.23	%		109.67	%

The fair value of the inducement grant was $2.46 and was estimated using the following assumptions:

	Inducement
Expected term (in years)		6.25
Risk‑free interest rate		1.76	%
Dividend yield		—	%
Expected volatility		106.76	%

Share-based Compensation Expense

The following table shows the share-based compensation expense related to vested stock option grants to employees and nonemployees by financial statement line item on the accompanying statement of comprehensive loss:

	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development	$	33,436		29,205		62,575		64,702
Sales and marketing		1,216		936		2,342		1,861
General and administrative		27,515		27,905		41,609		63,973
Total share-based compensation expense	$	62,167		58,046		106,526		130,536