Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2022

Stock-based Compensation [Abstract]

Stock Option Activity

The following table summarizes stock option activity for the six months ended June 30, 2022:

	Number of shares			Weighted average exercise price per share		Weighted average remaining contractual term (years)
Outstanding at January 1, 2022		3,938,613		$	1.90
Granted		970,000		$	1.43
Exercised		(15,000	)	$	1.29
Forfeited and expired		(348,899	)	$	2.97
Outstanding at June 30, 2022		4,544,714		$	1.72		8.5
Exercisable at June 30, 2022		1,532,912		$	1.92		7.4
Vested and expected to vest		4,544,714		$	1.72		8.5

Weighted Average Assumption Used for Grant Date Fair Value of Option Grants

For the six months ended June 30, 2022, the fair value of each option was estimated on the date of grant using the weighted average assumptions in the table below:

Expected volatility	89.6	%
Risk‑free interest rate	2.5	%
Expected term (in years)	6.1
Expected dividend yield	0.0	%

Summary of Restricted Stock Unit Unvested

Restricted stock units have been issued to certain board members. Restricted stock units unvested are summarized in the following table:

	Number of shares			Weighted average grant date fair value
Unvested at January 1, 2022		90,540		$	1.45
Granted		28,003		$	1.13
Vested		(43,003	)	$	1.24
Unvested at June 30, 2022		75,540		$	1.45