The Company maintains a stock incentive plan, which permits the granting of incentive stock options or nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance awards, and other stock-based awards. The equity-based awards will vest over a four-year period for all employees. The initial equity-based awards granted to the Company’s non-employee, independent directors upon appointment to the board of directors will vest over a three-year period and the annual equity-based awards granted to the Company’s non-employee, independent directors granted thereafter will cliff vest after one year from the date of grant.

The following table summarizes the stock option activity for the six months ended June 30, 2022 (in thousands, except share and per share data):


	Number of Shares			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at January 1, 2022		2,764,112		$	4.63		8.69	$	45,280
Granted		916,150		$	14.98
Exercised		(55,232	)	$	1.79
Cancelled or forfeited		(108,969	)	$	10.09
Outstanding at June 30, 2022		3,516,061		$	7.20		8.54	$	15,798
Exercisable at June 30, 2022		1,068,360		$	2.62		8.20	$	6,946
Vested and expected to vest at June 30, 2022		3,231,379		$	7.80		8.72	$	13,536

The weighted average assumptions used in the Black-Scholes pricing model for stock options granted during the three and six months ended June 30, 2022 were as follows:


	For the Three Months Ended June 30,						For the Six Months Ended June 30,
	2022			2021			2022			2021
Estimated dividend yield	-%			-%			-%			-%
Weighted-average expected stock price volatility		33.47	%		33.86	%		33.14	%		35.28	%
Weighted-average risk-free interest rate		2.90	%		1.05	%		2.09	%		0.91	%
Expected average term of options (in years)		6.25			5.85			6.25			5.92
Weighted-average fair value of common stock	$	14.11		$	16.00		$	14.98		$	15.23
Weighted-average fair value per option	$	5.44		$	5.42		$	5.48		$	4.52

The following table summarizes the restricted stock unit activity for the six months ended June 30, 2022 (in thousands, except share and per share data):


	Number of Shares		Weighted Average Grant Date Fair Value per Share
Outstanding at January 1, 2022		—	$	—
Granted		28,071	$	7.43
Vested		—	$	—
Forfeited		—	$	—
Outstanding at June 30, 2022		28,071	$	7.43

The Company also maintains an employee stock purchase plan (ESPP) that authorizes the issuance of shares of common stock pursuant to purchase rights granted to eligible employees. Unless otherwise determined by the Company’s board of directors, shares of the Company’s common stock will be purchased for the accounts of employees participating in the Company’s ESPP at a price per share equal to the lesser of (i) 85% of the fair market value of a share of the Company’s common stock on the first day of an offering; or (ii) 85% of the fair market value of a share of the Company’s common stock on the date of purchase. The Company issued 13,235 shares of common stock under the ESPP during the three and six months ended June 30, 2022.

Stock-based compensation expense included in the accompanying condensed financial statements was as follows (in thousands):


	For the Three Months Ended June 30,				For the Six Months Ended June 30,
	2022		2021		2022		2021
Cost of sales	$	44	$	—	$	63	$	—
Research and development		48		50		113		77
Sales and marketing		126		30		225		52
General and administrative		716		222		1,320		356
Total stock-based compensation expense	$	934	$	302	$	1,721	$	485

Stock-based compensation expense related to stock options was $0.9 million and $0.3 million for the three months ended June 30, 2022 and 2021, respectively and $1.7 million and $0.5 million for the six months ended June 30, 2022 and 2021, respectively. Unrecognized compensation expense related to stock options was $11.1 million at June 30, 2022, which is expected to be recognized as expense over the weighted-average period of 3.19 years.

Stock-based compensation expense related to restricted stock units was not significant for the three and six months ended June 30, 2022 and 2021. Unrecognized compensation expense related to restricted stock units was $0.2 million at June 30, 2022, which is expected to be recognized as expense over the weighted-average period of 0.92 years.

Stock-based compensation expense related to the ESPP was not significant for the three and six months ended June 30, 2022 and 2021. Total compensation cost related to the ESPP not yet recognized also was not significant. As of June 30, 2022, an insignificant amount has been withheld on behalf of employees for future purchase under the ESPP.