The Company maintains a stock-based compensation plan, the 2011 Incentive Compensation Plan (the “2011 Plan”), as amended, to attract, motivate, retain and reward employees, directors and consultants by providing its Board or a committee of the Board the discretion to award equity incentives to these persons.

A summary of stock option activity for the three months ended March 31, 2022 is as follows:

	Number Outstanding			Average Exercise Price per Share		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Balance as of December 31, 2021		514,693		$	5.11		4.11	$	11,850,930
Granted		—			—
Cancelled or Expired		(333	)		19.70
Exercised		—			—
Balance as of March 31, 2022		514,360		$	5.11		3.87	$	5,691,347
Vested or expected to vest as of March 31, 2022		514,360		$	5.11		3.87	$	5,691,347
Exercisable as of March 31, 2022		514,360		$	5.11		3.87	$	5,691,347

The aggregate intrinsic value in the table above represents the difference between the fair value of the Company’s common stock as of March 31, 2022 and the exercise price of in-the-money stock options multiplied by the number of such stock options.

The following table summarizes information about stock options outstanding as of March 31, 2022:

	Stock Options Outstanding						Stock Options Exercisable
Range of Exercise Prices	Number Outstanding		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price		Number Exercisable		Weighted Average Exercise Price
$4.36 - $7.20		452,510		4.12	$	4.41		452,510	$	4.41
$7.50 - $11.25		61,317		1.98		10.19		61,317		10.19
$11.30 - $16.95		500		2.00		11.30		500		11.30
$19.70 - $29.55		33		1.38		19.70		33		19.70
$4.36 - $29.55		514,360		3.87	$	5.11		514,360	$	5.11

As of March 31, 2022, there was no unrecognized stock-based compensation expense related to stock options.

The following is a summary of RSU activity for the three months ended March 31, 2022:

	Number Outstanding			Weighted Average Fair Value
Unvested as of December 31, 2021		485,729		$	9.19
Granted		144,738			20.89
Vested		(71,310	)		7.84
Forfeited		(1,844	)		11.71
Unvested as of March 31, 2022		557,313		$	12.40
RSUs vested but not released		301,439		$	5.48

The fair value of the Company’s RSUs is calculated based upon the fair market value of the Company’s common stock at the date of grant. As of March 31, 2022, there was $5.6 million of unrecognized compensation expense related to unvested RSUs granted, which is expected to be recognized over a weighted average period of 3.3 years. No tax benefit was realized from RSUs for the three months ended March 31, 2022.

The Company granted 200,000 PSUs to a certain key employee during the year ended December 31, 2020, with a grant date fair value of $6.38 per share. The PSUs are subject to the attainment of performance goals established by the Company’s Compensation Committee, the periods during which performance is to be measured, and other limitations and conditions. Performance goals are based on pre-established objectives that specify the manner of determining the number of PSUs that will vest if performance goals are attained. If the employee terminates employment, the non-vested portion of the PSUs will not vest and all rights to the non-vested portion will terminate.

The following is a summary of PSU activity for the three months ended March 31, 2022:

	Number Outstanding
Unvested as of December 31, 2021		175,000
Granted		—
Vested		(20,000	)
Forfeited		(80,000	)
Unvested as of March 31, 2022		75,000

As of March 31, 2022, there was $0.4 million of unrecognized compensation expense related to unvested PSUs, which is expected to be recognized over a period of 0.8 years. No tax benefit was realized from PSUs for the three months ended March 31, 2022.

The following table summarizes stock-based compensation expense related to stock options, RSUs, and PSUs included in the condensed consolidated statements of comprehensive loss for the three months ended March 31, 2022 and 2021 (in thousands):

	Three Months Ended March 31,
	2022		2021
Cost of revenue	$	56	$	33
Research and development		310		162
Selling and marketing		194		103
General and administrative		335		460
Total	$	895	$	758

During the three months ended March 31, 2022 and 2021, the Company repurchased 17,647 and 25,327 shares, respectively, of common stock surrendered to the Company to satisfy tax withholding obligations in connection with the vesting of RSUs issued to employees.