The Company has stock-based compensation plans under which it grants stock options, restricted stock units ("RSUs"), and performance restricted stock units ("PRSUs") to officers, directors and third parties. Total stock-based compensation for the periods presented are as follows (in thousands):


	Three Months Ended
	March 31,
	2024		2023
Cost of sales	$	483	$	6,006
Research and development		4,315		1,317
Sales, general and administrative		12,524		9,139
Total	$	17,322	$	16,462

As of March 31, 2024, there was $100.9 million of unrecognized compensation expense for RSUs and PRSUs to be recognized over a weighted average period of 1.97 years.

The Company issued approximately 3,154,000 and 1,967,000 shares of common stock, before net share settlement, upon vesting of RSUs and PRSUs during the three months ended March 31, 2024 and 2023, respectively.

Employees are eligible to participate in the Employee Stock Purchase Plan ("ESPP") approved by its shareholders. During the three months ended March 31, 2024 and 2023, there were no shares issued under the ESPP.

The Company estimates the fair value of shares issued to employees under the ESPP using the Black-Scholes option-pricing model. The assumptions used to estimate the fair value of stock options granted and stock purchase rights under the ESPP are as follows:


	Three Months Ended
	March 31,
	2024			2023
Risk-free interest rate		5.41	%		4.54	%
Expected dividend yield		—			—
Expected term (years)		0.50			0.60
Volatility		58.41	%		62.77	%

In connection with debt financing entered into with Squadron Medical in 2018, and amended in 2019 and 2020, the Company issued common stock warrants to Squadron Medical and a participant lender (the “Squadron Medical Warrants”). The Squadron Medical Warrants expire in May 2027 and are exercisable by cash exercise. No Squadron Medical Warrants have been exercised as of March 31, 2024.

The Company issued warrants to the Company’s Chairman and Chief Executive Officer (the “Executive Warrants”). The Executive Warrants had a five-year term and are exercisable by cash or cashless exercise. In October 2022, the term was extended to seven years. No Executive Warrants have been exercised as of March 31, 2024.

A summary of all outstanding warrants for common stock as of March 31, 2024, are as follows (in thousands, except for strike price data):


	Number of Warrants		Strike Price		Expiration
2018 Squadron Medical Warrants		845	$	3.15	May 2027
2019 Squadron Medical Warrants		4,839	$	2.17	May 2027
2020 Squadron Medical Warrants		1,076	$	4.88	May 2027
Executive Warrants		1,327	$	5.00	December 2024
Other(1)		129	$	10.10	Various through June 2026
Total		8,216

(1)

Weighted-average strike price.

All outstanding warrants were deemed to qualify for equity classification under authoritative accounting guidance.