The Company has various share-based compensation plans, including the Third Amended and Restated 2017 Equity Incentive Plan, the 2013 Non-Employee Directors’ Equity Incentive Plan and the 2021 Inducement Plan (collectively, the “Plans”). The Plans are designed to assist in attracting, motivating, and retaining employees and directors and to recognize the importance of employees to the long-term performance and success of the Company. The Company has also granted stock options to certain non-employees outside of the Plans.

The Company recognized stock-based compensation expense related to grants of stock options and common stock awards to employees, directors and consultants of $670,000 and $862,000 during the years ended December 31, 2023 and 2022, respectively. The following table summarizes the stock-based compensation expense that was recognized in the consolidated statements of operations for the years ended December 31,

The majority of the common stock awards and options to purchase common stock vest on the anniversary of the date of grant, which ranges from one to four years. Stock-based compensation expense related to these awards is recognized on a straight-line basis over the related vesting term in most cases, which generally is the service period. It is the Company’s policy to issue new shares upon the exercise of options.

For options outstanding and vested at December 31, 2023 and 2022, the weighted average remaining contractual life was 9.18 years and 8.79 years, respectively. There were no option exercises in 2023 or 2022. The total fair value of options that vested in 2023 and 2022 was $614,100, and $1.1 million, respectively, at the fair value of the options as of the date of grant.

Valuation Assumptions: The fair value of each stock option is estimated at the grant date using the Black-Scholes option pricing model. The fair value of stock options under the Black-Scholes option pricing model requires management to make assumptions regarding projected employee stock option exercise behaviors, risk-free interest rates, volatility of the Company’s stock price, and expected dividends.

The Company has not historically paid cash dividends to its common stockholders and currently does not anticipate paying any cash dividends in the foreseeable future. As a result, the Company has assumed a dividend yield of 0%. The risk-free interest rate is based upon the rates of U.S. Treasury bills with a term that approximates the expected life of the option. Since the Company has limited historical exercise data to reasonably estimate the expected life of its option awards, the expected life is calculated using a simplified method. Expected volatility is based on historical volatility of the Company’s stock.

The following table provides the weighted average assumptions used in the Black-Scholes option pricing model for the years ended December 31:

The weighted-average fair value of stock options granted in 2023 and 2022 was $6.09 and $76.05, respectively. As of December 31, 2023, the total compensation cost related to all non-vested stock option awards not yet recognized was approximately $1.1 million and is expected to be recognized over the remaining weighted-average life of 3.01 years.

Warrants: Warrants to purchase 2,963 and 679 shares of common stock were outstanding on December 31, 2023 and 2022, respectively. Exercisable warrants were 151,583 and 679,244 on December 31, 2023 and 2022, respectively. As of December 31, 2023, warrants outstanding were exercisable at prices ranging from $3.30 to $189,000 per share and are exercisable over a period ranging from immediately to 4.8 years.