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Stock-based Compensation (Tables)
 12 Months Ended
Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]  
Summary Of Activity For The Company's Restricted Shares
SharesWeighted- Average Grant-Date Fair Value
Unvested at December 31, 202217,252 $4.87 
Granted24,524 0.64 
Vested(7,562)7.34 
Forfeited(8,332)5.21 
Unvested at December 31, 202325,882 $5.69 
The activity for performance-based restricted stock units in the year ended December 31, 2023 was as follows (in thousands, except weighted-average grant-date fair value amounts):

SharesWeighted- Average Grant-Date Fair Value
Unvested at December 31, 202214,160 $4.80 
Granted— — 
Vested— — 
Forfeited(1,656)3.00 
Unvested at December 31, 202312,504 $2.67 
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award The Company estimated the fair value of the August and September Initial Loans, as defined in Note 9, based on assumptions used in the Monte Carlo simulation model using the following inputs as of the end of the reporting period:
August Convertible DebentureSeptember Convertible Debenture
Expected term (in years)0.750.90
Stock price$0.26 $0.26 
Interest rate3.0 %3.0 %
Expected volatility121.3 %121.0 %
Expected dividend rate— — 
Risk free rate5.0 %4.8 %
The following table summarizes the Company’s total stock-based compensation expense by line item for the years ended December 31, 2023 and 2022 (in thousands):
Year Ended December 31,
20232022
Research and development$6,711 $31,083 
Selling, general and administrative23,495 48,490 
Total
$30,206 $79,573 
The fair value of the warrants at the issuance date was measured using the Black-Scholes-Merton option pricing model. The key inputs used in the valuation were as follows:
Expected term (years)10.0
Risk free interest rate3.0 %
Expected volatility91.3 %
Dividend yield— %
Exercise price$2.15 
Stock price$3.63 
The fair value of the warrants at the expiration of the option period was measured using the Black-Scholes-Merton option pricing model. The key inputs used in the valuation were as follows:
Expected term (years)0.9
Expected volatility116.4 %
Dividend yield— %
Risk free rate4.7 %
Estimated fair value per warrant$0.57 
Exercise price$1.05 
Stock price$1.20 
        
The fair value of the warrants was measured using the Black-Scholes-Merton option pricing model. The key inputs used in the valuation were as follows:
Expected term (years)4.6
Expected volatility121.7 %
Expected dividend rate— %
Risk free rate3.8 %
Estimated fair value per warrant$0.16 
Exercise price$1.30 
Stock price$0.26 
The warrants are liability classified and subject to periodic remeasurement. The fair value of the warrants was measured using the Black-Scholes option pricing model. The key inputs used in the valuation were as follows:

Expected term (years)5.0
Expected volatility121.7 %
Expected dividend rate— %
Risk free rate3.8 %
Estimated fair value per warrant$0.19 
Exercise price$0.67 
Stock price$0.26 
The warrants are liability classified and subject to periodic remeasurement. The fair value of the warrants was measured using the Black-Scholes option pricing model. The key inputs used in the valuation were as follows:

Expected term (years)4.8
Expected volatility121.7 %
Expected dividend rate— %
Risk free rate3.8 %
Estimated fair value per warrant$0.19 
Stock Price$0.26 
Exercise Price$0.65 
The key inputs used in the valuation were as follows:
Expected term (years)5.1
Expected volatility121.7 %
Expected dividend rate— %
Risk free rate3.8 %
Estimated fair value per warrant$0.19 
Exercise price$0.67 
Stock price$0.26 
The key inputs used in the valuation on October 5, 2023 were as follows:
July Convertible DebentureAugust Convertible DebentureSeptember Convertible Debenture
Expected term (years)4.74.85.0
Expected volatility108.0 %108.0 %108.0 %
Expected dividend rate— %— %— %
Risk free rate4.6 %4.6 %4.6 %
Estimated fair value per warrant$0.34 $0.34 $0.34 
Exercise price$0.54 $0.54 $0.54 
Stock price$0.44 $0.44 $0.44 
The key inputs used in the valuation were as follows:
Expected term (years)4.8
Risk free rate3.8 %
Expected volatility121.7 %
Expected dividend rate— %
Exercise price$0.56 
Stock price$0.26 
Estimated fair value per warrant$0.19