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Stock-based Compensation (Tables)
 3 Months Ended
Mar. 31, 2022
Share-based Payment Arrangement [Abstract]  
Stock Option Activity
The following table summarizes stock option activity during the three months ended March 31, 2022:
Options
Weighted-
Average
Exercise
Price
Weighted-
Average
Remaining
Contractual
Term
Aggregate
Intrinsic
Value
Outstanding at January 1, 2022
3,156,379 $9.45 7.55$5,720 
Granted2,122,976 3.68 
Exercised— — 
Forfeited(10,043)48.15 
Outstanding at March 31, 2022
5,269,312 $7.05 8.30$4,131,736 
Exercisable at March 31, 2022
1,608,347 $10.84 6.03$111,672 
Assumptions used in Black-Scholes Pricing Model for New Grants The following tables summarize the assumptions used in the Black-Scholes option-pricing model in the three months ended March 31, 2022 and 2021:
 Three Months Ended
March 31,
 20222021
Volatility factor
97.19% - 97.79%
56.17% - 102.66%
Expected term (in years)
6.25
0.25 - 6.25
Risk-free interest rates
1.69% - 2.20%
0.06% - 1.13%
Dividend yield——