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Stock-Based Compensation (Tables)
12 Months Ended
Dec. 31, 2024
Stock-Based Compensation [Abstract]  
Components of Stock-Based Compensation Expense
Following is the stock-based compensation expense related to common stock options, restricted common stock, common stock warrants and deferred stock units:

   
Year Ended
December 31,
 
   
2024
   
2023
 
Research and development
 
$
1,222
   
$
829
 
General and administrative
   
1,225
     
1,432
 
Total stock-based compensation expense
 
$
2,447
   
$
2,261
 
Weighted Average Assumptions Used to Determine Fair Value of Options Granted
The fair value of the options granted is determined using the Black-Scholes option-pricing model. The following weighted average assumptions were used:

   
2024
   
2023
 
Risk-free interest rate
   
3.89
%
   
3.84
%
Expected life of the options
 
5.4 years
   
5.7 years
 
Expected volatility of the underlying stock
   
75.1
%
   
85.6
%
Expected dividend rate
   
0
%
   
0
%
Stock Option Activity
The following table summarizes the stock option activity in the stock-based compensation plans:

   
Number of
Shares
   
Weighted
Average
Exercise
Price
     
Weighted
Average
Remaining
Contractual
Life
(in years)
        
Aggregate
Intrinsic Value
(in thousands)
 
Outstanding, December 31, 2022
   
5,745,561
   
$
2.90
                         
Granted
   
1,025,000
     
1.18
                         
Forfeited/Cancelled
   
(436,720
)
   
2.23
                         
Exercised
   
   
                         
Outstanding, December 31, 2023
   
6,333,841
   
$
2.66
                         
Granted
   
1,373,000
     
1.86
                         
Forfeited/Cancelled
   
(348,750
)
   
6.35
                         
Exercised
   
(503,333
)
   
1.71
                         
Outstanding, December 31, 2024
   
6,854,758
   
$
2.39
     
6.27
     $
183
 
Exercisable, December 31, 2024
   
6,138,254
    $ 2.45      
6.00
     $
176
 
Outstanding and Exercisable Options under Stock Based Compensation Plans
The following table summarizes additional information regarding outstanding and exercisable options under our stock-based compensation plans at December 31, 2024:

     
Options Outstanding
   
Options Exercisable
 
Exercise
Price (Range)
   
Number of
Shares
   
Weighted
Average
Remaining
Contractual
Life
   
Weighted
Average
Exercise
Price
   
Number of
Shares
   
Weighted
Average
Exercise
Price
 
           
(in years)
                   
$0.89 – 1.50
     
1,134,206
     
7.13
   
$
1.16
     
934,202
   
$
1.12
 
$1.51 – 2.50
     
3,691,315
     
6.88
     
2.02
     
3,199,815
     
2.02
 
$2.51 – 5.00
     
1,809,237
     
4.88
     
3.48
     
1,784,237
     
3.48
 
$5.01 – 6.71
     
220,000
     
3.10
     
5.92
     
220,000
     
5.92
 
        
6,854,758
     
6.27
   
$
2.39
     
6,138,254
   
$
2.45