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Stock-Based Compensation (Tables) | 12 Months Ended
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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 |

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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 718 -SubTopic 10 -Subparagraph (f)(2) -Name Accounting Standards Codification -Paragraph 2 -Section 50 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 + Details
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