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Stockholders' Equity (Tables) | 3 Months Ended
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Mar. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Summary of Stock Option Activities | The following table summarizes stock option activities for the three months ended March 31, 2022: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ | ​ |  | Weighted Average
​ | ​ | ​ | ​ | ​ | ​ | ​ | Remaining
​ | ​ | ​ | ​ | Weighted Average | ​ | Contractual Life (in
​ | ​ | Stock Options | ​ | Exercise Price | ​ | years)
Outstanding at December 31, 2021 |  | 1,141,675 | ​ | $ | 5.73 |  | 5.31
Outstanding at March 31, 2022 |  | 1,141,675 | ​ |  | 5.73 |  | 5.06
Options vested and exercisable at March 31, 2022 |  | 713,547 | ​ | $ | 5.73 |  | 5.06
Schedule of Stock-Based Compensation Expense | The following table summarizes stock-based compensation expense for the three months ended March 31, 2022 and 2021 (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | For the three months ended March 31, | ​
​ |  | 2022 |  | 2021 |
General and administrative | ​ | $ | 147 | ​ | $ | 324 | ​
Research and development | ​ |  | 517 | ​ |  | 672 | ​
Total stock-based compensation expense | ​ | $ | 664 | ​ | $ | 996 | ​
Summary of Warrant Activities | A summary of warrant activities for the three months ended March 31, 2022, is presented below: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ | ​ |  | Weighted Average
​ | ​ | ​ | ​ | ​ | ​ | ​ | Remaining
​ | ​ | ​ | ​ | Weighted Average | ​ | Contractual Life (in
​ | ​ | Warrants | ​ | Exercise Price | ​ | years)
Outstanding as of December 31, 2021 |  | 3,308,654 | ​ | $ | 8.02 |  | 0.73
Expired |  | (3,000,270) | ​ |  | 8.50 |  | —
Granted |  | 748,036 | ​ |  | 0.80 |  | 9.93
Outstanding as of March 31, 2022 |  | 1,056,420 | ​ | $ | 1.54 |  | 9.01
Restricted Stock Awards [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Schedules of Restricted Stock and Restricted Stock Unit Activity | The following table summarizes restricted stock award activities for the three months ended March 31, 2022: ​
​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | Weighted Average
​ | ​ | ​ | ​ | Grant Date Fair
​ | ​ | Number of Shares | ​ | Value
Nonvested at December 31, 2021 |  | 280,983 | ​ | $ | 4.05
Nonvested at March 31, 2022 |  | 280,983 | ​ | $ | 4.05
Restricted Stock Units [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Schedules of Restricted Stock and Restricted Stock Unit Activity | Certain employees and consultants have been awarded restricted stock units with time-based vesting. The following table summarizes restricted stock units’ activities for the three months ended March 31, 2022: ​
​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | Weighted Average
​ | ​ | ​ | ​ | Grant Date Fair
​ | ​ | Number of Units | ​ | Value
Nonvested at December 31, 2021 |  | 2,335,557 | ​ | $ | 3.27
Granted |  | — | ​ |  | —
Forfeited | ​ | (146,686) | ​ | ​ | —
Vested |  | (270,500) | ​ |  | 3.51
Nonvested at March 31, 2022 |  | 1,918,371 | ​ | $ | 3.00

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