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Stockholders' Equity (Tables) | 9 Months Ended
--- | ---
Sep. 30, 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 nine months ended September 30, 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 September 30, 2022 |  | 1,141,675 | ​ |  | 5.73 |  | 4.56
Options vested and exercisable at September 30, 2022 |  | 713,547 | ​ | $ | 5.73 |  | 4.56
Schedule of Stock-Based Compensation Expense | The following table summarizes stock-based compensation expense for the three and nine months ended September 30, 2022 and 2021 (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | For the three months ended September 30, | ​ | For the nine months ended September 30, | ​
​ |  | 2022 |  | 2021 |  | 2022 |  | 2021 |
General and administrative | ​ | $ | 194 | ​ | $ | 229 | ​ | $ | 549 | ​ | $ | 793 | ​
Research and development | ​ |  | 302 | ​ |  | 655 | ​ |  | 1,261 | ​ |  | 1,634 | ​
Total stock-based compensation expense | ​ | $ | 496 | ​ | $ | 884 | ​ | $ | 1,810 | ​ | $ | 2,427 | ​
Summary of Warrant Activities | A summary of warrant activities for the nine months ended September 30, 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 |  | (3,003,770) | ​ |  | 8.50 |  | —
Granted |  | 748,036 | ​ |  | 0.80 |  | 9.43
Outstanding as of September 30, 2022 |  | 1,052,920 | ​ | $ | 1.52 |  | 8.54
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 nine months ended September 30, 2022: ​
​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | Weighted Average
​ | ​ | ​ | ​ | Grant Date Fair
​ | ​ | Number of Shares | ​ | Value
Nonvested at December 31, 2021 |  | 280,983 | ​ | $ | 4.05
Granted |  | 358,320 | ​ |  | 0.70
Vested | ​ | (129,058) | ​ | ​ | 4.89
Nonvested at September 30, 2022 |  | 510,245 | ​ | $ | 1.48
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 nine months ended September 30, 2022: ​
​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | Weighted Average
​ | ​ | ​ | ​ | Grant Date Fair
​ | ​ | Number of Units | ​ | Value
Nonvested at December 31, 2021 |  | 2,335,557 | ​ | $ | 3.27
Granted |  | 1,249,397 | ​ |  | 0.82
Forfeited | ​ | (395,935) | ​ | ​ | 2.76
Vested |  | (720,019) | ​ |  | 2.93
Nonvested at September 30, 2022 |  | 2,469,000 | ​ | $ | 2.02

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