| Share-based Compensation Arrangements |
The following table summarizes stock-based compensation expense: | | | | | | | | | | | | | Years Ended December 31, | | | | 2019 | | 2018 | | | | | | Stock options | $ | 1,542,644 | | | $ | 1,059,582 | | | Restricted stock | 437,354 | | | — | | | Total stock-based compensation expense | $ | 1,979,998 | | | $ | 1,059,582 | |
The following table summarizes stock option activity: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Number of Options | | Weighted
Average
Exercise Price
per Option | | Weighted
Average Grant
Date Fair Value
per Option | | Weighted
Average
Remaining Contractual Life (Years) | | Balance December 31, 2017 | | 3,851,371 | | | $ | 3.11 | | | | | | | | Granted | | 340,000 | | | 1.18 | | | 0.54 | | | | | Exercised | | (52,500) | | | 1.24 | | | | | | | | | Forfeited | | — | | | — | | | | | | | Expired | | (271,250) | | | 3.22 | | | | | | | | | Balance December 31, 2018 | | 3,867,621 | | | 4.05 | | | | | | | | Granted | | 2,450,000 | | | 0.96 | | | 0.51 | | | | | Exercised | | (736,552) | | | 0.72 | | | | | | | | | Forfeited | | (907,500) | | | 4.49 | | | | | | | Expired | | (948,569) | | | 5.01 | | | | | | | | | Balance December 31, 2019 | | 3,725,000 | | | $ | 2.32 | | | | | | | | | | | | | | | | | Number of options exercisable at December 31, 2019 | | 3,069,000 | | | $ | 2.35 | | | | | 5.4 |
The following table summarizes restricted stock activity: | | | | | | | | | | | | | | | | | Number of Unvested Shares | | Weighted Average Grant Date Fair Value per Share | | Balance December 31, 2018 | | — | | | $ | — | | | Granted | | 1,805,222 | | | 2.57 | | | Vested | | (36,496) | | | 2.74 | | | Forfeited | | — | | | — | | | Balance December 31, 2019 | | 1,768,726 | | | $ | 2.57 | |
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