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Stock-Based Compensation (Tables)
12 Months Ended
Dec. 31, 2021
Stock-Based Compensation  
Summary of stock option activity under the Equity Plans

Weighted

    

    

Average

    

Weighted

    

Aggregate

 

Exercise Price

 

Average Remaining

 

Intrinsic

Options

 

Per Share

Life in Years

Value

Outstanding at December 31, 2019

4,024,566

$

7.48

7.98

$

2

Granted

 

2,662,500

$

2.10

 

  

 

  

Exercised

 

(32,778)

$

1.53

 

Forfeited

(260,435)

$

6.95

Outstanding at December 31, 2020

 

6,393,853

$

5.29

 

7.96

$

1,961

Granted

 

2,482,650

$

2.19

 

  

 

  

Exercised

 

(2,292)

$

1.55

 

Forfeited

(348,593)

$

3.17

Outstanding at December 31, 2021

8,525,618

$

4.48

7.58

$

7,673

Options exercisable at December 31, 2021

 

5,421,641

$

5.83

 

6.89

$

4,074

Options vested and expected to vest at December 31, 2021

 

8,525,618

$

4.48

 

7.58

$

7,673

Schedule of assumptions used to determine grant-date fair value of stock options

The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and directors during the years ended December 31, 2021 and 2020 were as follows, presented on a weighted average basis:

Year Ended December 31, 

    

2021

    

2020

Expected volatility

 

67.64

%

66.94

%

Weighted average risk-free interest rate

 

0.82

%

0.66

%

Expected dividend yield

0.00

%

0.00

%

Expected term (in years)

6.82

6.85

Summary of RSU activity under the 2016 Plan

 

Weighted

    

Number of

    

Average

 

Shares

 

Fair Value

Outstanding at December 31, 2019

 

90,500

$

1.76

Awarded

753,106

$

1.49

Settled in cash

(90,500)

$

1.76

Outstanding at December 31, 2020

753,106

$

1.52

Awarded

 

275,000

$

2.57

Settled in cash

 

(92,500)

$

1.97

Outstanding at December 31, 2021

 

935,606

$

1.76

Schedule of recognized stock-based compensation expense related to the issuance of stock option awards and RSUs to employees and non-employees in the condensed consolidated statements of operations

Year Ended

December 31, 

    

2021

    

2020

Research and development

 

$

1,641

$

1,172

General and administrative

 

2,045

 

1,604

Total

$

3,686

$

2,776