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Note 8 - Stock-based Compensation (Tables)
6 Months Ended
Jun. 30, 2022
Notes Tables  
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]
  

Three Months Ended

June 30,

  

Six Months Ended

June 30,

 
  

2022

  

2021

  

2022

  

2021

 

Research and development

 $58,892  $59,567  $117,785  $92,567 

General and administrative

  219,238   237,713   438,476   385,993 

Total stock-based compensation expense

 $278,130  $297,280  $556,261  $478,560 
Share-Based Payment Arrangement, Option, Activity [Table Text Block]
  

Number of

Options

  

Weighted

average

exercise price

per share

  

Weighted

average

remaining

contractual life

(in years)

  

Aggregate

intrinsic value

 

Balance at January 1, 2021

  72,454  $265.85         

Granted

  56,300   11.40         

Forfeited

  (5,612)  188.18         
Expired  (260)  1,575         

Outstanding at June 30, 2022

  122,882  $149.96   8.8  $ 

Exercisable at June 30, 2022

  60,688  $283.73   8.1  $ 

Vested and expected to vest at June 30, 2022

  122,882  $149.96   8.8  $ 
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
  

2022

  

2021

 

Expected term (in years)

  5.74   10 

Risk-free interest rate

  1.9%  1.5%

Expected volatility

  135.0%  124.5%

Dividend yield

  %  %
Share-Based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]
  

Number of

Units

  

Weighted

average

grant date fair

value

 

Balance at January 1, 2022

  5,509  $34.78 

Vested (1)

  (837)  29.87 

Outstanding at June 30, 2022

  4,672  $35.66