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Note 5 - Share-based Compensation (Tables)
6 Months Ended
Jun. 30, 2021
Notes Tables  
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

Risk-Free interest rate

  0.13% - 0.55% 

Expected dividend yield

  

—%

 

Expected stock price volatility

  54.52% - 56.07% 

Expected life of options (in years)

  2.00 - 6.25 
Share-based Payment Arrangement, Option, Activity [Table Text Block]
          

Weighted-Average

     
      

Weighted-Average

  

Remaining Contractual

  

Aggregate Intrinsic

 
  

Shares

  

Exercise Price

  

Term (Years)

  

Value

 

Outstanding at December 31, 2020

  4,638,390  $2.44   5.64  $13,701,610 

Granted (1)

  745,825   5.25         

Exercised

  (585,000)  1.68         

Expired

              

Canceled

              

Outstanding at June 30, 2021

  4,799,215  $2.97   6.37  $5,965,132 
                 

Exercisable at June 30, 2021

  3,491,141  $2.38   5.53  $5,472,602 
Share-based Payment Arrangement, Activity [Table Text Block]
  

Three Months Ended June 30,

  

Six Months Ended June 30,

 
  

2021

  

2020

  

2021

  

2020

 

General and administrative

 $401,133  $390,701  $778,185  $770,953 

Research and development

  44,987   45,912   89,006   92,599 

Total

 $446,120  $436,613  $867,191  $863,552