Note 13 - Stock Based Compensation (Tables)

9 Months Ended

Sep. 30, 2020

Notes Tables

Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]

January 1,	Number of shares
2012		2,502
2013		2,871
2014		4,128
2015		5,463
2016		7,257
2017		12,623
2018		106,076
2019		233,862
2020		365,239
Total additional shares		740,021

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Period ended September 30,
	2020		2019
Risk-free interest rate		0.28% - 0.47%		2.16% - 2.20%
Expected term	4.50-6.18 years		5.00-5.94 years
Dividend yield		-		-
Expected volatility		103% - 129%		107% - 126%

	January 13,
	2019
Risk-free interest rate		2.53	%
Expected term (in years)		4.50 - 5.00
Stock price	$	1.36
Dividend yield		-	%
Expected volatility		121.0 - 123.0	%

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

	Number of Underlying Shares		Weighted- Average Exercise Price Per Share		Weighted- Average Contractual Life Remaining in Years		Aggregate Intrinsic Value
Outstanding as of January 1, 2020		4,308,383	$	3.44		-	$	651,000
Granted		3,140,000		1.79		-		449,600
Exercised		(225,000)		2.40		-		297,250
Forfeited		(143,552)		1.87		-		272,000
Expired		-		-		-		-
Outstanding as of September 30, 2020		7,079,831		2.77		8.85	$	5,629,600
Exercisable as of September 30, 2020		4,332,821		3.34		8.42	$	3,616,727
Vested and expected to vest		7,079,831	$	2.77		8.85	$	5,629,600

Share-based Payment Arrangement, Option [Member]

Notes Tables

Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
General and administrative	$	489,853	$	510,398	$	1,675,414	$	4,136,727
Research and development		173,740		241,254		712,415		2,209,554
Total stock compensation expense	$	663,593	$	751,652	$	2,387,829	$	6,346,281

General and administrative	$	1,074,183
Research and development		667,736
Total stock compensation expense	$	1,741,919