Note 14 - Stock Based Compensation (Tables)

12 Months Ended

Dec. 31, 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]

	Year Ended December 31,
	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	4.5-5.0 years
Common stock price	$	1.36
Dividend yield		-
Expected volatility		121% - 123	%

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			$
Granted		3,140,000		1.79
Exercised		(225,000)		2.40				297,250
Forfeited		(155,947)		3.31
Outstanding as of December 31, 2020		7,067,436		2.74		8.60	$	0
Exercisable as of December 31, 2020		4,714,429		3.16		8.26	$	0
Vested and expected to vest		7,067,436		2.74		8.60	$	0

Share-based Payment Arrangement, Option [Member]

Notes Tables

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

	Year Ended December 31,
	2020		2019
General and administrative	$	2,120,807	$	4,656,964
Research and development		898,602		2,445,154
Total stock compensation expense	$	3,019,409	$	7,102,118

	Year Ended December 31, 2019
General and administrative	$	1,074,183
Research and development		667,736
Total stock compensation expense	$	1,741,919