Note 12 - Stock Based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

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
Total additional shares		374,782

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
General and administrative	$	3,401,653	$	137,631	$	3,626,329	$	306,424
Research and development		1,917,143		41,419		1,968,300		87,765
Total stock compensation expense	$	5,318,796	$	179,050	$	5,594,629	$	394,189

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

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

	Period ended June 30,
	2019			2018
Risk free interest rate		2.16%-2.20	%		2.47%-2.71	%
Expected term		5.00-5.94 years			5.24-5.57 years
Dividend yield		-			-
Expected volatility		107%-126%			109%-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, 2019		783,383	$	12.14		-	$	-
Granted		3,565,000		1.51		-		3,667,300
Forfeited		-		-		-		-
Expired		-		-		-		-
Outstanding as of June 30, 2019		4,348,383		3.43		9.54	$	3,806,650
Exercisable as of June 30, 2019		2,876,409		4.14		9.56	$	2,841,125
Vested and expected to vest		4,348,383	$	3.43		9.54	$	3,806,650