Note 10 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Notes Tables

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]

	Year ended December 31,
	2018		2017
Research and development	$	62,161	$	674,643
General and administrative		1,159,430		716,425
Total stock-based compensation expense	$	1,221,591	$	1,391,068

Share-based Compensation, Stock Options, 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, 2017		147,214		$	121.37
Granted		23,345			36.92
Expired		(98	)		225.00
Balance at January 1, 2018		170,461		$	109.74		7.13	$	4,746
Granted		44,005			15.37
Forfeited		(10,583	)		131.25
Expired		(147	)		256.50
Outstanding at December 31, 2018		203,736		$	88.14		6.70	$	143
Exercisable at December 31, 2018		167,585		$	101.69		6.25	$	143
Vested and expected to vest at December 31, 2018		203,736		$	88.14		6.70	$	143

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

	2018			2017
Expected term (in years)	5.27	—	5.66	5.27	—	6.00
Risk-free interest rate	2.3%	—	2.8%	1.8%	—	2.4%
Expected volatility	113.6%	—	115.0%	109.8%	—	136.7%
Dividend yield	—	—	—	—	—	—