Note 6 - Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Notes Tables

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Research and development	$	18,811	$	19,838	$	111,378	$	136,236
General and administrative		145,581		259,635		531,574		448,061
Total stock-based compensation expense	$	164,392	$	279,473	$	642,952	$	584,297

Share-based Payment Arrangement, Option, 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, 2021		2,240,204		$	8.28
Granted		1,732,515			0.91
Forfeited		(172,904	)		1.76
Outstanding at September 30, 2021		3,799,815		$	5.22		8.79	$	33,791
Exercisable at September 30, 2021		1,839,079		$	9.85		8.17	$	30,113
Vested and expected to vest at September 30, 2021		3,542,971		$	5.51		8.74	$	33,791

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

	2021			2020
Expected term (in years)		10			7.75
Risk-free interest rate		1.5	%		0.9	%
Expected volatility		123.8	%		119.7	%
Dividend yield		—	%		—	%

Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]

	Number of shares		Weighted-average grant date fair value
Unvested balance at January 1, 2021		153,000	$	0.65
Granted		138,800	$	0.72
Unvested balance at September 30, 2021		291,800	$	0.69