Note 9 - Stock-based Compensation

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Text Block]

9 .	Stock-Based Compensation

Stock Option Plan

We use the Black-Scholes model for determining the grant date fair value of our stock option grants. This model utilizes certain information, such as the interest rate on a risk-free security with a term generally equivalent to the expected life of the option being valued and requires certain other assumptions, such as the expected amount of time an option will be outstanding until it is exercised or expired, to calculate the fair value of stock options granted. The significant assumptions we used in our fair value calculations were as follows:

	201 7			201 6			20 15
Weighted average risk-free interest rates		2.40	%		2.26	%		1.99	%
Expected dividend yield		0.0	%		0.0	%		0.0	%
Expected life of option (yrs)	7.0			7.0			7.0
Expected volatility		89.73	%		88.72	%		91.43	%

Stock-based compensation expense related to

our stock option plans was

$57,224,

$54,805,

and

$67,905

during the years ended

December 31, 2017,

2016

and

2015,

respectively. Stock option expense is allocated to research and development expense or to general and administrative expense based on the nature of the services provided by the related individuals. For the

three

years ended

December 31, 2017,

stock option expense was allocated as follows:

	201 7		201 6		20 15
General and administrative expense	$	31,271	$	31,191	$	45,822
Research and development expense		25,953		23,614		22,083
Total stock option expense	$	57,224	$	54,805	$	67,905

As of

December 31,

201

there was

$218,280

of unrecognized compensation expense related to stock-based compensation arrangements pursuant to our stock option plans. The unrecognized compensation expense is expected to be recognized over a weighted average remaining period of

2.6

years.

Additional information concerning our stock options for t

he years ended

December 31, 2017,

2016

and

2015

is as follows:

	201 7		201 6		201 5
Weighted average fair value of options granted	$	0.04	$	0.05	$	0.09
Intrinsic value of options exercised		-		-		-
Total fair value of options vested		58,337		54,757		66,622

Other

Non-E

loyee Stock-Based C

ompensation

We recorded

general and administrative expense of $-

$912,862

and $-

- during the years ended

December 31, 2017,

2016

and

2015,

respectively, related to modifications made to certain stock purchase warrants.