9.	Stock-Based Compensation

Stock Option Plans

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:

	2018			2017			2016
Weighted average risk-free interest rates		2.79	%		2.40	%		2.26	%
Expected dividend yield		0.0	%		0.0	%		0.0	%
Expected life of option (in years)		7.0			7.0			7.0
Expected volatility		71.34	%		89.73	%		88.72	%

Stock-based compensation expense related to our stock option plans was

$155,304,

$57,224,

and

$54,805

during the years ended

December 31, 2018,

2017

and

2016,

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, 2018,

stock option expense was allocated as follows:

	2018		2017		2016
General and administrative expense	$	113,306	$	31,271	$	31,191
Research and development expense		41,998		25,953		23,614
Total stock option expense	$	155,304	$	57,224	$	54,805

As of

December 31, 2018,

there was

$211,234

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

2.2

years.

Additional information concerning our stock options for the years ended

December 31, 2018,

2017

and

2016

is as follows:

	2018		2017		2016
Weighted average fair value of options granted	$	0.02	$	0.04	$	0.05
Intrinsic value of options exercised		-		-		-
Total fair value of options vested		153,838		58,337		54,757

Other Non-E

loyee Stock-Based C

ompensation

During

2018,

we issued an aggregate of

17,500,000

shares of our common stock pursuant to certain consulting and investment banking agreements. We assigned an aggregate value to these shares of

$513,500,

$314,419

of which was expensed during

2018.

The remaining

$199,081

is recorded as a prepaid expense as of

December 31, 2018

and will be recognized during

2019

over the terms of the related agreements. During

2016,

we recorded general and administrative expense of

$912,862

related to modifications made to certain stock purchase warrants.