Stock-based compensation (Tables)

12 Months Ended

Dec. 31, 2018

A summary of option transactions for all of the Company’s stock options during the years ended December 31, 2018 and 2017 follows:

	Number of Stock Options			Weighted Average Exercise Price
Outstanding at January 1, 2017		900,139		$	5.11
Granted		101,250			1.46
Exercised		-			-
Expired/forfeited		(135,667	)		4.78
Outstanding at December 31, 2017		865,722			4.74
Granted		3,770,877			1.48
Exercised		-			-
Expired/forfeited		(293,834	)		2.80
Outstanding at December 31, 2018		4,342,765		$	2.02
Exercisable at December 31, 2018		948,297		$	3.78
Options expected to vest at December 31, 2018		3,394,468		$	1.53

Stock Options Outstanding and Exercisable

The outstanding options at December 31, 2018, have a range of exercise prices and associated weighted remaining contractual life and weighted average exercise price, as follows:

Options Range of Exercise Prices		Outstanding Number of Shares		Weighted Average Remaining Contractual Life (years)		Weighted Average Exercise Price		Exercisable Number of Shares		Exercisable Weighted Avg. Exercise Price
$	1.11 - $5.00		3,983,127		9.06	$	1.52		588,758	$	1.49
$	5.01 - $10.00		350,000		3.25		6.21		350,000		6.21
$	10.01 - $181.00		9,638		2.93		56.65		9,538		56.35
Total			4,342,765		8.58	$	2.02		948,296	$	3.78

Fair Value of Each Option Award Granted

The fair value of each option award granted during the period is estimated on the date of grant using the Black-Scholes option valuation model and assumptions as noted in the following table:

	Years Ended December 31,
	2018	2017
Risk-free interest rate	2.56-2.89%	1.98 – 2.17%
Volatility	52%-55%	46%-48%
Expected dividend yield	0%	0%
Expected life	6.0 years	5.5 years
Estimated forfeiture rate	0%	0%

Unvested Stock Option Activity

The following table summarizes the Company’s unvested stock option activity:

	Options			Weighted Average Grant Date Fair Value
Unvested balance as of Decembr 31, 2017		322,817		$	0.65
Granted		3,770,877			0.80
Vested		(488,407	)		0.63
Forfeited/expired		(210,819	)		0.51
Unvested balance at December 31, 2018		3,394,468		$	0.82