Stockholders' equity (Tables)

3 Months Ended

Mar. 31, 2017

Stockholders' Equity Note [Abstract]

Warrant and option activity

	For the three months ended
	March 31,
	2017			2016
Beginning balance outstanding		39,818,347			26,397,410
Warrants issued during the period:
Expired during the period		(726,416	)		(546,667	)
Exercised during the period		-			(12,270,853	)
In connection with tender offer exercise		-			26,479,217
Ending balance outstanding		39,091,931			40,059,107

	For the three months ended
	March 31,
	2017			2016
Beginning balance outstanding		26,865,017			10,337,113
Options issued during the period		4,698,759			6,836,016
Options expired during the period		(716,830	)		(85,000	)
Ending balance outstanding		30,846,946			17,088,129

Options and warrants outstanding

Shares Issuable		Weighted Average Exercise Price		Expiration Fiscal Period
	652,516		7.85	2nd Qtr, 2017
	536,500		1.14	3rd Qtr, 2017
	1,162,088		6.45	4th Qtr, 2017
	10,000		6.60	1st Qtr, 2018
	755,000		0.26	4th Qtr, 2018
	36,973,317		0.31	1st Qtr, 2019
	1,850,007		0.44	2nd Qtr, 2019
	1,309,002		0.92	3rd Qtr, 2019
	2,603,000		1.15	4th Qtr, 2019
	8,273,172		0.15	1st Qtr, 2020
	1,475,789		0.18	4th Qtr, 2020
	3,288,713		0.12	1st Qtr, 2021
	1,427,605		0.09	2nd Qtr, 2021
	1,189,668		0.06	3rd Qtr, 2021
	4,698,759		0.02	4th Qtr, 2021
	2,813,284		0.02	4th Qtr, 2021
	133,334		7.05	4th Qtr, 2022
	68,053,402		0.49

Stock based compensation assumptions used

	For the three months ended
	March 31,
	2017			2016
Expected life (in years)	2.50 years			2.874 years
Weighted average volatility		202.30	%		108.81	%
Forfeiture rate		26.07	%		13.58	%
Risk-free interest rate		1.38	%		.96	%
Expected dividend rate		0.00	%		0.00	%