Stockholders' equity (Tables)

6 Months Ended

12 Months Ended

Jun. 30, 2019

Dec. 31, 2018

Stockholders' Equity Note [Abstract]

Schedule of Company Recognized Stock-Based Compensation Expense

For the three and six months ended June 30, 2019 and 2018, the Company recognized stock-based compensation expense as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Cost of services	$	524	$	1,341	$	562	$	3,731
Research and development		18,333		61,080		35,460		130,551
General and administrative		61,365		140,158		137,378		292,340
Sales and marketing		5,749		11,311		10,604		25,458
	$	85,971	$	213,890	$	184,004	$	452,080

For the years ended December 31, 2018 and 2017, the Company recognized stock compensation expense as follows:

	Year Ended December 31,
	2018		2017
Cost of services	$	964	$	13,776
Research and development		241,122		237,103
General and administrative		574,244		603,787
Sales and marketing		45,951		56,732
	$	862,281	$	911,398

Summary of Status of Options Granted

A summary of the status of options granted is presented below as of and for the years ended December 31, 2018 and 2017:

	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value
Outstanding at January 1, 2017		119,106		$	44.00		8.6	$	663,298
Granted		58,324		$	17.58
Exercised		(1,167	)	$	7.01			$	11,256
Forfeited		(24,538	)	$	36.31
Expired		(12,330	)	$	83.49
Outstanding at December 31, 2017		139,395		$	31.16		8.3	$	37,339
Granted		95,800		$	3.84
Exercised		—			—
Forfeited		(18,812	)	$	11.98
Expired		(4,824	)	$	56.12
Outstanding at December 31, 2018		211,559		$	20.58		7.6	$	522
Vested and expected to vest		211,559		$	20.58		7.6	$	522
Exercisable at December 31, 2018		10,445		$	1.25		5.3	$	522

Schedule of Fair Value of Option Grant Estimated Using Black-Scholes Option Pricing Model

The fair value of each option grant was estimated at the date of grant using the Black-Scholes option pricing model based on the assumptions below:

	Year Ended December 31,
	2018		2017
Annual dividend		—		—
Expected life (in years)	5.25 - 6.25		5.25 - 6.25
Risk free interest rate	2.5 - 2.9%		1.8 - 2.3%
Expected volatility	46.0 - 49.6%		44.2 - 53.0%

Summary of Status of Restricted Stock Unit Granted

A summary of the status of restricted stock units granted is presented below as of and for the years ended December 31, 2018 and 2017:

	Number of Options			Weighted- Average Grant Date Fair Value
Unvested at January 1, 2017		750		$	42.50
Granted		11,175		$	6.93
Vested		(6,025	)	$	8.01
Forfeited		—			—
Unvested at December 31, 2017		5,900		$	31.16
Granted		—			—
Vested		(5,650	)	$	8.93
Forfeited		—			—
Unvested at December 31, 2018		250		$	42.50

Schedule of Warrants to Purchase Shares of Common Stock

At June 30, 2019 and December 31, 2018, the following warrants to purchase shares of common stock were outstanding:

				Outstanding at
Issuance	Exercise Price		Expiration	June 30, 2019		December 31, 2018
November 2009	$	197.75	November 2019		270		270
January 2010	$	197.75	January 2020		270		270
March 2010	$	197.75	March 2020		55		55
November 2011	$	197.75	November 2021		212		212
December 2011	$	197.75	December 2021		27		27
March 2012	$	2,747.50	March 2019		—		165
February 2015	$	165.00	February 2025		9,001		9,001
May 2015	$	165.00	May 2020		138,310		138,310
May 2016	$	32.81	May 2021		189,577		189,577
June 2016	$	32.81	May 2021		82,035		82,035
June 2017	$	19.50	June 2022		18,754		18,754
July 2017	$	17.25	July 2022		6,350		6,350
July 2017	$	12.50	July 2022		50,000		50,000
July 2017	$	10.63	July 2022		1,000,003		1,000,003
February 2018	$	4.06	February 2023		184,615		184,615
February 2018	$	3.25	February 2023		1,846,153		1,846,153
					3,525,632		3,525,797

At December 31, 2018 and 2017, the following warrants to purchase shares of common stock were outstanding:

				Outstanding at December 31,
Issuance	Exercise Price		Expiration	2018 (1)		2017 (1)
March 2008	$	19,763.50	March 2018		—		2
November 2009	$	197.75	November 2019		270		270
January 2010	$	197.75	January 2020		270		270
March 2010	$	197.75	March 2020		55		55
November 2011	$	197.75	November 2021		212		212
December 2011	$	197.75	December 2021		27		27
March 2012	$	2,747.50	March 2019		165		165
February 2015	$	165.00	February 2025		9,001		9,001
May 2015	$	165.00	May 2020		138,310		138,310
May 2016	$	32.81	May 2021		189,577		189,577
June 2016	$	32.81	May 2021		82,035		82,035
June 2017	$	19.50	June 2022		18,754		18,754
July 2017	$	17.25	July 2022		6,350		6,350
July 2017	$	12.50	July 2022		50,000		50,000
July 2017	$	10.625	July 2022		1,000,003		1,000,003
February 2018	$	4.06	February 2023		184,615		—
February 2018	$	3.25	February 2023		1,846,153		—
					3,525,797		1,495,031