Preferred Stock, Common Stock and Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2021

Equity [Abstract]

Summary of Stock Option Activity

A summary of the Company’s stock option activity under the 2013 Plan is as follows:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding at December 31, 2020		4,077,259		$	1.70		8.09	$	5,134,768
Granted		1,682,000		$	2.42		9.13	—
Exercised		(67,426	)	$	0.67		7.39	$	43,715
Expired/Forfeited/Exchanged		(678,374	)	$	2.85		6.54	$	3,923
Outstanding at December 31, 2021		5,013,459		$	1.80		7.85	—
Vested and expected to vest at December 31, 2021		5,024,473		$	1.80		7.85	—
Exercisable at December 31, 2021		2,580,048		$	1.83		7.27	—

Summary of Estimated Fair Value of Stock Option Award

The estimated fair value of each stock option award granted was determined on the date of grant using the Black Scholes option-pricing valuation model with the following assumptions for option grants during the years ended December 31, 2021 and 2020:

	Year Ended December 31,
	2021	2020
Risk free interest rate	0.57% - 1.08%	0.39% - 0.96%
Expected option term	5.5 - 6.0 years	5.5 - 6.0 years
Expected volatility of common stock	103.45% - 107.53%	99.73% - 103.99%
Expected dividend yield	0.0%	0.0%

Summary of Estimated Fair Value of Shares to be Acquired under Employee Stock Purchase Plan

The estimated fair value of the shares to be acquired under the ESPP was determined on the initiation date of each six-month purchase period using the Black-Scholes option-pricing valuation model with the following assumptions for ESPP shares to be purchased during the years ended December 31, 2021 and 2020 as follows:

	Year Ended December 31,
	2021	2020
Risk free interest rate	0.13%	0.13% - 1.11%
Expected term	0.5 years	0.5 years
Expected volatility of common stock	111.98%	69.72% - 111.98%
Expected dividend yield	0.0%	0.0%

Summary of Recognized Stock-Based Compensation Expense

The Company recognized stock-based compensation expense to employees and directors in its research and development and its general and administrative functions during the years ended December 31, 2021 and 2020 as follows:

	Year Ended December 31,
	2021	2020
Research and development	$          101,754	$	316,892
Selling, general and administrative	1,777,200		1,311,666
Total stock-based compensation expense	$      1,878,954	$	1,628,558

Summary of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consists of the following at December 31, 2021 and 2020:

	December 31,
	2021		2020
Stock options issued and outstanding		5,013,459		4,077,259
Authorized for future option grants		1,463,685		1,402,433
Warrants to purchase common stock		1,679,673		1,841,879
Authorized for employee stock purchase plan		344,574		244,574
Total common stock reserved for future issuance		8,501,391		7,566,145