In April 2017, the Company entered into a Controlled Equity Offering Sales Agreement (the “Sales Agreement”) with Cantor Fitzgerald & Co. (“Cantor”), as sales agent, pursuant to which the Company had the right to offer and sell, from time to time, through Cantor, shares of the Company’s common stock, par value $0.001 per share, by any method deemed to be an “at the market offering” as defined in Rule 415(a)(4) under the Securities Act of 1933, as amended (the “Securities Act”), (the “ATM Offering”). In April 2017, the Company also filed a prospectus supplement (File No. 333-216977) with the SEC relating to the offer and sale of up to $20.0 million of common stock in the ATM Offering. In June 2017, the Company filed a first amendment to the prospectus supplement with the SEC to increase the amount of common stock that could be offered and sold in the ATM Offering under the Sales Agreement to $40.0 million in the aggregate, inclusive of the common stock previously sold in the ATM Offering prior to the date of the first amendment. In January 2018, the Company filed a second amendment to the prospectus supplement with the SEC to decrease the amount of common stock that could be offered and sold in the ATM Offering under the Sales Agreement to $23.0 million in the aggregate, inclusive of the common stock sold in the ATM Offering prior to the date of the second amendment. In February 2018, the Company and Cantor mutually agreed to terminate the Sales Agreement.

Prior to termination of the Sales Agreement, the Company sold 5,733,314 shares of common stock under the ATM Offering at then-market prices for total gross proceeds of approximately $21.1 million, including 0.3 million shares of common stock sold for gross proceeds of $0.6 million during the first quarter ended March 31, 2018. After $0.6 million of sales commissions and $0.2 million of other offering expenses paid by the Company in connection with the ATM Offering, the Company’s aggregate net proceeds from the ATM Offering were approximately $20.2 million. Sales commissions and offering expenses have been recorded as a reduction of proceeds received in arriving at the amounts recorded in additional paid-in capital in the accompanying consolidated balance sheets as of December 31, 2018.

In January 2018, the Company completed an underwritten public offering of 13,915,000 shares of its common stock at a price of $2.90 per share, including 1,815,000 shares sold pursuant to the exercise in full of the underwriters’ option to purchase additional shares. The Company sold its common stock through an underwriting agreement with Leerink Partners LLC and Cantor as representatives of the underwriters for the offering. The aggregate net proceeds to the Company from the offering were approximately $37.7 million, after deducting the underwriting discounts and commissions and offering expenses.

In March 2019, the Company entered into a Controlled Equity Offering Sales Agreement (“Cowen Sales Agreement”) with Cowen and Company (“Cowen”), as sales agent, pursuant to which the Company has the right to offer and sell, from time to time, through Cowen, shares of the Company’s common stock, having an aggregate offering price of up to $40.0 million, by any method deemed to be an “at the market offering” as defined in Rule 415(a)(4) under the Securities Act (the “Cowen ATM Offering”) under the Company’s shelf registration statement on Form S-3 (File No. 333-229045). Approximately $0.2 million of costs incurred in connection with the offering were capitalized as deferred offering costs in the Company’s 2019 consolidated balance sheet upon entry into this agreement.

As of December 31, 2019, no shares were sold under the Cowen ATM Offering and no shares will be sold under the Cowen ATM Offering as the Company terminated the Cowen Sales Agreement in November 2019. As a result of this termination, the Company wrote off approximately $0.1 million of the previously capitalized deferred offering costs as the Company will not utilize these costs in the sale of shares through the Cowen ATM Offering. The remaining approximately $60,000 of costs capitalized as deferred offering costs in the consolidated balance sheets related to the filing of the Form S-3 were able to be utilized for the 2019 ATM Offering discussed below.

In September 2019, the Company entered into an underwriting agreement with Cantor (the “2019 Underwriting Agreement”), relating to the issuance and sale in a public offering of 29,298,537 shares of its common stock, including 3,821,548 shares sold pursuant to the full exercise of the underwriter’s option to purchase additional shares. The price to the public in the offering was $0.65 per share and the underwriter agreed to purchase the shares from the Company pursuant to the 2019 Underwriting Agreement at a price of $0.611 per share. The net proceeds to the Company were approximately $17.7 million, after deducting the underwriting discounts and commissions and offering expenses.

The offering was made pursuant to the Company’s registration statement on Form S-3 (Registration Statement No. 333‑229045), previously filed with the Securities and Exchange Commission (“SEC”) and declared effective by the SEC on February 11, 2019, and a prospectus supplement and accompanying prospectus thereunder.

In September 2019, concurrent with the closing of the September 2019 underwritten public offering, the Company entered into a Securities Purchase Agreement (the “Securities Purchase Agreement”) with certain institutional accredited investors (the “Purchasers”), pursuant to which the Company sold to the Purchasers, in a private placement transaction, an aggregate of 5,411,687 pre-funded warrants to purchase up to an aggregate of 5,411,687 shares of our common stock (“Warrant Shares”), at a price of $0.64 per warrant (which $0.64 price relates to the pre-funded portion of the total $0.65 exercise price per share). Each pre-funded warrant has a remaining exercise price of $0.01 per share and became immediately exercisable upon issuance, subject to certain beneficial ownership limitations.

The exercise price of the pre-funded warrants will be subject to adjustment in the event of any stock dividends and splits, recapitalization, reorganization or similar transaction, as described in the pre-funded warrants. The pre-funded warrants are exercisable on a “cashless” basis in certain circumstances.

The pre-funded warrants and the Warrant Shares were not registered under the Securities Act and were offered pursuant to the exemption provided in Section 4(a)(2) under the Securities Act and Rule 506(b) promulgated thereunder. The Company agreed to file a registration statement to register the resale of the Warrant Shares within 30 days following the date of the Closing and to obtain effectiveness of such registration statement within 90 days following the Closing, subject to certain exceptions. Each Purchaser was an “accredited investor” as defined in Rule 501(a) under the Securities Act.

Cantor (the “Placement Agent”) acted as the sole placement agent in connection with the private placement of the warrants. Pursuant to a Placement Agency Agreement between us and the Placement Agent, we agreed to pay the Placement Agent a cash fee equal to 6% of the gross proceeds to us from the sale of the pre-funded warrants, and to provide reimbursement for certain out-of-pocket expenses. Upon closing, the Company received approximately $3.1 million in net proceeds from the sale of the pre-funded warrants in the private placement, which does not include proceeds that may be received upon exercise of the pre-funded warrants, after deducting the Placement Agent fee and other expenses.

In November 2019, the Company entered into a Controlled Equity Offering Sales Agreement (the “Cantor Sales Agreement”) with Cantor as sales agent, pursuant to which the Company may offer and sell, from time to time, through Cantor, shares of the Company’s common stock, par value $0.001 per share, having an aggregate offering price of up to $20.0 million, by any method deemed to be an “at the market offering” as defined by rule 415(a)(4) under the Securities Act (the “2019 ATM Offering”). The shares will be offered and sold pursuant to the Company’s shelf registration statement on Form S-3 (File No. 333-229045).

The Company is not obligated to sell any shares under the Cantor Sales Agreement. Approximately $81,000 of costs incurred in connection with the offering were capitalized as deferred offering costs in the Company’s consolidated balance sheets upon entry into this agreement in addition to the Form S-3 costs capitalized previously, as discussed in Cowen ATM Offering above, of which $45,000 are reimbursable by Cantor through reduction of commissions earned on shares sold under the Cantor Sales Agreement. The Company is not obligated to sell any shares under the Cantor Sales Agreement and will pay Cantor a commission of up to 3.0% of the aggregate gross proceeds from each sale of shares, reimburse legal fees and disbursements and provide Cantor with customary indemnification and contribution rights. The Sales Agreement may be terminated by Cantor or the Company at any time upon notice to the other party, or by Cantor at any time in certain circumstances, including the occurrence of a material and adverse change in the Company’s business or financial condition that makes it impractical or inadvisable to market the shares or to enforce contracts for the sale of the shares. There were no shares sold under the Cantor Sales Agreement through December 31, 2019. See Note 17 for further information regarding the 2019 ATM Offering.

Pursuant to the Company Amended and Restated Certificate of Incorporation, the Company is authorized to issue 200,000,000 shares of common stock at a par value of $0.001 per share.

Each share of common stock is entitled to one vote. The shares of common stock have no preemptive or conversion rights, no redemption or sinking fund provisions, no liability for further call or assessment, and are not entitled to cumulative voting rights.

Pursuant to the Company’s certificate of incorporation the Company has been authorized to issue 10,000,000 shares of preferred stock, each having a par value of $0.001. The preferred stock may be issued from time to time in one or more series with the authorization of the Company’s Board of Directors. The Board of Directors can determine voting power for each series issued, as well as designation, preferences, and relative, participating, optional or other rights and such qualifications, limitations or restrictions thereof.

The Company incurs stock-based compensation expense relating to the grants under its equity incentive plans of RSUs and stock options to employees, non-employee directors and consultants of the Company and its affiliates and through the ESPP.

The Company initially established the 2001 Stock Option Plan (the “2001 Plan”), which included incentive and nonqualified stock options and restricted stock to be granted to directors, officers, employees, consultants and others. The 2001 Plan terminated, and no further awards were granted under the 2001 Plan upon the effective date of the Company’s 2011 Equity Incentive Plan (the “2011 Plan”).

In February 2014, the number of shares reserved under the 2011 Plan was increased to 20% of the total outstanding shares of the Company calculated on a fully diluted basis. The shares reserved under the 2011 Plan were required to be kept at that percentage with each subsequent equity financing. No new equity awards may be granted under the 2011 Plan.

In May 2015, 940,112 shares were reserved for issuance under the Company’s 2014 Equity Incentive Plan (the “2014 Plan”), including 14,006 remaining shares reserved under the 2011 Plan. No shares of the Company’s stock available for issuance under the 2014 Plan as of December 31, 2019, other than those reserved for inducement awards, as outlined below. On January 1, 2020, an additional 2,323,609 shares were registered for issuance under the 2014 Plan pursuant to an evergreen provision contained in the 2014 Plan.

In May 2019, 200,000 shares were reserved for issuance under the 2014 Plan pursuant to an amendment approved by the Company’s Board of Directors pursuant to Rule 5635(c)(4) of the Nasdaq Listing Rules, to be used exclusively for the grant of awards to individuals who were not previously employees or non-employee directors of the Company, as inducement material to the individuals’ entering into employment with the Company (“Inducement Awards”). As of December 31, 2019, there were 120,000 Inducement Awards available for issuance under the 2014 Plan.

The Company’s Board of Directors determines the grant date for all awards granted under the 2014 Plan. The option exercise price of stock options and Inducement Awards granted is generally equal to the closing price of the Company’s common stock on the date of grant or on the employee’s hire date for new hire grants. All stock options granted have a ten-year term. The vesting period of stock options, Inducement Awards and RSUs is established by the Board of Directors but typically ranges between one and four years.

Amounts recognized in the accompanying consolidated statements of operations with respect to the Company’s equity incentive plans were as follows:

	Years Ended December 31,
	2019		2018
Selling, general and administrative	$	859,653	$	1,668,227
Research and development		243,804		159,450
Cost of product and product-related services revenue		53,110		60,378
	$	1,156,567	$	1,888,055

The following table summarizes stock option activity during the two-year period ended December 31, 2019:

	Number of Shares			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value
Balance at January 1, 2018		1,517,771		$	2.97		7.5	$	67,242
Granted		802,500			3.39
Exercised		(144,645	)		2.19			$	243,531
Forfeited		(66,428	)		3.24
Expired/Cancelled		(61,961	)		6.52
Balance at December 31, 2018		2,047,237		$	3.07		7.6	$	366,007
Granted		1,270,000			1.48
Exercised		(54,256	)		2.23			$	21,380
Forfeited		(161,571	)		3.29
Expired/Cancelled		(196,512	)		3.23
Balance at December 31, 2019		2,904,898		$	2.37		8.0	$	781
Vested and expected to vest at December 31, 2019		2,904,898			2.37		8.0	$	781
Exercisable at December 31, 2018		1,256,352			2.91		6.5	$	346,595
Exercisable at December 31, 2019		1,380,865			2.84		6.6	$	96

The weighted-average fair value of stock options granted was $0.97 and $2.29 for the years ended December 31, 2019 and 2018, respectively. This activity includes 80,000 Inducement Awards granted during the year ended December 31, 2019. No Inducement Awards were granted during the year ended December 31, 2018. As of December 31, 2019, total unrecognized compensation cost related to stock option awards was approximately $1,833,329, which is expected to be recognized over approximately 2.31 years.

In June 2018, in connection with the retirement of two employees, the vesting of stock options covering 46,613 shares of common stock was accelerated and the post-termination exercise period for the employees’ options was extended to a one-year period from the termination date. As a result of this modification, the Company recorded incremental stock-based compensation expense of approximately $79,400 for the year ended December 31, 2018.

The fair value of each stock option granted has been determined using the Black-Scholes option pricing model. The material factors incorporated in the Black-Scholes model in estimating the fair value of the stock options granted for the periods presented were as follows:

In preparing its Black-Scholes option-pricing model fair value calculations, the Company does not estimate a forfeiture rate to calculate stock-based compensation. The Company uses judgment in evaluating the expected volatility and expected terms utilized for the Company’s stock-based compensation calculations on a prospective basis.

The following table summarizes RSU award activity during the two-year period ended December 31, 2019:

	Number of Shares			Weighted- Average Grant Date Fair Value Per Share
Balance at January 1, 2018		26,666		$	2.78
Granted		492,051			3.63
Released		(291,010	)		3.72
Balance at December 31, 2018		227,707		$	3.30
Granted		77,500			1.93
Released		(81,462	)		3.31
Balance at December 31, 2019		223,745		$	2.91
Vested and unissued at December 31, 2019		15,942		$	3.14

The weighted-average fair value of RSUs granted was $1.93 and $3.63 for the years ended December 31, 2019 and 2018, respectively. As of December 31, 2019, total unrecognized compensation cost related to RSU awards was approximately $555,439, which is expected to be recognized over approximately 2.26 years.

Vested and unissued awards at December 31, 2019 represents RSU awards granted on August 16, 2018, January 21, 2019 and September 12, 2019 for which a portion of the awards vested on December 31, 2019, but for which issuance of awards occurred on the next business day, January 2, 2020.

In April 2015, the Company’s stockholders approved the 2014 Employee Stock Purchase Plan, which became effective in May 2015. Initially, the ESPP authorized the issuance of up to 110,820 shares of common stock pursuant to purchase rights granted to the Company’s employees or to employees of any of the Company’s designated affiliates. The number of shares of common stock reserved for issuance automatically increases on January 1 of each calendar year, from January 1, 2016 to January 1, 2024 by the least of (i) 1% of the total number of shares of the Company’s common stock outstanding on December 31 of the preceding calendar year, (ii) 195,000 shares, or (iii) a number determined by the Company’s board of directors that is less than (i) and (ii). The ESPP enables participants to contribute up to 15% of such participant’s eligible compensation during a defined period (not to exceed 27 months) to purchase common stock of the Company. The purchase price of common stock under the ESPP is the lesser of: (i) 85% of the fair market value of a share of the Company’s common stock on the first day of an offering or (ii) 85% of the fair market value of the Company’s common stock at the applicable purchase date.

Amounts recognized in the accompanying consolidated statements of operations with respect to the ESPP were as follows:

	Years Ended December 31,
	2019		2018
Selling, general and administrative	$	43,615	$	41,716
Research and development		18,454		12,556
Cost of product and product-related services revenue		4,169		4,687
	$	66,238	$	58,959

During the year ended December 31, 2019, employees entering the plan at various times throughout the year purchased the following shares at the end of each of the ESPP’s six-month purchase periods:

	June 2019				December 2019
	Number of Shares		Price per Share		Number of Shares		Price per Share
ESPP Group:
Group A		29,580	$	1.57		27,449	$	0.57
Group B		5,828		1.79		5,240		0.57
Group C		4,581		1.79		4,804		0.57
Group D		—	N/A			2,474		0.57
Total number of shares purchased		39,989				39,967

During the year ended December 31, 2018, employees entering the plan at various times throughout the year purchased the following shares at the end of each of the ESPP’s six-month purchase periods:

	June 2018				December 2018
	Number of Shares		Price per Share		Number of Shares		Price per Share
ESPP Group:
Group A		39,976	$	1.57		35,805	$	1.57
Group B		—	N/A			4,176		2.81
Total number of shares purchased		39,976				39,981

As of December 31, 2019, approximately 273,111 shares of the Company’s common stock were reserved for future issuance under the ESPP. On January 1, 2020, an additional 195,000 shares were registered for issuance pursuant to an evergreen provision contained in the ESPP.

The Company recognizes ESPP expense based on the fair value of the ESPP stock purchase rights, estimated for each six-month purchase period using the Black-Scholes option pricing model. The model requires the Company to make subjective assumptions, including expected stock price volatility, risk free rate of return and estimated life. The fair value of equity-based awards is amortized straight-line over the vesting period of the award.

The material factors incorporated in the Black-Scholes model in estimating the fair value of the ESPP awards for the periods presented were as follows:

In December 2015, the Board of Directors adopted a Stock Purchase Plan (the “Purchase Plan”) which allows directors, any individual deemed by the Board of Directors to be an officer for purposes of Section 16 of the Exchange Act, and anyone designated by the Board of Directors as eligible to participate in the Purchase Plan to purchase shares of the Company’s common stock from the Company at fair market value. The aggregate number of shares of common stock that may be issued under the Purchase Plan shall not exceed 250,000 shares of common stock, and a maximum of 7,500 shares of common stock may be purchased by any one participant on any one purchase date. The Board of Directors or an authorized committee must review and approve each individual request to purchase common stock under the Purchase Plan. Cash received from the sale of common stock by the Company to eligible participants for the year ended December 31, 2019 was $17,250, which resulted in the sale of 7,500 shares of the Company’s common stock at fair market value. Cash received from the sale of common stock by the Company to eligible participants for the year ended December 31, 2018 was $9,997 which resulted in the sale of 2,304 shares of the Company’s common stock at fair market value. As of December 31, 2019, there were 174,871 shares available for issuance under the Purchase Plan.