6.    Notes Payable

Senior Secured Note Payable

The indebtedness outstanding under the Brainlab Note at December 31, 2015 was approximately $5.0 million and was to mature in April 2016. The indebtedness included approximately $740,000 of accrued interest, which had accrued at a rate of 5.5% and was payable in a single aggregate installment upon maturity.

On April 4, 2016 (the “Closing Date”), the Company and Brainlab consummated the transactions under the 2016 Purchase Agreement, as discussed below.

2016 Purchase Agreement

Under the 2016 Purchase Agreement, the Company: (i) paid to Brainlab all accrued and unpaid interest on the Brainlab Note, in the amount of approximately $740,000; (ii) amended and restated the Brainlab Note on the terms described below; (iii) entered into a patent and technology license agreement with Brainlab (the “License Agreement”) for software relating to the Company’s SmartFrame device, in consideration for the cancellation of $1.0 million of the principal amount of the Brainlab Note; (iv) issued to Brainlab, in consideration for the cancellation of approximately $1.3 million of the principal amount of the Brainlab Note, 99,310 units, with each unit consisting of: (a) one share of the Company’s common stock; (b) a warrant to purchase 0.4 share of common stock (the “2016 Series A Warrants”); and (c) a warrant to purchase 0.3 shares of common stock (the “2016 Series B Warrants”) (collectively, the “Equity Units”); and (v) entered into a Registration Rights Agreement (the “2016 Registration Rights Agreement”), pursuant to which the Company agreed to file a registration statement with the SEC covering the resale of the shares of common stock issued to Brainlab under the 2016 Purchase Agreement, as well as the shares of common stock that are issuable upon exercise of the 2016 Series A Warrants and 2016 Series B Warrants (together, the “2016 Warrants”).

The 2016 Purchase Agreement contains covenants, representations and warranties by the Company and Brainlab (including indemnification from the Company in the event of breaches of its representations and warranties), which the Company believes are customary for transactions of this type.

As a result of the foregoing, on the Closing Date, the Company recorded a debt restructuring gain of approximately $941,000 representing the difference between (a) the aggregate fair value of the License Agreement, which had no cost basis on the Company’s consolidated balance sheets, and the Equity Units, and (b) the aggregate principal amount of the Brainlab Note cancelled as consideration.

2016 Registration Rights Agreement

The 2016 Registration Rights Agreement imposed deadlines by which the Company was required to file the 2016 Registration Statement and use its best efforts to have the 2016 Registration Statement declared effective. The 2016 Registration Statement was filed, and declared effective on June 20, 2016, within the deadlines imposed by the 2016 Registration Rights Agreement. Pursuant to the 2016 Registration Rights Agreement, if the Company fails to continuously maintain the effectiveness of the 2016 Registration Statement (with certain permitted exceptions), the Company will incur certain liquidated damages in a range of 2%-10%, depending on the duration of such failure, of the approximately $1.3 million principal reduction of the Brainlab Note as described above. The 2016 Registration Rights Agreement also contains mutual indemnifications by the Company and Brainlab, which the Company believes are customary for transactions of this type.

2016 Warrants

The 2016 Series A Warrants and 2016 Series B Warrants are exercisable, in full or in part, at any time prior to the fifth anniversary of their issuance, at an exercise price of $16.23 per share (before giving effect to the Note Conversion as defined below) and $21.10 per share, respectively. The 2016 Warrants provide for certain adjustments that may be made to the exercise price and the number of shares issuable upon exercise due to future corporate events or otherwise. In the case of certain fundamental transactions affecting the Company, the holder of such 2016 Warrants, upon exercise of such warrants after such fundamental transaction, will have the right to receive, in lieu of shares of the Company’s common stock, the same amount and kind of securities, cash or property that such holder would have been entitled to receive upon the occurrence of the fundamental transaction, had the 2016 Warrants been exercised immediately prior to such fundamental transaction. The 2016 Warrants contain a “cashless exercise” feature that allows the holders to exercise the warrants without a cash payment to the Company upon the terms set forth in the respective 2016 Warrant agreements.

Amended and Restated Promissory Note

On the Closing Date and pursuant to the 2016 Purchase Agreement, the Company issued Brainlab an unregistered, amended and restated secured note (the “New Brainlab Note”), which has the same terms and conditions as the Brainlab Note, except that: (i) the principal amount of the New Brainlab Note is $2 million; (ii) interest will be paid quarterly in arrears; and (iii) the maturity date of the New Brainlab Note is December 31, 2018.

Non-Exclusive License Agreement

On the Closing Date and pursuant to the 2016 Purchase Agreement, the Company and Brainlab entered into the License Agreement, for software relating to the Company’s SmartFrame device, for use in neurosurgery. The License Agreement does not affect the Company’s ability to continue to independently develop, market and sell its own software for the SmartFrame device.

The New Brainlab Note is collateralized by a senior security interest in the assets of the Company.

2014 Junior Secured Notes Payable

In March 2014, the Company entered into securities purchase agreements for the private placement of: (i) second-priority secured non-convertible promissory notes (the “2014 Secured Notes”); and (ii) warrants to purchase 0.01 shares of the Company’s common stock for each dollar in principal amount of the 2014 Secured Notes sold by the Company. Pursuant to those securities purchase agreements, the Company sold 2014 Secured Notes in a total aggregate principal amount of $3,725,000, together with warrants to purchase up to 27,937 shares of common stock, for aggregate gross proceeds of $3,725,000, before placement agent commissions and other expenses.

The 2014 Secured Notes have a five-year term and bear interest at a rate of 12% per year, payable semi-annually, in arrears. The 2014 Secured Notes are not convertible into shares of the Company’s common stock. Following the third anniversary of the issuance date, the 2014 Secured Notes may be prepaid, without penalty or premium, provided that all principal and unpaid accrued interest under all 2014 Secured Notes is prepaid at the same time. Prior to the third anniversary of the issuance date, the Company may prepay all, but not less than all, of the principal and unpaid accrued interest under the 2014 Secured Notes at any time, subject to the Company’s payment of the additional prepayment premium stated in the notes. The 2014 Secured Notes are collateralized by a security interest in the Company’s property and assets, which security interest is junior and subordinate to the security interest that collateralizes the New Brainlab Note.

The warrants issued to the investors (the “investor warrants”) are exercisable, in full or in part, at any time prior to the fifth anniversary of the issuance date, at an original exercise price of $70.00 per share, subject to adjustment from time-to-time for stock splits or combinations, stock dividends, stock distributions, recapitalizations and other similar transactions. Assumptions used in calculating the fair value of the investor warrants using the Black-Scholes valuation model were:

Under GAAP, the Company allocated the $3,725,000 in proceeds proportionately between the 2014 Secured Notes and the investor warrants based on their relative fair values, with $413,057 being allocated to the fair value of the investor warrants, recorded as equity. The 2014 Secured Notes were recorded at the principal amount, less a discount equal to $413,057. After giving effect to the conversions discussed below under the heading “August 31, 2016 Amendments,” the unamortized discount at December 31, 2016 and 2015 was $121,985 and $301,531, respectively. This discount is being amortized to interest expense over the five-year term of the 2014 Secured Notes using the effective interest method. The carrying amount of the 2014 Secured Notes in the accompanying condensed consolidated balance sheets is also presented net of issuance costs, as discussed further below.

Non-employee directors of the Company purchased a total of $1,100,000 of the 2014 Secured Notes, either directly or through a trust. The Company’s placement agents earned cash commissions of $145,500 as well as warrants (the “placement agent warrants”) to purchase 1,818 shares of the Company’s common stock. The placement agent warrants have the same terms and conditions as the investor warrants.

The placement agent cash commissions, the $30,210 fair value of the placement agent warrants, and other offering expenses, aggregating $76,186, were recorded as deferred financing costs and are presented as reductions of the carrying amount of the 2014 Secured Notes in the accompanying consolidated balance sheets. These deferred financing costs, having an unamortized balance of $58,789 and $166,080 at December 31, 2016 and 2015, respectively, are being amortized to interest expense over the term of the 2014 Secured Notes using the effective interest method.

2010 Junior Secured Notes Payable

In November 2010, the Company issued units consisting of a junior secured note (the “2010 Secured Notes”) and one share of the Company’s common stock. An aggregate of 267,857 units were issued, and the Company received proceeds of $3,000,000 representing the aggregate principal amount of the 2010 Secured Notes. The 2010 Secured Notes mature in November 2020, accrue interest at the rate of 3.5% per year, and are collateralized by a security interest in the assets of the Company, which security interest is junior and subordinate to the security interests that collateralize the Brainlab Note and the 2014 Secured Notes. All outstanding principal and interest on the 2010 Secured Notes will be due and payable in a single payment upon maturity.

Under GAAP, the Company allocated the $3 million in proceeds from the sale of the units between the 2010 Secured Notes and the shares of common stock based on their relative fair values, with the fair value of the notes being estimated based on an assumed market interest rate for notes of similar terms and risk, and the fair value of the Company’s common stock being estimated by management using a market approach, with input from a third-party valuation specialist. The allocation of such relative fair values resulted in $2,775,300 being allocated to the value of the shares of common stock, which was recorded as equity. The 2010 Secured Notes were recorded at the principal amount of $3,000,000, less a discount equal to $2,775,300. The unamortized discount at December 31, 2016 and 2015 was $2,302,472 and $2,535,230, respectively. This discount is being amortized to interest expense over the 10-year term of the notes using the effective interest method.

Four then-serving officers of the Company purchased an aggregate of 22,068 units in the offering for $247,164. In addition, three non-employee directors of the Company also purchased an aggregate of 14,180 units in the offering for $158,816.

June 30, 2016 Amendments

On June 30, 2016, the Company entered into amendments (the “First Amendments”) with: (a) Brainlab, with respect to the New Brainlab Note; and (b) the 2014 Convertible Note Holders, one of whom is a trust for which one of the Company’s non-employee directors serves as a trustee, having an aggregate principal balance of $3 million. Pursuant to the First Amendments, the parties agreed that, in the event the Company closes a qualified public offering: (i) $500,000 of the principal balance of the New Brainlab Note, and an aggregate $1.5 million of the principal balance of the 2014 Secured Notes, plus all unpaid accrued interest on such principal amounts, would automatically convert into the security offered in the qualified public offering, based on the public offering price of that security; and (ii) the exercise price for 34,957 shares of common stock underlying warrants issued in connection with the New Brainlab Note, and 11,250 shares of common stock underlying warrants issued in connection with the 2014 Secured Notes, would be reduced to equal the greater of (x) the public offering price of the security offered in the qualified public offering, or (y) if the security offered in the qualified public offering is or includes convertible stock or common stock warrants, the highest price per whole share for which the Company’s common stock is issuable upon conversion of such convertible stock or upon exercise of such common stock warrants. These provisions created: (a) a conversion feature allowing for the principal balances described above, plus all unpaid related accrued interest, to be converted into the security offered in the public offering, and at a price that may be less than the market value per share of the Company’s common stock; and (b) down round strike price protection with respect to the warrants, both of which, under GAAP, are required to be accounted for as derivatives, the calculation and accounting for which is described in Note 8.

Execution of the First Amendments constituted a debt extinguishment under GAAP, necessitating the Company to record a debt restructuring loss of approximately $820,000, representing the aggregate difference in the fair values of the New Brainlab Note and the affected 2014 Secured Notes between (i) their respective original dates of issuance, and (ii) June 30, 2016, the execution date of the First Amendments.

August 31, 2016 Amendments

On August 31, 2016, the Company entered into second amendments (the “Second Amendments”) with the 2014 Convertible Note Holders.

Pursuant to the Second Amendments, the parties agreed that, in the event the Company closes a PIPE Transaction (as that term is defined in the Second Amendments; the “2016 PIPE”): (i) an aggregate $1.75 million of aggregate principal balance of the 2014 Convertible Note Holders’ 2014 Secured Notes (the “2014 Principal”) would automatically convert into the security offered by the Company in the 2016 PIPE, based on the offering price of that security in the 2016 PIPE (the “Note Conversion”); and (ii) the exercise price for 13,125 shares of common stock that may be purchased upon exercise of warrants issued in connection with the issuance of the 2014 Secured Notes (the “2014 Warrants”) will be reduced to equal the greater of (x) the offering price of the security offered in the 2016 PIPE, or (y) if the security offered in the 2016 PIPE is or includes convertible stock or common stock warrants, the highest price per whole share for which the Company’s common stock is issuable upon conversion of such convertible stock or upon exercise of such common stock warrants. These provisions maintained but modified: (a) the conversion feature allowing for the 2014 Principal to be converted into the security offered in the 2016 PIPE, and at a price that may be less than the market value per share of the Company’s common stock; and (b) the down round strike price protection with respect to the 2014 Warrants, both of which, under GAAP, are required to be accounted for as derivatives, the calculation and accounting for which is described in Note 8.

Execution of the Second Amendments constituted a debt extinguishment under GAAP, necessitating the Company to record a debt restructuring loss of approximately $933,000, representing the aggregate difference in the fair value of the derivatives described in the preceding paragraph between the points in time (i) immediately preceding, and (ii) immediately subsequent to, the execution of the Second Amendments.

As more fully described in Note 7, the 2016 PIPE was completed on September 2, 2016, resulting in (i) conversion of the 2014 Principal, and (ii) establishment of a fixed exercise price and elimination of the down round price protection with respect to the 2014 Warrants, in conformity with the terms set forth in the Second Amendments. Accordingly, concurrent with completion of the 2016 PIPE, derivative liabilities associated with the conversion feature of the 2014 Principal and the down round price protection for the 2014 Warrants were reduced by $1,207,813, with a corresponding amount being recorded as an increase to stockholders’ equity.

Scheduled Notes Payable Maturities

Scheduled principal payments as of December 31, 2016 with respect to notes payable are summarized as follows: