7. Debt Instruments

Senior Notes Payable and Warrants

On April 27, 2011, we entered into a senior note payable agreement with Venture Lending & Leasing VI, Inc. (the "Lender"). The initial loan commitment of $1,500,000 was funded in two tranches: $1,000,000 in April 2011 and $500,000 in October 2011. In May 2012, the Lender funded an additional $3,500,000 under an amendment to the 2011 agreement. The aggregate of $5,000,000 in funded loans is referred to as the "Senior Note Payable". 

The Senior Note Payable was interest-only for the first six months, after which it converted into a fully-amortizing 30-month term note. The Senior Note Payable was secured by substantially all of our assets, including accounts receivable, inventories, property and equipment, and intangible assets, including intellectual property.

Under the terms of the 2011 agreement and 2012 amendment thereto, the Lender received warrants to purchase shares of our preferred stock. Under the 2011 agreement, the Lender received warrants to purchase 128,570 shares of our Series A convertible preferred stock. 

In connection with the 2012 amendment, the Lender received additional warrants to purchase shares of Series B convertible preferred stock. 

On January 15, 2014, upon the closing of the Merger and the private placement financing discussed in Note 3, The Merger, Offering and Related Transactions, the Senior Notes Payable were settled with proceeds from the Transaction, and the warrants to purchase preferred stock issued to the Lender were exchanged for warrants to purchase common stock, which warrants remain outstanding.

As of March 31, 2014 and December 31, 2013, the outstanding principal of the loan amounted to $0 and $2,344,302 respectively, and the Company recorded interest expense of $421,793 and $631,098, respectively, for the periods then ended. 

2013 Convertible Bridge Notes

In November 2013, in anticipation of the Merger and related financing completed in January and February 2014, we completed a private placement to accredited investors of $5,000,000 of its senior subordinated secured convertible notes (the "2013 Bridge Notes"). The 2013 Bridge Notes bore interest at 10% per annum and were payable on July 15, 2014, subject to earlier conversion as described below. Interest on the 2013 Bridge Notes was to be payable at maturity, provided that upon conversion of the 2013 Bridge Notes accrued interest was forgiven.

Similar to the accounting for the 2012 Bridge Notes, we determined that the 2013 Bridge Notes should be recorded at fair market value at inception and remeasured at each subsequent reporting period. The 2013 Bridge Notes were secured by a second priority security interest on all of our assets, subject to certain limited exceptions. This security interest terminated upon conversion of the 2013 Bridge Notes in connection with the Merger and related private placement financing.

On January 15, 2014, upon the closing of the Merger and the private placement financing discussed in Note 3, The Merger, Offering and Related Transactions, the outstanding principal amount and accrued interest of the 2013 Bridge Notes was converted into Units at a conversion price of $1.00 per Unit. Also, the investors received an additional warrant to purchase a number of shares of Company common stock equal to 50% of the number of shares of Company common stock contained in the Units into which the Bridge Notes were converted (i.e. 2,500,000 shares in the aggregate), at an exercise price of $1.00 per share, for a term of three years (the "Bridge Warrants").

As of March 31, 2014 and December 31, 2013, the outstanding principal of the notes amounted to $0 and $5,062,417 including accrued interest of $62,417, respectively.

Other Notes Payable

We also financed certain leasehold improvements to our Richmond, California facility. As of March 31, 2014 and December 31, 2013, the outstanding principal on the loan was $134,626 and $144,041, respectively. Interest expense for each three month period then ending was approximately $2,466 and $2,629, respectively.