7. Commitments and Contingencies Lease Commitments The Company's operating lease obligations primarily consist of leased office, laboratory, and manufacturing space under a non-cancelable operating lease that expires in November 2019. The lease agreement includes a renewal provision allowing the Company to extend this lease for an additional period of three years. In addition to the minimum future lease commitments presented below, the lease requires the Company to pay property taxes, insurance, maintenance, and repair costs. The lease includes a rent holiday concession and escalation clauses for increased rent over the lease term. Rent expense is recognized using the straight-line method over the term of the lease. The Company records deferred rent calculated as the difference between rent expense and the cash rental payments. To date, deferred rent has been insignificant. In March 2016, the Company entered into an additional non-cancelable operating lease for warehouse and storage space that expires in November 2019. Rent expense was $506,000 and $259,000 for the three months ended September 30, 2017 and 2016, and $1,519,000 and $757,000 for the nine months ended September 30, 2017 and 2016, respectively. Aggregate future minimum lease payments as of September 30, 2017, are as follows (in thousands): Year ending December 31, Future Minimum Lease Payments 2017 $ 507 2018 2,033 2019 1,915 Total minimum lease payments $ 4,455 ? ? ? ? ? ? ? ? ? ? Purchase Obligations Purchase obligations consist of agreements to purchase goods and services entered into in the ordinary course of business. The Company had non-cancellable commitments to suppliers for purchases totaling $1,688,000 and $3,542,000 as of September 30, 2017 and December 31, 2016, respectively. Indemnification In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and may provide for indemnification of the counterparty. The Company's exposure under these agreements is unkno