10. Commitments and Contingencies We enter into arrangements to purchase inventory requiring minimum purchase commitments in the ordinary course of business. We purchase all of our needles from Kawasumi under an agreement which expires in February 2014 and includes provision requiring us to purchase certain annual minimum quantities of needles. In January 2007, we entered into a long-term supply agreement with Membrana, pursuant to which Membrana has agreed to supply, on an exclusive basis, capillary membranes for use in the filters used with the System One for ten years. In exchange for Membrana s agreement to pricing reductions based on volumes ordered, we have agreed to purchase a base amount of membranes per year from Membrana. The agreement may be terminated by either party upon a material breach, generally following a 60-day cure period, or upon the insolvency of the other party. We maintain our corporate headquarters in a leased building located in Lawrence, Massachusetts and maintain our manufacturing operations in Mexico, Germany, and Italy. Our lease agreement at our headquarters expires in July 2012 and we have elected not to renew. Our leased manufacturing facilities are subject to lease agreements with termination dates beginning in late 2012. Our lease agreements contain certain provisions that require us to pay executory costs such as real estate taxes, operating expenses and common utilities. The total amount of rental payments due over the lease term is being charged to rent expense on the straight-line method over the term of the lease. Rent expense, net of sublease income, was $1.8 million during 2011 and $1.7 million during both 2010 and 2009. The lease agreement for our headquarters included a tenant improvement allowance paid by the landlord of $0.6 million, which has been recorded as both a leasehold improvement and a deferred rent obligation. All of our leases are accounted for as operating leases. In June 2011, we entered into a new lease agreement with 350 Riverwalk LLC for our new corpo