Patent ID: 8801700

Claim:
An osmotic delivery system for delivering an active agent formulation to a fluid environment, comprising: a reservoir comprising an inner wall and a lumen, wherein the lumen contains the active agent formulation and an osmotic agent formulation; and a piston assembly positioned in the lumen to isolate the active agent formulation from the osmotic agent formulation, the piston assembly comprising a columnar body and one or more O-rings, wherein (i) the columnar body has a core made of a first material that is an incompressible material, the columnar body further comprising one or more concentric grooves, wherein the incompressible material is selected from the group consisting of an ultra high molecular weight polyethylene and a polyaryletherketone, and the incompressible material produces volatile leachates of less than 1.4 μg/mL when exposed to benzyl benzoate at 40° C. for at least 45 days, and (ii) each groove retains one of the one or more O-rings and each of the one or more O-rings are made of a second material that is an elastomeric material, wherein each O-ring engages and maintains a seal against the inner wall of the reservoir.