An osmotic pump having a minimally compliant, volume-efficient piston positioned within a capsule is provided. The capsule has an interior surface, a beneficial agent, and an osmotic agent. The piston is movable with respect to an interior surface of the capsule, and defines a movable seal with the interior...http://www.google.com.au/patents/US6939556?utm_source=gb-gplus-sharePatent US6939556 - Minimally compliant, volume efficient piston for osmotic drug delivery systems
