US Patent 7407499 Osmotic pump with self-retaining, fast-start membrane plug

An osmotic pump includes a capsule having at least one delivery port formed at a first end and a membrane plug retained in a second end of the capsule remote from the delivery port to provide a fluid-permeable barrier between an interior and an exterior of the capsule. The membrane plug has a columnar body and at least one slot formed in the columnar body to vent pressure from the interior to the exterior of the capsule when the columnar body extends a predetermined distance relative to the second end of the capsule, thereby preventing expulsion of the membrane plug from the second end.