Collagen for sausage casing Devro patents： US7906623B2:Defatting collagen US7754258B2: Porcine collagen film US6235328: Process for producing a linked, coextruded ebible product US5944594：Apparatus and method for forming sausage links US4388331-Devro-1983-Collagen-sausage-casing US3535125A-Devro-1970-Edible-collagen-casing-manufacuring-process Now Viscofan: US2246236A-Naturin-1939-artificial-casing