Injectable microencapsulated islet cells as a bioartificial pancreas.

Rat islets encapsulated in semipermeable membranes remained viable in culture for 4 months. Multiple allotransplants of islets encapsulated in alginate-polylysine-polyethyleneimine membranes restored normoglycemia in recipient diabetic rats for most of a 90-day experimental period. Each individual transplant restored normal fasting plasma glucose levels for 15-20 d. The failure of the encapsulated islets was caused by an inflammatory response induced by polyethyleneimine. In contrast a single transplant of islets encapsulated in a biocompatible alginate-polylysine-alginate membrane restored normoglycemia in recipient animals for up to 10 months. Capsules with intact membranes and containing viable islets were recovered from the abdominal cavity 5 months post-transplantation. SEM studies on capsule membranes revealed essentially smooth surfaces. Differences between wet and dry wall thicknesses indicated that the membrane is a hydrogel, 4.00 +/- 0.28 micron thick in an aqueous environment. The clinical potential of transplanting cells encapsulated in biocompatible semipermeable hydrogel membranes is demonstrated by this study.