MICROENCAPSULATION OF ISLETS IN PEG-AMINE MODIFIED ALGINATE-POLY(L-LYSINE)-ALGINATE MICROCAPSULES FOR CONSTRUCTING BIOARTIFICIAL PANCREAS

Two positively charged derivatives of poly(ethylene glycol) (PEG) were coated onto alginate-poly(L-lysine)-alginate (A-P-A) microcapsules by allowing them to interact them with the negatively charged alginate o n the capsule surface. The polymers are methoxypolyoxyethylene amine ( PEGA1) and polyoxyethylene bis(amine) (PEGA2), which contain charged a mine groups at one or both ends, respectively, with PEG as the backbon e. The coating of the microcapsules with PEG-amine resulted in a much smoother capsule surface than A-P-A microcapsule surfaces as examined under a scanning electron microscope. The diffusivity of bovine serum albumin into the microcapsules remained the same after PEGA1 coating. But the diffusivity decreased to less than one-fifth that in A-P-A mic rocapsules coated with PEGA2. The biocompatibility of the microcapsule s also improved as investigated by an in vivo study. Microcapsules wer e implanted in the peritoneal cavity of BALB/c mice and retrieved 120 d after implantation. The fibrotic action against A-P-A microcapsules was severe and the capsules retrieved by peritoneal lavage aggregated into clusters. In contrast, the surface-modified capsules were free-fl owing and free of cell overgrowth. Secretion of insulin from rat islet s within A-P-A-PEGA microcapsules responded well to changes in glucose concentration in a static glucose test. Intraperitoneal transplantati on of the microencapsulated islets into streptozotocin-induced diabeti c mice could maintain normal blood glucose levels in test animals for up to 200 d without immunosuppression.