Polyurethane-Polydimethylsiloxane (PU-PDMS) tubular membranes for pancreatic islet transplantation: Permselectivity and diffusion studies

Transplantation of immuno-protected xenogenic islets of Langerhans by a permselective synthetic membrane represents an intriguing possibility to treat the diabetic disease. In this study, polymeric tubular membrane with a porous wall structure and an internal permselective layer (skin) were fabricated by a combination of spraying and phase-inversion of a thermodynamically unstable solution of a biocompatible PU (90%)-PDMS (10%) blend (Cardiothane(TM) 51) over a sliding and rotating mandrel. Segments of tubular membranes were capped at both extremities according to the "macroencapsulation" technique. Reference compounds of different molecular masses were used to evaluate capsules permselectivity characteristics, while glucose, insulin and porcine islets of Langerhans were used to study the diffusion properties. The results of these studies showed the capsules to be impermeable to compounds with a molecular mass higher than approximately 40 000 Da, but permeable to glucose and insulin. Pancreatic islets entrapped within the capsules released, over a 2 h period, insulin proportionally to the glucose concentration in the medium without a significant difference in comparison with the amount of insulin released by non-encapsulated islets. Finally, potential drawbacks deriving from an inaccurate capsules sealing and from the severity of the host tissue reaction versus the structural material are discussed.