Design of a polyurethane membrane for the encapsulation of islets of Langerhans

A semipermeable membrane for the encapsulation of the islets of Langerhans, consisting of a microporous polymer network, has been developed. The polyurethane network was formed by cross-linking a mixture of linoleic acid and a linear poly(etherurethane) with dicumyl peroxide. Cross-linking the polyurethane impedes the formation of hard domains. Miocroporosity was introduced by adding salt crystals of different sizes before cross-linking and leaching it out afterwards. To optimize the permeability and immunoprotectivity, membranes were prepared with three different porosities. Membranes of this material were filled with islets of Langerhans and implanted in the peritoneal cavity of rats. Short-term in vivo experiments in rats show that membranes with pores in the range 0.3-0.7 micron and a wall thickness of about 8 microns were permeable for insulin and glucose and protected the islets of Langerhans against the cells of the immunological system.