Neovascularization of synthetic membranes directed by membrane microarchitecture

Transplantation of tissues enclosed within a membrane device designed to protect the cells from immune rejection (immunoisolation) provides an opportunity to treat a variety of disease conditions. Successful implementation of immunoisolation has been hampered by the foreign‐body reaction to biomaterials. We screened a variety of commercially available membranes for foreign‐body reactions following implantation under the skin of rats. Histologic analysis revealed that neovascularization at the membrane–tissue interface occurred in several membranes that had pore sizes large enough to allow complete penetration by host cells (0.8‐8‐μm pore size). When the vascularization of the membrane–tissue interface of 5‐μm‐pore‐size polytetrafluoroethylene (PTFE) membranes was compared to 0.02‐μm‐pore‐size PTFE membranes, it was found that the larger pore membranes had 80–100‐fold more vascular structures. The increased vascularization was observed even though the larger pore membrane was laminated to a smaller pore inner membrane to prevent cell entry into the prototype immunoisolation device. This significantly higher level of vascularization was maintained for 1 year in the subcutaneous site in rats. © 1995 John Wiley & Sons, Inc.