A membrane-mimetic barrier for cell encapsulation

A stabilized, membrane-mimetic film was produced on a polyelectrolyte multiplayer (PEM) by in-situ photopolymerization of an acrylate functonalized phospholipid assembly at a solid-liquid interface. The phospholipid monomer was synthesized, prepared as unilamellar vesicles, and fused onto close-packed octadecyl chains as part of an amphiphilic terpolymer anchored onto the PEM by electrostatic interactions. The lipid film displayed an advancing contact angle of similar to 60degrees, elemental composition, as determined by X-ray photoelectron spectroscopy, was in agreement with that anticipated for a lipid membrane. Data obtained from both high-resolution scanning electron microscopy and ellipsometry were consistent with the formation of a supported lipid monolayer. In addition, polarized external reflection infrared spectroscopy revealed significant acyl chain ordering induced on lipid fusion and polymerization. Doping the lipid assembly with a fluorescein terminated polymerizable lipid provided visible confirmation of film formation and its stability under a variety of conditions, including shear rates of 2000 sec(-1). Transport studies demonstrated that the addition of a lipid film significantly reduced barrier permeability for compounds in excess of 70 kD. The ability to coat microbeads (d similar to 300 mum) with a robust membrane-mimetic film, while preserving encapsulated cell viability is illustrated, thereby establishing a new strategy for modulating the physiochemical and biological properties of immunoisolation barriers for cell transplantation.