Cytomimetic Biomaterials. 2. In-Situ Polymerization of Phospholipids on a Polymer Surface

A stabilized, phosphatidylcholine-containing polymeric surface was produced by in-situ polymerization on an amphiphilic polymer surface. The phospholipid monomer, 1-palmitoyl-2-[12-(acryloyloxy)dodecanoyl]-sn-gycero-3-phosphorylcholine, was prepared as unilamellar vesicles and fused onto a terpolymer consisting of the monomers 2-(methylthio)ethyl methacrylate, 2-hydroxyethyl acrylate, and 3-acryloyl-3-oxapropyl-3-(N,N-dioctadecylcarbamoyl)propionate. Free-radical polymerization was carried out in aqueous solution at 70 °C using the water-soluble initiator, 2,2‘-azobis(2-methylpropionamidine) dihydrochloride. The supported monolayer displayed advancing and receding water contact angles of 58° and 31°, respectively. Angle-dependent electron spectroscopy for chemical analysis (ESCA) results confirmed the presence of phosphorus and nitrogen and was consistent with theoretical predictions for a close-packed monolayer. Ellipsometry measurements indicated a film thickness of 134 Å. In the absence of network formation, polymeric films demonstrated acceptable stability under static conditions in water. For comparative analysis, the phospholipid was also fused and polymerized onto a self-assembled monolayer of octadecyl mercaptan (ODT) bound to gold. ESCA data were consistent with a close packed monolayer and ellipsometry revealed a film thickness of 66 Å. Nonetheless, contact angle measurements demonstrated that the polymerized lipid monolayer when supported on an ODT surface exhibited a higher level of instability over time than that supported by the amphiphilic terpolymer.