The reduced adsorption of proteins at the phosphoryl choline incorporated polymer-water interface

The adsorption of lysozyme and bovine serum albumin (BSA) onto the surface of a hydrogel polymer has been characterized by neutron reflection and spec troscopic ellipsometry. The polymeric hydrogel was synthesized by copolymer izing methacrylate monomers bearing dodecyl chains and phosphorylcholine (P C) groups. The polymer surface was formed by dip-coating a thin layer of th e polymer onto the polished surface of silicon oxide. While ellipsometric m easurements at the solid-water interface showed that the polymer film could be represented by a uniform layer of 55 +/- 5 Angstrom, the subsequent mea surements from neutron reflection suggested that the structural profile of the polymeric film was better described by a three layer model: the inner l ayer of 30 +/- 3 Angstrom mixed with less than 20% water the middle layer o f 20 +/- 5 Angstrom mixed with approximately 40% water, and the outermost l ayer of 25 +/- 3 Angstrom mixed with approximately 85% water. The neutron r esults thus suggest the uneven swelling of the polymer film along the direc tion normal to the interface. The adsorption of lysozyme and BSA onto the p olymer surface was measured over a wide protein concentration range. It was found that the amount of proteins adsorbed on the coated polymer surface w as substantially lower than that at the bare silica-water interface under t he same solution condition. Thus, the amount of BSA adsorbed onto the polym er-coated surface at pH 5 and at 0.05 g dm(-3) was found to be less than 0. 5 mg m(-2),as compared with 2 mg m(-2) obtained at the bare silica-water in terface. In addition, the amount of lysozyme adsorbed onto the coated surfa ce at pH 7 and at Ig dm(-3) was also found to be about 0.5 mg m(-2), as com pared with 3.5 mg m(-2) at the silica-water interface. The reduction in pro tein adsorption was attributed to the presence-of a PC layer preferably for med on the outer surface of the coated polymer film.