The Reduced Adsorption of Proteins at the Phosphoryl Choline Incorporated Polymer−Water Interface

Abstract

The adsorption of lysozyme and bovine serum albumin (BSA) onto the surface of a hydrogel polymer has been characterized by neutron reflection and spectroscopic ellipsometry. The polymeric hydrogel was synthesized by copolymerizing methacrylate monomers bearing dodecyl chains and phosphorylcholine (PC) groups. The polymer surface was formed by dip-coating a thin layer of the polymer onto the polished surface of silicon oxide. While ellipsometric measurements at the solid−water interface showed that the polymer film could be represented by a uniform layer of 55 ± 5 Å, the subsequent measurements from neutron reflection suggested that the structural profile of the polymeric film was better described by a three layer model: the inner layer of 30 ± 3 Å mixed with less than 20% water, the middle layer of 20 ± 5 Å mixed with approximately 40% water, and the outermost layer of 25 ± 3 Å mixed with approximately 85% water. The neutron results thus suggest the uneven swelling of the polymer film along the direction normal to the interface. The adsorption of lysozyme and BSA onto the polymer surface was measured over a wide protein concentration range. It was found that the amount of proteins adsorbed on the coated polymer surface was substantially lower than that at the bare silica−water interface under the same solution condition. Thus, the amount of BSA adsorbed onto the polymer-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 interface. In addition, the amount of lysozyme adsorbed onto the coated surface at pH 7 and at 1 g dm-3 was also found to be about 0.5 mg m-2, as compared with 3.5 mg m-2 at the silica−water interface. The reduction in protein adsorption was attributed to the presence of a PC layer preferably formed on the outer surface of the coated polymer film.