Abstract
The adsorption of lysozyme, bovine serum albumin (BSA) and fibrinogen onto the surfaces of a number of poly (methacrylate) based, phosphorylcholine (PC)-containing polymer films has been characterised by neutron reflection and spectroscopic ellipsometry. The work represents the first systematic study of these biocompatible materials, attempting to establish the relationship between the structure of the films and their effectiveness in reducing protein adsorption. The polymer surface was formed by dip-coating a thin film of polymer onto the polished silicon oxide. As the extent of reduction in protein adsorption may depend upon how the film is coated, initial work was to examine the effect of the coating conditions. We show that the improvement of the smoothness of the outer film surface can lead to the formation of a close-packed PC layer, resulting in the reduction of protein adsorption. The subsequent experiment was focused on the two model PC-polymers with (PC100B) and without (PC100A) 5% silyl cross-linking groups. It was found that although the structures of the films were drastically different, the residual amount of proteins adsorbed was comparable, indicating that the outer surfaces of the two films were similar in composition. The preliminary measurements using partially deuterated PC100B containing 5% silyl groups show that there is a preferential segregation of the hydrophobic and hydrophilic groups across the film, with the hydrophilic groups enriched at the outer surface. This work offers the first experimental evidence of the preferential expression of PC groups on the outer surface. In order to demonstrate the effectiveness of the PC-polymer surfaces in reducing protein adsorption, some parallel work has also been done on the model surfaces of bare SiO2, hydrophobed SiO2 and PMMA (polymethylmethacrylate). It was found that under similar solution conditions the PC-polymer surfaces can reduce protein adsorption by a factor of 3-5. It is particularly interesting that PC-polymer surfaces are most effective at deterring adsorption of large fibrous proteins, such as fibrinogen.