Protein adsorption on functionalized and ESCA-characterized polymer films studied by ellipsometry

Abstract

The adsorption of bovine serum albumin (BSA), immunoglobulin G (IgG), fibrinogen, and poly- l-lysine (PLL) on polyvinylchloride (PVC), a copolymer of methacrylic acid/methacrylate (PMA) and surface-grafted polyethylene oxide (PEO) films, has been studied by means of ellipsometry. The films were spin-cast on silicon wafers covered with silicon oxide (SiO x ). Under physiological conditions, most proteins, but not the polyelectrolyte PLL, adsorbed to a larger extent to the hydrophobic PVC than to the hydrophilic PMA or PEO surfaces. For PLL extensive adsorption to PMA occurred as a result of strong electrostatic interaction. A correlation was found between the amount of protein adsorbed as measured by ellipsometry, and the relative surface content of nitrogen as recorded using ESCA. None of the proteins adsorbed to a constant plateau level. Instead, a monotonically increasing degree of adsorption was found in the concentration range studied, 0–1000 g/m 3. For the hydrophobic PVC, the isotherms were similar in shape to those theoretically obtained by I. Lundström ( Prog. Colloid Polym. Sci. 70, 76–82 (1985)) upon assuming a dynamic adsorption process which takes into account several modes of adsorption characterized by different affinities to the surface. Generally, a low degree of protein adsorption, Γ < 0.5 mg/m 2, was observed for surfaces covered with PEO chains (mol wt 1900) which were covalently linked, by means of terminal CHO groups, to surface amino groups.