Protein adsorption on soft contact lenses. III. Mucin

Adsorption of bovine submaxillary mucin (BSM) on three different soft contact surfaces, lathe cut (LC) and spin cast (SC) crosslinked poly-2-hydroxyethylmethacrylate and spin cast poly(2-hydroxyethylmethacrylate/methacrylic acid) (PHEMA/MAA), was studied. The in vitro process was followed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). A three-layer structure is envisaged for the adsorbed BSM: a very thin surface layer of strongly bound and conformationally altered mucin constitutes the surface layer. A random to beta-sheet structural transition activated by the hydrogel surface is proposed for this layer. Glycoprotein hydrogen-bonding with the polymer hydroxyls and interaction of charged and hydrophobic groups with hydrogel surfaces are important in stabilizing this layer. Most of the adsorbed BSM (99%) is found in the middle and top layers which are formed by a different degree of associated BSM (their conformation is minimally changed or not changed at all, respectively) and are weakly adsorbed to the lens surfaces. Surface morphology and chemical composition of the lenses are important adsorption parameters only for the reversibly adsorbed BSM.