Biomedical coatings by the covalent immobilization of polysaccharides onto gas-plasma-activated polymer surfaces

Abstract

As the surface properties of polymeric biomaterials play an important role in the performance of biomedical devices, highly hydrophilic, ultrathin coatings were applied onto hydrophobic, perfluorinated and organosilicon polymers by the covalent immobilization of polysaccharides using a reductive amination reaction. Gas plasma (r.f. glow discharge) methods were employed to equip the surfaces of these normally unreactive polymeric substrates with chemical groups capable of reacting with polysaccharides in aqueous solution. In one variant, ammonia plasmas were used to introduce into the polymer surfaces a submonolayer of amine groups. Alternatively, an n-heptylamine process vapour was used to deposit a thin plasma polymer film that possessed surface amine groups. The polysaccharides were activated for covalent immobilization by periodate oxidation, which produced hemiacetal structures, as revealed by NMR and XPS. The hemiacetal structures in the polysaccharide chains were reacted with the surface amine groups on the polymers. The resulting Schiff base linkages were stabilized by reduction to secondary amine linkages using sodium cyanoborohydride. Detailed surface analysis is important for verification that the intended chemistries have indeed been achieved in such multilayer coating schemes. X-ray photoelectron spectroscopy provided a thickness estimate of 1 ± 0.3 nm for the polysaccharide coatings in the dehydrated state. Copyright © 2000 John Wiley & Sons, Ltd.