Preparation of biocompatible polymeric thin films by layer-by-layer assemblies of chitosan and poly(Styrene sulfonate)

Abstract

Ultrathin polymer films were prepared by an alternate adsorption between anionic poly(styrene sulfonate) (PSS) and cationic chitosan (CHI) on the amine functionalized silicon substrate (Si-NH2) at pH 4. The assembly process was monitored by ellipsometric measurement. Thickness of film was strongly dependent on NaCl concentration in polymer solution. The film thickness increased upon increasing the NaCl concentration. Zeta-potential and water contact angle data indicated that the multilayer were stratified and the charge was reversed after each deposition. The results indicated that each individual layer was sufficiently thick so that surface properties depended upon the last deposited layer. X-ray photoelectron spectroscopy (XPS) and Attenuated total reflectance infrared spectroscopy (ATR-IR) were also used to confirm the layer formation. As determined by atomic force microscopy, it was found that the thicker the assembled film, the rougher the surface. The results of blood compatibility suggested that the roughness played a dominant role in controlling the protein adsorption and platelet adhesion. This observation also implied that the platelet response was dictated not only by the amount of adsorbed protein but also by the topography of the surface, especially when the surface became really rough.