Cell membrane mimetic films immobilized by synergistic grafting and crosslinking

Blood compatibility is a critical requirement for materials to be used in medical applications. We describe here a simple and robust method to enhance the biocompatibility of chitosan (CS) surfaces, using random copolymers (PMT) of 2-methacryloyloxyethyl phosphorylcholine (MPC) and trimethoxysilylpropyl methacrylate (TSMA, 6, 14, and 25 mol%) synthesized by free radical copolymerization. The copolymers dissolved in methanol were dip-coated on CS films. The PMT coatings were anchored on CS surfaces during the coating process by covalent bonding of the trimethoxysilane groups with surface amine and/or hydroxyl groups of CS. The composite films were stabilized by crosslinking of the copolymers via amine-catalyzed reactions of the trimethoxysilane groups and further heating (110 degrees C). Analysis of the PMT-modified CS surfaces by X-ray photoelectron spectroscopy and contact angle measurements indicated that the zwitterionic PC groups were located on or near the film outer surface, which mimics the structure of the cell outer membrane. Film stability studies indicated that PMT copolymers containing 14 mol% TSMA units were linked permanently to CS, whereas PMTs of lower TSMA content were released from the films upon prolonged soaking in water. The CS-PMT (14% TSMA) composite films possessed excellent hemocompatibility, as confirmed by a 60% decrease in protein (bovine serum albumin or fibrinogen) adsorption and a 96% suppression of platelet adhesion, compared to CS films. This simple and stable coating strategy should be useful in a variety of biomedical applications including drug delivery, tissue engineering, stent coatings, and implantable medical devices.