Highly Efficient Electrophoretic Deposition of Durable, Corrosion-Resistant Chitosan-PEG Composites on Metallic Implants

In this work, the electrophoretic deposition (EPD) of uniform and mechanically stable chitosan/poly(ethylene glycol) (PEG) films from a biphase H2O/CO2 medium under high pressure was proposed. This solvent has a pronounced sterilizing ability and spontaneously self-neutralizes during decompression, becoming a fully biocompatible medium. In such a medium, chitosan aggregates much less than in traditional acid solutions, which allows greater electrophoretic mobility of the macromolecules during EPD of the coating and contributes to an increase in the efficiency of the coating application. The addition of PEG improves the insufficient mechanical strength of the chitosan films, increasing their hardness and adhesion to the substrate. The average peel strengths were 0.15 ± 0.09 N mm–1 for the chitosan coating and 0.7 ± 0.2 N mm–1 for the chitosan/PEG composite. The interaction of chitosan and PEG, which form intermolecular complexes due to hydrogen bonding, was studied by Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction, and X-ray photoelectron spectroscopy methods. The contact angles of water droplets on the obtained coatings are in the optimal range for bone cell proliferation: 35–85°. High biocompatibility of the coatings was confirmed by evaluating the cytotoxicity using the methyl-thiazol tetrazolium assay with C2C12 osteo-like cells. The coatings show good corrosion resistance due to their high adhesion to metal. Composite coating demonstrated a shift in the corrosion potential toward positive values by 0.1 V, and a drop in corrosion current density by an order of magnitude as compared to the bare titanium substrate. The morphology of the coatings was evaluated by atomic force microscopy, scanning electron microscopy, and profilometry methods, and it was shown that the addition of PEG leads to a significant decrease in the coating thickness (2 μm), while increasing the uniformity. The roughness of the coatings is in the submicron range.