Chemical, physical, and mechanical characterization of chitosan coatings on a chemically pre-treated Ti6Al4V alloy

The coating of titanium with chitosan is a promising way to reduce the infection risk and to modulate the inflammatory response of bone implants, but no effective coating procedure exists at the moment. Two titanium surfaces are tested in this research: a mechanically polished (as reference) and a chemically pre-treated one. Three coating strategies are followed: the direct linking at different pH (acidic and neutral), covalent bonding through a chemical activation of the titanium substrate (tresyl chloride) or through a linker molecule (polydopamine). The obtained coatings have been characterized by means of SEM, AFM, FT-IR spectroscopy, zeta potential titration curves, tape adhesion test, and soaking at physiological pH for 2 weeks. The best results, in terms of the degree of the surface coverage and stability of the interface, are obtained on the chemically pre-treated surface. Comparing the different coating procedures, in descending order of efficacy, we find the direct linking at acidic pH, covalent bonding through chemical surface activation, use of a linker molecule, and direct linking at neutral pH. The combination of a proper coating procedure and pre-treatment of the surface is effective in enhancing the electrostatic bonding of the coating to titanium.