Hydrophilic thin films formation on AZ31 alloys by hydrothermal treatment in silicate containing solution and the evaluation of corrosion protection in phosphate buffered saline

Magnesium alloys have been widely studied as biodegradable implants for orthopedic applications due to their more suitable mechanical and biological properties. However, Mg and its alloys themselves don't have high hydrophilicity considered to be effective in improving the osteoconductivity of implanted materials. The drastic degradation rate of Mg alloys would also cause potential harm to the human body. With the aim to promote the hydrophilicity and corrosion resistance of Mg alloys, thin film consisting of magnesium hydroxide with silicate was synthesized by hydrothermal treatment in the alkaline solution of sodium hydroxide and sodium silicate at 423 K. The physical properties of thin films were estimated by SEM, XRD, XPS, tape peeling test and water droplet contact angle (WCA), and corrosion properties were evaluated by polarization curves and impedance measurements (EIS) in PBS solution. Mg(OH)₂ was found to be the main composite of the film with little of MgO coexisted. Si was detected on the surface of the film layer, based on XPS results. The addition of silicate during hydrothermal treatment would greatly improve the hydrophilicity and its stability in the air environment. The Mg(OH)₂ film containing Si also indicated higher corrosion resistance. (paper)