Construction of TiO₂/silane nanofilm on AZ31 magnesium alloy for controlled degradability and enhanced biocompatibility

A TiO₂ nanofilm was prepared on the surface of AZ31 magnesium alloy with controllable thickness through atomic layer deposition (ALD) technique, which can adjust the corrosion behaviors of AZ31 Mg alloy. Compared with the untreated Mg alloys, corrosion current densities (i_corr) can decline by 58% in the 200-cycles TiO₂-covered Mg alloy and further decline by up to 74% with the thickness of nanofilm up to 63 nm (400 cycles). The subsequent modification with a cross-linked conversion layer of 3-amino-propyltriethoxysilane (APTES) by a dipping method can produce a compact silane coating on TiO₂ nanofilm, which can seal pinholes of TiO₂ nanofilm and serve as a barrier to further adjust the corrosion behavior of the substrate. The i_corr can decline about two orders of magnitude in the TiO₂/silane composite coating. Making the adjustable corrosion rate come true, which can be attributed to the precise control on the thickness of metal oxide nanofilm and additional protection from the compact silane coating. In vitro study discloses that the TiO₂/silane hybrid coating shows higher expression of alkaline phosphatase (ALP) and can promote cellular adhesion and proliferation with better cytocompatibility than untreated Mg alloy.