Formation of self-layered hydrothermal coating on magnesium aided by titanium ion implantation: Synergistic control of corrosion resistance and cytocompatibility

The self-layered phenomenon has been observed from the hydrothermal processing of magnesium and Mg alloys, but it is still difficult to controllably fabricate a self-layered hydrothermal (SLH) coating due to the unclear formation mechanism and complex influencing factors. In this work, titanium ion implantation is adopted as a trigger process to modify the surface of pure magnesium and induce the formation of self-layered hydrothermal film. Compared to the conventional hydrothermal process that yields a relatively smooth and single-layer coating on pure magnesium, this new method produces a magnesium hydroxide-based SLH coating composed of an inner compact layer and outer nanosheet-based layer. Characterization results show that a Ti-implantation layer with titanium nanocrystals embedded in Mg matrix was formed after Ti-ion implantation. The galvanic effect between Ti nanocrystal and magnesium matrix accelerates corrosion and consequently, Mg(OH)₂ nanosheets are formed from precipitation in the rapidly supersaturated solution of magnesium ions and hydroxide ions. For the as-prepared SLH coating, the inner compact layer provides good corrosion protection, while the outer layer improves functional properties such as cell adhesion and cytocompatibility. With synergistic improvement of corrosion resistance and cytocompatibility, the ion implantation-induced SLH coating is promising for further application in biomedical magnesium materials.