A spatially defined Sr/Zn gradient coating with dual osteogenic and anti-corrosion functions on Ti6Al4V via softened spark MAO

Abstract

In order to overcome the problems of highly interconnected pores and insufficient long-term corrosion resistance in micro-arc oxidation (MAO) coatings this study integrated softened spark MAO (S-MAO) with a Sr²⁺/Zn²⁺ complexation regulation strategy to fabricate composite MAO coatings on Ti6Al4V implant surfaces. The S-MAO treatment transformed coating architecture from a bilayer into a three-layer gradient structure (barrier layer/softened-spark layer/porous layer). This significantly diminished the interconnectedness of interior pores. Electrochemical tests showed that the way S-MAO coatings corrode changed from diffusion control to the interfacial charge transfer process being the most important. This indicates that the coatings' electrochemically protective qualities are more stable. The Z₁S₃MAO coating, with a Sr/Zn ratio of 3 : 1, demonstrated elevated interfacial charge transfer resistance (443.6 Ω cm²) and enhanced impedance responsiveness. The examination of the elemental distribution showed that Sr was spread out evenly throughout the coating thickness. However, Zn had a localized enrichment zone at the interface between the softened-spark layer and the porous outer layer. The spatial distribution is determined by the varying stability of ion complexation. The Z₁S₃MAO coating exhibited superior performance regarding wettability and cytocompatibility associated with osteogenesis.