Preparation and in vitro antibacterial properties of anodic coatings co-doped with Cu, Zn, and P on a Ti–6Al–4V alloy

In this study, copper (Cu) and zinc (Zn) as well as phosphorus (P) were co-doped into a Ti–6Al–4V titanium alloy via micro-arc oxidation (MAO). The entrance mechanisms of Cu and Zn into MAO coatings were investigated by an orthogonal experiment. The results show that Cu and Zn in Cu–Zn–P coatings separately exist mainly in the forms of Cu2O and Zn3(PO4)2. The Cu content in MAO coating increases with increasing EDTA-CuNa2 and KOH concentrations and decreasing phytic acid concentration but is nearly independent of EDTA-ZnNa2 concentration. The Zn content increases with increasing EDTA-ZnNa2 concentration and decreasing EDTA-CuNa2 concentration, indicating the competing effect between Cu and Zn for incorporation into Cu–Zn–P coatings. Compared with Zn ions, Cu ions do not readily enter anodic coatings due to their simultaneous involvement in coating formation on the anode and precipitation of metallic copper on the cathode. Cu–Zn–P coatings with appropriate amounts of Cu and Zn achieve excellent antibacterial ability against Escherichia coli (E.coli), Staphylococcus aureus (S.aureus), and Methicillin-resistant Staphylococcus aureus (MRSA). These antibacterial properties, in addition to excellent cytocompatibility, make Cu–Zn–P coatings as promising materials for orthopedic applications.