Plasma electrolytic oxidation as an effective tool for production of copper incorporated bacteriostatic coatings on Ti-15Mo alloy

This report describes the plasma electrolytic oxidation (PEO) treatment of Ti-15Mo alloy surfaces in baths containing 0.1 M Ca(H2PO2)2 with different insoluble copper-based additives: CuO or Cu3(PO4)2. The aim of this work was to fabricate oxide coatings with bacteriostatic and cytocompatible properties. The surface morphology, roughness, and wettability (based on dynamic water contact angle measurements) of the oxide coatings were evaluated. Additionally, the presence of copper compounds and bioactive calcium and phosphorus in the investigated oxide coatings was confirmed using various spectroscopic and crystallographic techniques. The highest copper concentration (3.5 at.%) was detected in the oxide layer obtained using a PEO suspension bath comprising Cu3(PO4)2 and Ca3(PO4)2. The oxide coating generated from a PEO bath containing CuO had the lowest copper concentration (0.1 at.%). The bacteriostatic properties of the obtained Cu-doped oxide layers were established based on bacterial adhesion tests using Gram-positive Staphylococcus aureus (ATCC 25923) and Gram-negative Escherichia coli (ATCC 25922). On the Cu-incorporated surfaces, the number of surface-adhered bacterial colonies was ~10–100 times lower than on the reference Ti-15Mo surface, and ~105 times lower than on tryptic soy broth medium. The materials’ cytocompatibilities were confirmed through tests with MG-63 osteoblast-like cells.