Zn and Ag Co-doped Anti-microbial TiO2 Coatings on Ti by Micro-arc Oxidation

Micro-porous TiO2 coatings co-doped with Zn2+ and Ag nanoparticles were fabricated on Ti by micro-arc oxidation (MAO) for 0.5, 1.5, 2 and 4 min, respectively. The evolutions of morphology and phase component of the coating as a function of processing time were investigated. The microstructure of the 2 min treated coating was further observed by transmission electron microscopy to explore the coating formation mechanism. The amounts of Ag and Zn released from the 2 min treated coating were measured and the antibacterial properties of the coatings against Staphylococcus aureus (S. aureus) were also investigated. The obtained results showed that with prolonged MAO time, the contents of Ag and Zn on the coating surfaces increased. All the coatings were micro-porous with pore diameters of 1-4 µm; however, some pores were blocked by deposits on the 4 min treated coating. The 2 min treated coating was composed of amorphous TiO2, anatase, rutile, ZnO, Zn2TiO4 and homogenously distributed Ag nanoparticles. After immersion, Zn2+, Ag+, Ti2+ and Ca2+ were released from the coating and with the immersion time prolonged, the accumulated concentrations of these ions increased. After immersion for 36 weeks, the accumulated Zn2+ and Ag+ concentrations were 6.88 and 0.684 ppm, respectively, which are higher than the minimal inhibitory concentration but much lower than the cytotoxic concentration. Compared with polished Ti control, the coatings co-doped with Zn2+ and Ag nanoparticles significantly inhibited the adhesions of S. aureus and reduced the amounts of planktonic bacteria in culture medium, indicating that the Zn and Ag co-doped TiO2 could be a bio-adaptable coating for long-lasting anti-microbial performance.