Degradation behavior, biocompatibility and antibacterial activity of plasma electrolytic oxidation treated zinc substrates

A ZnO/Zn(OH)2 hybrid coating was fabricated in situ via plasma electrolytic oxidation (PEO) in Na2CO3 electrolyte on pure Zn surface for elucidating the influence of PEO treatment on the degradation behavior of Zn and Zn-based materials. Degradation effects, including surface morphology evolution, corrosion product generation and degradation rate, were systematically investigated through simulated body fluid (SBF) immersion and Hank's solution immersion tests. The results confirm that PEO treatment accelerates the degradation of Zn. With the rise in applied voltage, the initial degradation rate decreases from 0.60 to 0.20 mm/year, whereas the long-term degradation rate can reach 0.50–0.70 mm/year. Especially, the degradation rate acquired at 400 V could meet the general design criteria for degradation rate of biodegradable metallic devices. The corrosion products mainly consist of Zn(OH)2, ZnO, Zn3(PO4)2 and CaP matters. They aggregate to form a bi-layer on the as-formed PEO coating surface. Furthermore, the good in vitro biocompatibility and antibacterial properties of the PEO-treated Zn indicate that PEO is a promising method to treat Zn and Zn-based implants for orthopedic application. When the applied voltage is 400 V, the increased hydrophilicity (WCA <25°), good biocompatibility (cell viability >100 %) and the best enhanced antibacterial performance (53.3 % for S. aureus, 88.3 % for E. coli) compared to that of pure Zn are observed.