In vitro tribological behavior and corrosion resistance of SiO2/TiO2/ZrO2 coatings formed on the tantalum substrate using plasma electrolytic oxidation for orthopedic implant applications

Abstract

Tantalum (Ta) is widely used in orthopedic and dental implants due to its remarkable stability, biocompatibility, and mechanical properties. However, in physiological environments, even stable and noble metals can form harmful complexes. This study aimed to enhance the surface mechanical, topographical features, and biocompatibility of Ta by applying a coating of ZrO2, SiO2, and TiO2 nanoparticles using the plasma electrolytic oxidation (PEO) technique. A composite layer was formed on the Ta substrate through PEO at a constant voltage of 500 V with duty cycles of 20% and 40% for 10 min. Evaluation of the coated samples revealed significant improvements in various properties. The nanohardness of the Ta surface at a 40% duty cycle was found to be 6.7 times higher than that of the uncoated Ta sample. The stiffness of the coated Ta at a 40% duty cycle was 2.4 times higher than the uncoated Ta. However, the surface roughness of the 40% duty cycle-coated Ta was higher compared to other samples. The coated Ta at a 40% duty cycle exhibited a higher surface roughness and wettability, which can potentially enhance cell adhesion and proliferation. The surface morphology properties were analyzed using FESEM, which revealed the presence of a composite layer composed of ZrO2, SiO2, and TiO2 nanoparticles on the Ta substrate. Additionally, the contact angle test demonstrated that the coated Ta samples had decreased contact angles from 86° to 9°, indicating increased hydrophilicity compared to the uncoated Ta. Corrosion resistance was assessed through potentiodynamic polarization test and electrochemical impedance spectroscopy. The corrosion resistance of the coated Ta at 20% and 40% duty cycles increased from 0.78 × 103 Ω cm2 to 8.85 × 103 and 9.4 × 103 Ω cm2, respectively, indicating the formation of a nobler layer on the Ta surface. Biocompatibility studies using MG-63 cells showed enhanced cell adhesion and viability on the surface of the 40% duty cycle-coated Ta, attributed to its higher surface roughness and hydrophilicity. The cell viability for the coated samples (Ta-20 and Ta-40) after 3 days of culture was 95% and 98%, respectively, compared to 89% for the uncoated Ta sample. These findings demonstrate that the SiO2/TiO2/ZrO2 ceramic coatings significantly improve the mechanical properties, corrosion resistance, surface morphology, and hydrophilicity of Ta implants. Such enhancements have the potential to extend the lifetime of Ta implants in dental and orthopedic applications.