Fabrication, characterization and in-vitro evaluation of nanostructured zirconia/hydroxyapatite composite film on zirconium

• ZrO2/hydroxyapatite composite film was fabricated on Zr in a single step.
• Plasma electrolytic oxidation coupled electrophoretic deposition process was used.
• Hydroxyapatite particles were added to the electrolyte for film formation.
• ZrO2/hydroxyapatite film exhibits superior pitting corrosion resistance than Zr.
• Osteoblast cells show good adhesion and spreading on composite film.

The present study aims to fabricate ZrO2/hydroxyapatite [HA] composite film on Zr by plasma electrolytic oxidation coupled with electrophoretic deposition process in a single step. Further, ZrO2/HA film formation mechanism was studied as a function of treatment time in the range of 2 to 6 min in an aqueous electrolyte system consisting of dissolved tri sodium orthophosphate and suspended HA nanoparticles. The phase composition, surface morphology and elemental composition of the formed films were examined by X-ray diffraction [XRD], Raman spectroscopy and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Surface roughness, wettability, corrosion resistance, bioactivity and osteoblast cell adhesion characteristics of the ZrO2/HA film were also investigated. Uniform and dense ZrO2/HA films with thickness varying from 42 to 75 μm were formed at 2 to 6 min of treatment time. XRD results revealed that the films were comprised of nanocrystalline cubic zirconia and monoclinic zirconia. During the film growth process, HA particles were dragged into the discharge channels and subsequently entrapped into the oxide film by electrophoretic deposition. Additionally, calcium that originated from partial melting of HA enters the sites of Zr thereby stabilizing cubic ZrO2 phase. Raman spectrum confirmed the presence of HA phase along with ZrO2 phases. ZrO2/HA film exhibited better wettability and high surface energy compared to untreated Zr. Potentiodynamic polarization test revealed that the ZrO2/HA film formed at 6 min treatment time showed superior pitting corrosion resistance compared to untreated Zr in simulated body fluid [SBF] environment. Bone-like apatite layer was formed on entire surface of ZrO2/HA film after soaking in SBF for 8 days, indicating its significantly enhanced in-vitro bioactivity. Cell adhesion test results showed that the human osteosarcoma cells could attach, adhere and propagate well on the surface of ZrO2/HA film, suggesting the potential application of ZrO2/HA coated Zr as orthopedic implant material.