Enhanced corrosion resistance and bio-performance of Al2O3 coated NiTi alloy improved by polydopamine-induced hydroxyapatite mineralization

Abstract Corrosion resistance and bio-performance of NiTi alloy is clinically important for osteointegrated implants with long-term performance. Though Al2O3 coating fabricated on NiTi alloy by the cathodic plasma electrolytic deposition (CPED) could effectively reduce the Ni ions release and improve the corrosion resistance to a large extent, the bioinert nature of Al2O3 coating will inevitably limit the potential for orthopaedic applications. In this study, hydroxyapatite (HA) was coated on the Al2O3 coating via polydopamine (PDA) induced biomimetic mineralization to improve the corrosion resistance, biocompatibility and in vitro bioactivity of the Al2O3-coated NiTi alloy. The surface morphology, phase composition, corrosion resistance, biocompatibility, and in vitro bioactivity of the samples with HA modified Al2O3 (HA/Al2O3) coating were systematically investigated. The results indicated that the Al2O3 coating surface was fully covered with HA minerals. The corrosion resistance of the HA/Al2O3-coated sample was enhanced by more than one order of magnitude than that of the Al2O3-coated NiTi alloy. The concentration of Ni ion release displayed a significant drop from 1.9 μg/mL for the Al2O3-coated NiTi alloy to 0.6 μg/mL for the HA/Al2O3-coated sample. In addition, the HA/Al2O3-coated NiTi alloy could promote the cell proliferation and osteogenic differentiation of human bone marrow mesenchymal stem cells (hMSCs) compared with the mere Al2O3-coated sample. Therefore, introducing the HA modified Al2O3 coating is a promising strategy for improving the corrosion resistance and bio-performance of NiTi alloy osteointegrated implants.