Biomechanical compatibility and electrochemical stability of HA/Ta2O5 nanocomposite coating produced by electrophoretic deposition on superelastic NiTi alloy

In this paper, natural hydroxyapatite (nHA) and nHA/20 wt% Ta2O5 coatings were electrophoretically deposited on NiTi. Phase analysis and microstructural characterizations of coatings were accomplished using X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). Micro-indentation examination results revealed that nHA/Ta2O5 coating has the most compliant elastic modulus (32.85 GPa) to that of the adjacent bone tissue. Adhesion strength of coatings that was determined with tensile as well as nano-scratch tests affirmed the better adhesion properties of nHA/Ta2O5 compared with nHA coating on NiTi. Fracture toughness calculations from nano-scratch data exhibited the highest value for nHA/Ta2O5 coating (1 MPa m(1/2)). Degradation behaviors of nHA and nHA/Ta2O5 coated NiTi in Phosphate Buffered Saline (PBS) solution were characterized by electrochemical impedance spectroscopy (EIS) technique during 30 days of immersion. Time-dependent evolution of open circuit potentials and impedance characteristics' results clarified the positive role of Ta2O5. Reasons for this improvement were explained by the lower amounts of open porosities and easier blocking of pores in the presence of Ta2O5. (C) 2019 Elsevier B.V. All rights reserved.