Fabrication of bioactive titania coating on nitinol by plasma electrolytic oxidation

• Published in: Applied surface science 2013-06, Vol.274, p.181-187
• Main Authors: Siu, H.T., Man, H.C.
• Format: Article
• Language: English
• Subjects: Apatite; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Corrosion; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Nickel Titanium (NiTi); Physics; Plasma Electrolytic Oxidation (PEO); Titanium Oxide
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2013.03.008

•Thick and porous TiO2 was fabricated on NiTi by plasma electrolytic oxidation.•By using an appropriate electrolyte and a low voltage, anatase was formed.•The corrosion resistance in Hanks’ solution is significantly improved.•The surface Ni content is greatly reduced.•The plasma-electrolytic oxidized NiTi possesses high apatite-forming ability. Surface modification was attempted on Nitinol (NiTi) by plasma electrolytic oxidation (PEO) in aqueous solutions of sodium sulphate and sodium hydroxide (Na2SO4-NaOH) using an AC power supply. A thick and porous oxide layer with micron-sized pores was formed on the Nitinol substrate, with the thickness of the oxide layer ranging from a few μm to over 10μm, depending on the processing time. X-ray diffraction (XRD) analysis confirmed that the oxide formed was anatase. Potentiodynamic polarization tests in Hanks’ solution showed that the corrosion resistance of PEO-coated Nitinol was much higher than that of the substrate. More importantly, the apatite-forming ability of the PEO-treated NiTi was found to be enhanced. This could be attributed to the anatase crystalline structure of the titanium oxide and the porous structure that facilitates the anchorage of the hydroxyapatite particles.