Microstructure, nickel suppression and mechanical characteristics of electropolished and photoelectrocatalytically oxidized biomedical nickel titanium shape memory alloy

Research output: Journal Publications and ReviewsRGC 21 - Publication in refereed journalpeer-review

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Author(s)

  • C. L. Chu
  • C. Guo
  • X. B. Sheng
  • Y. S. Dong
  • P. H. Lin
  • K. W K Yeung

Detail(s)

Original languageEnglish
Pages (from-to)2238-2245
Journal / PublicationActa Biomaterialia
Volume5
Issue number6
Publication statusPublished - Jul 2009

Abstract

A new surface modification protocol encompassing an electropolishing pretreatment (EP) and subsequent photoelectrocatalytic oxidation (PEO) has been developed to improve the surface properties of biomedical nickel titanium (NiTi) shape memory alloy (SMA). Electropolishing is a good way to improve the resistance to localized breakdown of NiTi SMA whereas PEO offers the synergistic effects of advanced oxidation and electrochemical oxidation. Our results indicate that PEO leads to the formation of a sturdy titania film on the EP NiTi substrate. There is an Ni-free zone near the top surface and a graded interface between the titania layer and NiTi substrate, which bodes well for both biocompatibility and mechanical stability. In addition, Ni ion release from the NiTi substrate is suppressed, as confirmed by the 10-week immersion test. The modulus and hardness of the modified NiTi surface increase with larger indentation depths, finally reaching plateau values of about 69 and 3.1 GPa, respectively, which are slightly higher than those of the NiTi substrate but much lower than those of a dense amorphous titania film. In comparison, after undergoing only EP, the mechanical properties of NiTi exhibit an inverse change with depth. The deformation mechanism is proposed and discussed. Our results indicate that surface modification by dual EP and PEO can notably suppress Ni ion release and improve the biocompatibility of NiTi SMA while the surface mechanical properties are not compromised, making the treated materials suitable for hard tissue replacements. © 2009 Acta Materialia Inc.

Research Area(s)

  • Microstructure, Nanoindentation, NiTi shape memory alloy, Photoelectrocatalytic oxidation, Titania film

Citation Format(s)

Microstructure, nickel suppression and mechanical characteristics of electropolished and photoelectrocatalytically oxidized biomedical nickel titanium shape memory alloy. / Chu, C. L.; Guo, C.; Sheng, X. B. et al.
In: Acta Biomaterialia, Vol. 5, No. 6, 07.2009, p. 2238-2245.

Research output: Journal Publications and ReviewsRGC 21 - Publication in refereed journalpeer-review