Table of Contents
Advances in Biomaterials
Volume 2014 (2014), Article ID 697491, 13 pages
http://dx.doi.org/10.1155/2014/697491
Research Article

In Vitro Corrosion Studies of Surface Modified NiTi Alloy for Biomedical Applications

1Surface Engineering Division, CSIR National Aerospace Laboratories, Post Bag No. 1779, Bangalore, Karnataka 560017, India
2Materials Science Division, CSIR National Aerospace Laboratories, Post Bag No. 1779, Bangalore, Karnataka 560017, India

Received 30 June 2014; Revised 1 October 2014; Accepted 21 October 2014; Published 20 November 2014

Academic Editor: William A. Brantley

Copyright © 2014 Manju Chembath et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Electropolishing was conducted on NiTi alloy of composition 49.1 Ti-50.9 Ni at.% under potentiostatic regime at ambient temperature using perchloric acid based electrolyte for 30 sec followed by passivation treatment in an inorganic electrolyte. The corrosion resistance and biocompatibility of the electropolished and passivated alloys were evaluated and compared with mechanically polished alloy. Various characterization techniques like scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy were employed to analyze the properties of surface modified and mechanically polished alloys. Water contact angle measurements made on the passivated alloy after electropolishing showed a contact angle of 35.6°, which was about 58% lower compared to mechanically polished sample, implying more hydrophilicity. The electrochemical impedance studies showed that, for the passivated alloy, threefold increase in the barrier layer resistance was obtained when compared to electropolished alloy due to the formation of compact titanium oxide. The oxide layer thickness of the passivated samples was almost 18 times higher than electropolished samples. After 14 days immersion in Hanks’ solution, the amount of nickel released was 315 ppb which was nearly half of that obtained for mechanically polished NiTi alloy, confirming better stability of the passive layer.