Effects of surface treatment on the surface chemistry of NiTi alloy for biomedical applications

Alloys of NiTi have gained popularity in biomedical applications; however, Ni is known to cause toxic and allergic reactions in the body, and concerns have been expressed regarding the material's biocompatibility. In this study, coupons of equiatomic NiTi were prepared by four methods, namely, mechanically polishing to a mirror finish, electropolishing, chemical etching and argon plasma etching, to produce various levels of roughness, and then examined by atomic force microscopy (AFM), XPS and AES. The resulting surface chemistry depended upon the method of preparation and was found not to be a function of surface roughness. The mechanically polished samples, although having the smoothest surface, showed the highest level of Ni in the near-surface region. The other preparation methods produced surfaces that were predominantly TiO2, with the electropolished surfaces showing the next smoothest surface and the least Ni in the near-surface region. The correlation between method of preparation, surface roughness and surface chemistry may be important in the preparation of NiTi for biomedical applications. (C) 1998 John Wiley & Sons, Ltd.