Biocompatibility and Mechanical Performance of Ni-Ti

Abstract

Biomimetic apatite deposition behaviors and mechanical performance for as-rolled and annealed Ni-Ti plates were investigated. Apatite nucleation and growth on Ni-Ti in SBF (simulated body fluid) was not appreciably influenced by heat treatment. But, the apatite deposition rate increased slightly by NaOH surface treatment. The nodular apatite on the deposited layer is favored on a macro-scale since the surface energy of polycrystalline apatite particles can be reduced by forming nodules. The weight gain after apatite deposition for Ni-Ti (0.004 g/cm2) after 10 days were found to be smaller that that of NaOH treated Ti-6Al-4V, but it was comparable to that of non- NaOH-treated Ti-6Al-4V (0.004 g/cm2). The stress-strain responses of annealed Ni-Ti displayed the pseudoelastic behavior associated with stress-induced martensite formation with the transition stress for the martensite formation equal to 320 MPa. On the other hand the cold worked Ni-Ti displayed no appreciable pseudoelastic region and the yield stress was ~500MPa. A good biomimetic apatite formation and excellent mechanical performance of Ni-Ti suggests that Ni-Ti can be an excellent candidate material for orthopedic implants.