Ray W.Y. Poon

Suppression of Nickel Out-Diffusion from Porous Nickel-Titanium Shape Memory Alloy by Plasma Immersion Ion Implantation

Summary form only given. Porous nickel titanium is a promising material for medical application not only because of its super elasticity and shape memory effect but also the porous structure which may enhance bone growth due to the increased surface area. It is thus especially suitable for bone tissue in-growth and fixation of biomedical implants. However, like its dense counterpart, Ni leaching from the materials causes health concern. Thus, in order to suppress Ni diffusion from the materials to body fluids and tissues in humans, a diffusion barrier or similar structure must be introduced. In this work, we produced this diffusion barrier layer by oxygen or nitrogen plasma immersion ion implantation (PIII). In vitro tests were conducted by immersing the plasma-treated NiTi into simulated body fluid (SBF) at 37plusmn0.5degC for 5 weeks and the resulting SBF was analyzed for Ni and Ti using inductively-coupled plasma mass spectrometry (ICMPS). Our results show that Ni leaching is significantly mitigated by both nitrogen and oxygen PIII.

Effects of Temperature on the Effectiveness of the Surface Barrier Layers on Orthopedic Nickel-Titanium Shape Memory Alloys Fabricated by Nitrogen Plasma Implantation

Summary form only given. Nickel-titanium shape memory alloys (NiTi SMA) are potential orthopedic materials due to their super-elastic properties and shape memory effects. However, there are health and safety concerns with regard to the leakage of harmful Ni ions from the surface during prolonged use inside human beings. To mitigate this effect, we modified the alloy surface by plasma implantation of gas species such as nitrogen and oxygen. Our objection is to create barrier surface layers with graded interface to reduce Ni leaching from the NiTi substrate. The modified surfaces possess much improved electrochemical corrosion resistance, diminished Ni out-diffusion, and good biocompatibility according to our previous works. Since high temperature can degrade the elasticity of the NiTi SMA, suitable implantation parameters must be used to retain the mechanical properties of the bulk NiTi. In this work, we investigate the effects of the temperature on the effectiveness of the treatment process as well as the shape recovery. Our results show dependence of the shape recovery and surface barrier effectiveness on the treatment temperature