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This dissertation, Surface Modification of NiTi for Long Term Orthopedic Applications by Yee-loi, Chan, 陳以來, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Surface Modification of NiTi for Long Term Orthopedic Applications Submitted by Chan Yee Loi for the degree of Master of Philosophy at The University of Hong Kong in August 2007 Near equi-atomic nickel-titanium (NiTi) shape memory alloys are unique materials displaying shape memory effect and superelasticity which make them attractive to the orthopedic field. With its high nickel content of 50at% there is concern on the safety use of this material for long period of time inside the human body as toxic nickel ions may released due to corrosion under physiological environment. These materials are also known to be bio-inert such that no chemical bond forms between bone tissue and NiTi upon surgical implantation and it may become prone to loosening. Plasma immersion ion implantation (PIII) was used in this study for creating a modified surface with increased corrosion resistant and bone bonding ability on NiTi whilst preserving its unique properties. Oxygen and sodium ions were sequentially implanted into the surface of NiTi discs. The modified NiTi were characterized in terms of surface chemistry, bioactivity, corrosion resistance, microstructure and in vitro biological performance using x-ray photoelectron spectroscopy (XPS), simulated body fluid immersion (SBF), anodic polarization scan, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and cell culture respectively. The same PIII treatment was applied to NiTi rods for determining the mechanical properties of bulk NiTi when the surface modification technique was upscaled. Presence of sodium and oxygen atoms in XPS data showed that PIII into NiTi was successful. SBF immersion proved that the bioactivity was enhanced upon implantation of sodium. Anodic polarization scan suggested that the corrosion resistance of plasma-implanted surfaces were significantly increased. Transformation temperatures of NiTi were slight shifted towards higher temperature after PIII as observed using DSC. No significant change in microstructure was revealed under TEM. Biological performance of surface modified NiTi was on par with NiTi if not better. At 37 C, plasma treated NiTi did not exhibit the same degree of superelasticity shown in NiTi. Plasma treated NiTi develops superelastcity similar to NiTi when the temperature was raised to 60 C. Sodium implantation on oxygen pretreated NiTi did not decrease the excellent corrosion resistance of oxygen PIII but instead enhanced its bioactivity by forming hydroxyl groups. The difference in mechanical properties between surface modified NiTi and NiTi was attributed to shifting of the transformation temperatures due to Joule heating during PIII which in turn affected the temperature-dependent superelasticity of NiTi. This heating could be managed via various factors including PIII instrumental parameters and cooling of the work piece such that, with proper design of these factors, control of the transformation temperatures and creation of the bioactive coating could be achieved in a single step. It was therefore concluded that PIII has the potential to modify the NiTi surface for increased bioactivity and corrosion resistance without deteriorating its biocompatibility. It was also suggested that Joule heating occurs during PIII such that transformation temperatures of NiTi may be changed and altering of mechanical per

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