The future of Nitinol (a NiTi alloy) as a biomaterial depends crucially on its surface characteristics. If the problem with possible Ni release from Nitinol implants could be solved through the design of a stable and inert surface, Nitinol would be superior to every other metallic biomaterial available at least through the first century of the new millenium. Efforts to modify the Nitinol surfaces using artificial coatings, laser and plasma treatments or ion implantation have not succeeded. The resulting surfaces are either enriched in Ni and are not passive, or degrade during shape recovery. A more promising direction to pursue, in the search for biocompatible surfaces, is chemical and electrochemical modification of native NiTi, to produce surface layers that do not crack and spall off during shape recovery of a device/implant. Therefore, we propose: 1) To design biocompatible, highly corrosion-resistant NiTi surfaces employing simple, cost-effective chemical and electrochemical procedures. 2) To use X-ray Photoelectron Spectroscopy combined with Scanning Ion Mass and point Auger Electron Spectroscopies, and Back Scattering Electron Microscopy to provide extensive scientific information and understanding of Nitinol surfaces resulting after chemical, heat treatment and sterilization. 3) To use standard ASTM potentiodynamic and potentiostatic corrosion tests as well as the immersion test employing Inductively Coupled Plasma Analysis to evaluate the stability of designed surfaces and Ni release in biological media. 4) To preliminarily evaluate the biocompatibility of Nitinol surfaces by exploring blood compatibility [platelet spreading, protein adsorption, cell proliferation (peripheral blood leukocytes, THP-1 monocytes)], inflammatory mediators (expression of interlukin-1beta and tumor necrosis factors-alpha) that determine implantation outcome.
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