title: Evaluation of passive oxide layer formation-biocompatibility relationship in NiTi shape memory alloys: geometry and body location dependency.
abstract: A systematic set of ex-situ experiments were carried out on Nickel-Titanium (NiTi) shape memory alloy (SMA) in order to identify the dependence of its biocompatibility on sample geometry and body location. NiTi samples with three different geometries were immersed into three different fluids simulating different body parts. The changes observed in alloy surface and chemical content of fluids upon immersion experiments designed for four different time periods were analyzed in terms of ion release, oxide layer formation, and chemical composition of the surface layer. The results indicate that both sample geometry and immersion fluid significantly affect the alloy biocompatibility, as evidenced by the passive oxide layer formation on the alloy surface and ion release from the samples. Upon a 30 day immersion period, all three types of NiTi samples exhibited lower ion release than the critical value for clinic applications. However; a significant amount of ion release was detected in the case of gastric fluid, warranting a thorough investigation prior to utility of NiTi in gastrointestinal treatments involving long-time contact with tissue. Furthermore, certain geometries appear to be safer than the others for each fluid, providing a new set of guidelines to follow while designing implants making use of NiTi SMAs to be employed in treatments targeting specific body parts.
authors.affiliation: Koc University, Advanced Materials Group (AMG), Department of Mechanical Engineering, Sariyer, 34450 Istanbul, Turkey.
authors.forename: S M
authors.initials: SM
authors.lastname: Toker
authors.affiliation: Koc University, Advanced Materials Group (AMG), Department of Mechanical Engineering, Sariyer, 34450 Istanbul, Turkey. Electronic address: dcanadinc@ku.edu.tr.
authors.forename: D
authors.initials: D
authors.lastname: Canadinc
authors.affiliation: Leibniz Universität Hannover, Institut für Werkstoffkunde (Materials Science), An der Universität 2, 30823 Garbsen, Germany.
authors.forename: H J
authors.initials: HJ
authors.lastname: Maier
authors.affiliation: Koc University, Department of Chemistry, Sariyer, 34450 Istanbul, Turkey; Koc University Surface Science and Technology Center (KUYTAM), Sariyer, 34450 Istanbul, Turkey.
authors.forename: O
authors.initials: O
authors.lastname: Birer
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D001826:Body Fluids / Q000737:chemistry*; D007477:Ions; D057230:Limit of Detection; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000032:analysis / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission; D014025:Titanium / Q000032:analysis / Q000737:chemistry*
chemical_list: D001672:Biocompatible Materials; D007477:Ions; D010087:Oxides; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: Biocompatibility; Ion release; Microstructure; NiTi; Oxide layer; Shape memory alloy