title: Effect of thermomechanical pre-treatment on short- and long-term Ni release from biomedical NiTi.
abstract: The effect of annealing and deformation on short-term (21days) and long-term (8months) Ni release from biomedical NiTi wires is studied. The deformation of annealed NiTi wires causes cracking and flaking of the surface oxide layer. Flaking of oxide particles does not uncover the Ni-rich layer underneath the surface oxide layer, since at sites where flaking occurs, a thin (∼25nm) layer of oxide remains on top of this Ni-rich layer. The number of cracks in the oxide and Ni-rich layer, respectively, increases with deformation, and intercrystalline crack propagation into the Ni-rich layer and the NiTi bulk is observed. In plastically deformed wires, the cracks may remain opened, providing access of immersion liquid to these zones. Characteristics and quantity of short-term Ni release are significantly affected by the pre-deformation, resulting in an up to 2 times higher total Ni release within the first 21days of deformed compared to annealed wires. Pre-deformation does not significantly influence long-term Ni release; all annealed and deformed samples exhibit similar long-term Ni release rates. The source of Ni during short-term release is the Ni contained in the surface zone of the oxide layer. For high pre-deformation, the Ni-rich layer is a second source for Ni. This second source is also the cause for Ni release in long-term immersion experiments.
authors.affiliation: Otto Schott Institute of Materials Research, Metallic Materials, Friedrich Schiller University, Löbdergraben 32, 07743 Jena, Germany.
authors.forename: Katharina E
authors.initials: KE
authors.lastname: Freiberg
authors.affiliation: Institute for Clinical Chemistry and Laboratory Medicine, Jena University Hospital, Friedrich Schiller University, Erlanger Allee 101, 07747 Jena, Germany.
authors.forename: Sibylle
authors.initials: S
authors.lastname: Bremer-Streck
authors.affiliation: Institute for Clinical Chemistry and Laboratory Medicine, Jena University Hospital, Friedrich Schiller University, Erlanger Allee 101, 07747 Jena, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Kiehntopf
authors.affiliation: Otto Schott Institute of Materials Research, Metallic Materials, Friedrich Schiller University, Löbdergraben 32, 07743 Jena, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Rettenmayr
authors.affiliation: Otto Schott Institute of Materials Research, Metallic Materials, Friedrich Schiller University, Löbdergraben 32, 07743 Jena, Germany. Electronic address: Andreas.Undisz@uni-jena.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Undisz
mesh_terms: D000497:Alloys / Q000737:chemistry*; D001672:Biocompatible Materials / Q000737:chemistry*; D055595:Mechanical Phenomena; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D009532:Nickel / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014025:Titanium / Q000737:chemistry*
chemical_list: D000497:Alloys; D001672:Biocompatible Materials; D010087:Oxides; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: Minimal invasive application; NiTi alloy; Pseudoelastic deformation; Short-term/long-term Ni release; TEM