Perex
NiTi alloys are routinely used as materials for cardiovascular implants in minimal invasive surgery. Fabrication of stents or occluders usually requires one or several heat treatment steps for shape-setting and adjustment of structural properties, e.g. phase transformation characteristics and temperatures. The annealing affects the bulk properties, but also the chemical composition at the surface due to the growth of an oxide layer. Consequences of the oxide layer concerning the biocompatibility of NiTi and the release of Ni are debated controversially.
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In the talk, the formation mechanism of the oxide layer on NiTi during annealing will be presented as determined by multi-stage annealing experiments using different Oxygen isotopes. Further, the mechanical stability of the respective oxide layers is assessed in situ during pseudoelastic deformation. Finally, the short- and long-term release of Nickel from the material is presented and discussed considering formation mechanism and mechanical stability of the oxide layers.