Physical simulation of the random failure of implanted braided NiTi stents

0432500 - FZÚ 2015 RIV US eng J - Journal Article
Hiřmanová, Klára - Pilch, Jan - Racek, Jan - Heller, Luděk - Šittner, Petr - Recman, L. - Petrenec, M. - Sedlák, Petr
Physical simulation of the random failure of implanted braided NiTi stents.
Journal of Materials Engineering and Performance. Roč. 23, č. 7 (2014), s. 2650-2658. ISSN 1059-9495. E-ISSN 1544-1024.
[International Conference on Shape Memory and Superelastic Technologies (SMST 2013). Praha, 21.05.2013-24.05.2013]
R&D Projects: GA ČR GPP108/12/P111; GA ČR GAP107/12/0800; GA MŠMT(CZ) 7E11058
EU Projects: European Commission(XE) 262806 - SmartNets
Institutional support: RVO:68378271 ; RVO:61388998
Keywords : electron microscopy * failure analysis * mechanical testing
Subject RIV: BM - Solid Matter Physics ; Magnetism
Impact factor: 0.998, year: 2014

A problem of random clinical failures of the braided esophageal NiTi stents has been addressed by performing physical simulation experiments on helical NiTi springs loaded in cyclic tension in air, water, and simulated biological fluid. Strains and stresses involved in spring deformation were analyzed through simulation by FEM implemented SMA model. It was found that the fatigue life of NiTi springs is significantly lower in fluids than in the air pointing toward the corrosion fatigue mechanism. There is, however, a fatigue limit roughly corresponding to the onset of martensitic transformation in the wire, which is not common for corrosion fatigue. It is proposed that surface TiO2 oxide cracking plays major role in that. Once the oxide layer on the NiTi wire surface fractures, typically during the first mechanical cycle, cracks in the oxide layer periodically open and close during subsequent mechanical cycling.
Permanent Link: http://hdl.handle.net/11104/0236845