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Computational Modeling to Predict Fatigue Behavior of NiTi Stents: What Do We Need?

Dordoni E, Petrini L, Wu W, Migliavacca F, Dubini G, Pennati G - J Funct Biomater (2015)

Bottom Line: However, their effectiveness is still debated in the clinical field.However, confidence in numerical methods is only possible after verification and validation of the models used.For the case of NiTi stents, mechanical properties are strongly dependent on the device dimensions and the whole treatments undergone during manufacturing process.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering 'Giulio Natta', Politecnico di Milano, Milan 20133, Italy. elena.dordoni@hotmail.it.

ABSTRACT
NiTi (nickel-titanium) stents are nowadays commonly used for the percutaneous treatment of peripheral arterial disease. However, their effectiveness is still debated in the clinical field. In fact a peculiar cyclic biomechanical environment is created before and after stent implantation, with the risk of device fatigue failure. An accurate study of the device fatigue behavior is of primary importance to ensure a successful stenting procedure. Regulatory authorities recognize the possibility of performing computational analyses instead of experimental tests for the assessment of medical devices. However, confidence in numerical methods is only possible after verification and validation of the models used. For the case of NiTi stents, mechanical properties are strongly dependent on the device dimensions and the whole treatments undergone during manufacturing process. Hence, special attention should be paid to the accuracy of the description of the device geometry and the material properties implementation into the numerical code, as well as to the definition of the fatigue limit. In this paper, a path for setting up an effective numerical model for NiTi stent fatigue assessment is proposed and the results of its application in a specific case study are illustrated.

No MeSH data available.


Related in: MedlinePlus

Constant life diagram for NiTi specimens for N = 107.
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jfb-06-00299-f012: Constant life diagram for NiTi specimens for N = 107.

Mentions: In the following, the results of fatigue characterization for NiTi specimens is described. The protocol was applied to 189 wires (corresponding to 21 specimens) that were tested cyclically at various combinations of mean and amplitude strain up to 107 cycles. The results were plotted as mean strain versus strain amplitude as a constant life diagram (Figure 12). In the diagram, the specimens that survived 107 cycles are shown as solid black squares, whereas those specimens that fractured are shown as open squares; the red dotted line between failure and safety points represents the fatigue strain limit for the material. The limit curve trend is coherent with literature data [14], showing two horizontal plateaus for mean strains ranging between 1%–2% and 3%–6%, and a rising line between 2% and 3% of mean strain. The results confirm the improvement of the NiTi fatigue limit for greater mean strain values, while the plateau values in terms of amplitude strain were found to be strongly dependent on surface finishing and manufacturing processes.


Computational Modeling to Predict Fatigue Behavior of NiTi Stents: What Do We Need?

Dordoni E, Petrini L, Wu W, Migliavacca F, Dubini G, Pennati G - J Funct Biomater (2015)

Constant life diagram for NiTi specimens for N = 107.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493513&req=5

jfb-06-00299-f012: Constant life diagram for NiTi specimens for N = 107.
Mentions: In the following, the results of fatigue characterization for NiTi specimens is described. The protocol was applied to 189 wires (corresponding to 21 specimens) that were tested cyclically at various combinations of mean and amplitude strain up to 107 cycles. The results were plotted as mean strain versus strain amplitude as a constant life diagram (Figure 12). In the diagram, the specimens that survived 107 cycles are shown as solid black squares, whereas those specimens that fractured are shown as open squares; the red dotted line between failure and safety points represents the fatigue strain limit for the material. The limit curve trend is coherent with literature data [14], showing two horizontal plateaus for mean strains ranging between 1%–2% and 3%–6%, and a rising line between 2% and 3% of mean strain. The results confirm the improvement of the NiTi fatigue limit for greater mean strain values, while the plateau values in terms of amplitude strain were found to be strongly dependent on surface finishing and manufacturing processes.

Bottom Line: However, their effectiveness is still debated in the clinical field.However, confidence in numerical methods is only possible after verification and validation of the models used.For the case of NiTi stents, mechanical properties are strongly dependent on the device dimensions and the whole treatments undergone during manufacturing process.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering 'Giulio Natta', Politecnico di Milano, Milan 20133, Italy. elena.dordoni@hotmail.it.

ABSTRACT
NiTi (nickel-titanium) stents are nowadays commonly used for the percutaneous treatment of peripheral arterial disease. However, their effectiveness is still debated in the clinical field. In fact a peculiar cyclic biomechanical environment is created before and after stent implantation, with the risk of device fatigue failure. An accurate study of the device fatigue behavior is of primary importance to ensure a successful stenting procedure. Regulatory authorities recognize the possibility of performing computational analyses instead of experimental tests for the assessment of medical devices. However, confidence in numerical methods is only possible after verification and validation of the models used. For the case of NiTi stents, mechanical properties are strongly dependent on the device dimensions and the whole treatments undergone during manufacturing process. Hence, special attention should be paid to the accuracy of the description of the device geometry and the material properties implementation into the numerical code, as well as to the definition of the fatigue limit. In this paper, a path for setting up an effective numerical model for NiTi stent fatigue assessment is proposed and the results of its application in a specific case study are illustrated.

No MeSH data available.


Related in: MedlinePlus