S. Harvey, MSC Software Corp., Santa Ana, CA
Nitinol self-expanding stents are used to treat peripheral occluded vessels such as the superficial femoral artery or the carotid. The complex vessel articulation requires a stent device that is flexible and kink resistant yet durable. The present study shows how the latest advances in commercially available engineering software tools along with multi-threaded finite element solver technology permit engineering simulations of the many aspects of the Nitinol stent design that were not possible in the past. Specifically in this study the flat pattern stent geometry is automatically meshed and rolled. The stent is then expanded, shape set to a specified diameter, crimped inside a delivery device and positioned inside a realistic tortuous artery. The stent Nitinol superelastic material model is based on the work of Auricchio, and a hyperelastic material model is used to represent the artery. With the stent positioned the delivery device sheath is retracted deploying the device against the artery wall. Alternating diastolic to systolic pressures are applied to the vessel wall and the stress history is extracted for all regions of the finite element stent model for fatigue evaluation on a modified Goodman diagram. Additionally, the vessel is articulated resulting in bending, extension/compression, and twisting of the stented artery, and the fatigue life prediction of the stent is repeated. Throughout the finite element simulations, the stress time history at all points in the stent is maintained. The results show that advanced engineering finite element simulations of the Nitinol stent are possible today inside realistic simulated human arteries.
Summary: Comprehensive Nitinol stent finite element numerical simulations: from shape setting and deployment, through fatigue life predictions in a realistic peripheral human artery subjected to pulsatile and articulation loading conditions.
