A computational study on the effect of bending number on superelastic behavior of NiTi for medical application

NiTi self-expanding stents can be exploited in medical applications such as thoracic aortic aneurysm owing to its effects on minimizing problems such as low twistability, unsuitable dynamic performance, and inadequate radial mechanical strength. The present simulation models NiTi superelasticity based on the thermodynamics of the Helmholtz free energy (Auricchio theory) and the thermodynamics of the Gibbs free energy (Lagoudas theory). The three-dimensional nonlinear finite element method is used to evaluate the influences of bend number on the superelastic manners of new geometries designed for Z-shaped thoracic aortic aneurysm NiTi stents by the use of a radial strain (crimping) test. NiTi stents with the lowest number of bends and highest segment length showed the best mechanical performance owing to their lower chronic outward force, higher radial resistive force, and whole superelastic behavior. This numerical study can provide a suitable way of assessing the biomechanical properties of thoracic aortic aneurysm stents given the effects of geometrical parameters.