Computational studies of shape memory alloy behavior in biomedical applications

Background: Nowadays, shape memory alloys (SMAs) and in particular Ni-Ti alloys are commonly used in bioengineering applications as they join important qualities as resistance to corrosion, biocompatibility, fatigue resistance, MR compatibility, kink resistance with two unique thermo-mechanical behaviors: the shape memory effect and the pseudoelastic effect. They allow Ni-Ti devices to undergo large mechanically induced deformations and then to recover the original shape by thermal loading or simply by mechanical unloading. Method of approach: A numerical model is developed to catch the most significant SMA macroscopic thermo-mechanical properties and is implemented into a commercial finite element code to simulate the behavior of biomedical devices. Results: The comparison between experimental and numerical response of an intravascular coronary stent allows to verify the model suitability to describe pseudo-elasticity. The numerical study of a spinal vertebrae spacer, where the effects of different geometries and material characteristic temperatures are investigated, allows to verify the model suitability to describe shape memory effect. Conclusion: the results presented show the importance of computational studies in designing and optimizing new biomedical devices.