Finite element-based multi-phase modelling of shape memory polymer stents

In the western hemisphere almost the half of all events of death are caused by cardiovascular diseases, e.g. strokes and heart attacks. The latter are consequences of arteriosclerosis leading to abnormal deposits (plaque) in blood vessels. In order to avoid the serious symptoms discussed in the above or to hold affected blood vessels open, tubular structures made of metallic or polymeric materials (stents) are implanted. In the paper we discuss the modelling of a new kind of stents, so-called shape memory polymer (SMP) stents. The first part of the paper is devoted to the thermo-mechanical modelling of these materials. Aspects as the transition from entropy to energy elasticity are included. The constitutive equations are derived in the framework of large strains. We follow both, a purely macroscopic as well as a micromechanically motivated approach. In the second part of the work representative examples based on realistic stent structures are used to validate the model.