Finite element analyses of in vivo fatigue behavior of peripheral stents: effect of plaque features.

Fatigue resistance of Nitinol peripheral stents implanted into femoropopliteal arteries is a critical issue due to the particular biomechanical environment of this district. Hip and knee joint movements associated with patient’ daily activities expose the superficial femoral artery, and therefore the implanted stents, to large and cyclic deformations. These loadings, combined with the cyclic loading due to the arterial blood pressure, may cause fatigue fracture of stents. The stress/strain field throughout the stent is likely affected by plaque features. In this study, finite element simulations of angioplasty, stenting and subsequent in vivo loading conditions (cyclic pressure and axial compression) have been developed in different stenotic vessel models. A model of a stent, resembling the geometry of a commercial peripheral stent, has been reconstructed. A parametric model of stenotic artery has been developed, described by vessel inner diameter, obstruction ratio, length, plaque asymmetry and sharpness. The results, analyzed in terms of amplitudes (ε1a) and mean values (ε1m) of the first principal strain through the stent, showed that: i) cyclic pressure effects are negligible if compared with axial compression ones; ii) replicating a realistic vessel morphology is fundamental, since plaque features affect fatigue resistance of the stent with the same loading conditions.