Fatigue behaviour of Nitinol peripheral stent: finite element analyses of in vivo loading conditions

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, combined with the cyclic loading due to the arterial blood pressure, expose the superficial femoral artery (SFA), and therefore the implanted stents, to quite large and cyclic deformations that may influence the fatigue resistance of the device. In this study, simulations of angioplasty, stenting and subsequent in vivo loading conditions (cyclic pressure, axial compression and bending) have been developed in a stenotic vessel models, using the commercial code ANSYS (Ansys Inc., Canonsburg, PA, USA). A finite element model of a stent, resembling the geometry of the Maris Plus peripheral stent (Medtronic-Invatec), has been reconstructed. A stenotic vessel model has been developed. The results, analyzed in terms of amplitudes (ε1a) and mean values (ε1m) of the first principal strain through the stent, showed that the cyclic pressure is the less critical loading condition: the maximum alternating strain in this case is one order lower than in others loading conditions. Moreover, this study reveals the importance of replicating a realistic vessel morphology, since plaque shape could affect fatigue resistance of the stent.