Computational Study of Axial Fatigue for Peripheral Nitinol Stents

Abstract

Despite their success as primary treatment for vascular diseases, Nitinol peripheral stents are still affected by complications related to fatigue failure. Hip and knee movements during daily activities produce large and cyclic deformations of the superficial femoral artery, that concomitant to the effects of pulsatile blood pressure, may cause fatigue failure in the stent. Fatigue failure typically occurs in cases of very extended lesions, which often require the use of two or more overlapping stents. In this study, finite element models were used to study the fatigue behavior of Nitinol stents when subjected to cyclic axial compression in different conditions. A specific commercial Nitinol stent was chosen for the analysis and subjected to cyclic axial compression typical of the femoral vascular region. Three different configurations were investigated: stent alone, stent deployed in a tube, and two overlapping stents deployed in a tube. Results confirm that stent oversizing has an influence in determining both the mean and amplitude strains induced in the stent and plays an important role in determining the fatigue response of Nitinol stents. In case of overlapping stents, numerical results suggest higher amplitude strains concentrate in the region close to the overlapping portion where the abrupt change in stiffness causes higher cyclic compression. These findings help to explain the high incidence of stent fractures observed in various clinical trials located close to the overlapping portion

Relevant Choices Affecting the Fatigue Analysis of Ni-Ti Endovascular Devices

“…Indeed, the presence of the tube plays a crucial role in affecting the initial state of the stent, albeit in a difficultly predictable way. First, it would be necessary to conduct a thorough characterization of the tube's constituent material (usually silicone or latex) for assessing its radial compliance, which is the key element in defining the equilibrium configuration at the end of the deployment [66], thus, the initial stress and strain state in the stent before cycling can be obtained [67]. Then, since remote loads are applied to the tubes, a fine calibration of the stent-tube friction properties should be addressed for a reliable description of the load quota transferred to the stent during the test.…”

Effects of Tapered-Strut Design on Fatigue Life Enhancement of Peripheral Stents

“…The conclusions showed that both types of loadings play important roles in stent fatigue fracture, depending on the implantation location within the vascular tree [ 25 ]. Meoli et al analyzed the stent fatigue performance subjected to cyclic bending and compression in the fully deployed configurations [ 26 , 27 ]. Lei et al showed that the stent-to-artery oversize ratio should be considered in the fatigue analysis of a stent [ 28 ].…”

Effect of balloon pre-dilation on performance of self-expandable nitinol stent in femoropopliteal artery

“…Advanced nonlinear FE method showed its feasibility for fatigue prediction for nitinol stents in human arteries. A series of numerical studies on the risk of fatigue failure of nitinol stents were carried out by a research team at Politecnico di Milano (Italy), with a focus on the effects of failure criteria, loading conditions and plaque morphology (Petrini et al 2012(Petrini et al , 2016Meoli et al 2013Meoli et al , 2014Dordoni et al 2014;Allegretti et al 2018). Lei et al (2019) showed both atherosclerotic plaque and physiological loading conditions should be considered to accurately assess the fatigue behaviours of stents.…”