Numerical study on the effect of stent shape on suture forces in stent-grafts

Second-generation stent-grafts (SGs) have addressed many of the mechanical problems reported for first-generation endoprostheses, such as graft tear and stent rupture; however, suture wear and detachment due to pulsatile fatigue remains an issue. Numerical studies on the mechanical behavior of these endoprostheses usually model the attachment between stents and graft as a continuous ''tie'' constraint, which does not provide information on the mechanical loads acting on individual sutures. This paper presents a suitable approach for Finite Element (FE) simulations of SGs which allows for a qualitative evaluation of the loads acting on sutures. Attachment between stents and graft is modeled as rigid beams at discrete locations of the endoprostheses, and the reaction forces on the beams are analyzed. This modeling strategy is employed for four different SG models (two Z-stented commercial models and two circular-stented models) subjected to a severe 180° U-bend, followed by intraluminal pressurization. Results show that, for all models, the majority of sutures is experiencing fluctuating forces within a cardiac cycle (between 80 and 120 mmHg), which points to pulsatile fatigue as potential failure mode. In addition, the highest loads are concentrated in kinks and, for Z-stented models, at the apexes of stents. Moreover, suture loads for circular-stented models are lower than for Z-stented models, indicating better resistance to suture detachment. All these observations are in line with experimental results published in the literature, and, therefore, the procedure herein proposed may serve as a valuable tool in the development of new SG models with better suture resistance to pulsatile wear and fatigue.