Preparation And In-vitro Twisting And Bending Fatigue Simulation Of Stent-grafts

Aneurysm is a common disease in clinical practice. Compared with traditional open surgery,there are incomparable advantages of endovascular aortic repair (EVAR) in aortic aneurysmtreatment. Long-term complications after endovascular aortic repair (EVAR) includingvasodilatation, endoleaks, pseudoaneurysm and aneurysm rupture arise from a defect in thestent-graft (SG).This paper was intended to weave different structural grafts under the same conditions. Also,different stent angles of SG were designed and tested in a long-term in vitro buckling and twistingfatigue simulation device to investigate the fatigue performance. The non-destructive (grossobservations) and destructive (fabric characteristics, mechanical properties) properties wereanalyzed. At the same time, ABAQUS software was used to model and analyze mechanicalsimulations in a variety of loads.The result showed that there were aging damages in all the SG test specimens, includingbreakage of zigzag stents, abrasion of the sutures and damage of the grafts. As the testing timeprolonged, the fatigue performance of SG was aggravated. For the same type of stent, the SGfitted with plain weave structure showed a considerably lower endurance compared to those fittedwith twill weave structure due to higher strength of the exposed warp yarns. For the same type ofweave structure, the SG fitted with angle of35degree zigzag stent was more easily to fatiguecompared to stent of45degree. Because the smaller the angle of zigzag stent, the smaller ofstressed area acting on the graft, which was more prone to stress concentration that caused severedamage to the SG specimens.According to the non-parametric test analysis of SPSS software, the thread count, thickness,surface density, porosity, filament diameter and strength of the weft monofilaments of the agedSG supported with same stents but different structural grafts showed a significant level of P≤0.05,which meant that there were significant differences among three different weave structures. Also,to the SG supported with the same weave structure but different stent angles, there was asignificant level of P>0.05of the properties of warp thread count, thickness, filament diameter andstrength of the weft monofilaments of the SG fitted with plain weave structure, which meant theinfluence of different stent angles to the fatigue performance of the plain weave SG was notnotable. But the others are appreciable.It can be seen in ABAQUS software mechanics simulation models, there were significantdifferences in SG under three different loads (twisting, bending, synchronously twisting andbending). The stress nephogram showed that there is noticeable stress concentration in of the90° benting and the proximal positions of SG samples, which were the weak areas of SG. Also, largedeformation of proximal of SG could be seen in the displacement nephogram. Mechanical modelsimulation analysis not only provideed theoretical support for the failure of SG devices in in-vitrotwisting and bending fatigue tests, but also gave a scientific and practical basis for the design andimprovement of SG.