Abdominal aortic aneurysms are a focal dilation of the aorta which can be potentially life threatening if left untreated. Endovascular aneurysm repair (EVAR) is a noninvasive treatment that can reduce the mortality rate when compared to the standard open repair. Yet, EVAR is associated with other complications that can arise such as migration, endoleaks, or device related failures. These complications drive the need for reinterventions which have been shown to occur more frequently with EVAR than with open repair. The long term fixation and sealing characteristics of these devices is likely related to the nature of its apposition to the aortic wall. Currently there is little understanding of these mechanics and factors in how the device performs at the time of deployment. A computational model that reflects the compressive nature of an endovascular graft is beneficial in investigating these mechanics. The aims of the study are; 1) formulate an experimental methodology that captures the radial compressive nature of the stent graft, 2) develop a parameterized finite element model of the stent structure, and 3) compare the compressive behavior this model against the acquired experimental data.
A 2 mil polyethylene sleeve was used to transfer a compressive vacuum pressure from the sleeve onto 10 independent stent grafts. The loading-unloading pressure was cycled from 0 to -50 mmHg (complete collapse) over 5 minutes. A pressure transducer and optical micrometer were used to capture the vacuum pressure and diameter relationship. All ten grafts compressed in a similar elliptical shape configuration. Commercial software was leveraged to construct a parameterized model of the stent geometry. All crest and trough vertex locations of the sinusoidal stent structure were validated within 1 mm of a measured value. A dynamic quasi-static computational simulation was completed that included large deformations and contact between the sleeve and stent as well as self-contact in the sleeve. Our results show that the model is representative of the experiments and can be used to interrogate how a stent graft will perform during certain stages of deployment and immediately after deployment with some caution in regard to the stated limitations.