Dynamic seal at the aortic neck-endograft interface studied using a novel method of cohesive zone modeling

Endovascular aortic stent graft technology radically altered aortic aneurysm repair from a maximally invasive procedure to a minimally invasive approach. Whereas the overall principle of the repair remained the same, the surgeon ceded control of the proximal seal when suturing was eliminated. In endovascular aneurysm repair (EVAR), no longer does the surgeon control the precise placement of mechanical fasteners (sutures) between graft and tissue; rather, the graft is kept in place by creation of a seal zone that often lacks any mechanical fastening. The kinematic coupling condition is replaced by contact mechanics between the outer graft surface and the aorta.

We develop a novel computational methodology to fully model and characterize the aorta-endograft seal zone within a fully integrated aorta-EVAR model. The aorta, endograft, and intraluminal thrombus are modeled by standard finite element analysis in the limit of elastic response under pressure loading conditions. The seal zone in our simulations is fully dynamic and modeled using the cohesive zone method. Our methodology allows full separation of the aorta and endograft, simulating loss of seal and endoleak.

Using patient-specific geometry, we show that our approach is capable of predicting the location of rupture in an index patient who presented with a ruptured juxtarenal aneurysm. Applying our novel cohesive zone method analysis to the post-EVAR geometry, we studied the stability of the endograft under several seal zone strengths correlating to very weak, standard, and very strong seal. Loss of seal is shown to correlate to the propagation of an elastic front in the aortic neck. We propose that aortic neck dilation, which develops from graft deployment and pressurization, provides an energy release mechanism that drives seal zone failure: the elasto-adhesive seal model.

We develop the first ever fully integrated computational model of aorta-endograft seal. Our elasto-adhesive seal model provides the first biomechanical model to evaluate seal loss. We hope that our method will provide a rich tool set with which to study the vexing problems of type I endoleak and help guide the development of technologies to optimize seal.