Seal Zone Mechanics: Mechanical Stability of the Endograft/Aorta Interface

Endovascular surgery (EVAR) has nearly replaced open aortic aneurysm repair. The long-term stability of EVAR repairs has come into question especially concerning graft endoleaks. Adhesion between the endograft and aortic wall is poorly understood and differs substantially from the traditional approach of kinematic fastening (suturing) utilized in open reconstructions. We provide a first general computational and theoretical approach to characterize and study seal zone mechanics. Our analysis (computational and analytical) shows that in the limit of no adhesion (or very weak adhesion) the endograft is always unstable relative to its position in the non-aneurysmal aorta. The energy driving graft displacement is the stored elastic energy in the aortic wall that comes from the oversizing of the stent graft. Adhesion between the aorta and endograft balances this stored elastic energy. This balance of adhesive energy to elastic energy is the central control parameter in the stability of the endograft. We develop a toy model for graft stability and apply it to patient specific geometries. Our work provides the first steps towards a robust physical understanding of the mechanics involved in EVAR stability that will allow for more durable future devices.