Biomechanics of stent grafts for intracranial aneurysm repair

General non-invasive endovascular procedures for treatment of intracranial aneurysms involve stenting across the aneurysm neck, embolization and coiling of the aneurysm cavity. However it cannot be used to treat many wide-necked and fusiform intracranial aneurysms, or carotid-cavernous fistulae. Stent grafts will have the capability of completely preventing the blood flow into the aneurysm cavity or fistula rent, and thereby reducing the risk of aneurysm rupture in the brain. An endovascular approach of placing a stent graft would be a promising method [1-3]. Currently available endovascular stent graft is in big diameter and is never used in the small intracranial arteries due to the grafting techniques. In this work, we developed a new grafting technique to manufacture a small-size stent graft by capturing one kind of nonporous synthetic graft (-100 micron ultrathin) onto the commercially available metal stent as shown in Figure 1. Mechanical behavior of the stent graft is investigated through nonlinear finite element method [4]. The linear increased internal pressure is applied onto the stent to simulate the effect of balloon expansion. The obtained results as shown in Figure 2 were used to understand the effects of the graft on the mechanical behavior of the stent graft, and to predict the response of the stent graft. The interaction between the stent and the graft is simulated as non-slip contact. The 3-point bending test of the stent (Figure 3) is used to predict the flexibility of the stent, which will limit the thickness of the graft. Different graft thickness is examined to assist the design of the stent graft. The results show that a thinner cover is preferred considering the required expansion pressure from balloon, the elastic recoil of the stent graft after the unloading, and flexibility requirement. However the cover thickness must satisfy the final expansion diameter without tearing. An optimum thickness is required to balance all these requirements. This study does not include the dynamic load from the artery, which will increase the elastic recoil of the stent graft.