Development of microporous self-expanding stent grafts for treating cerebral aneurysms: designing micropores to control intimal hyperplasia

Abstract

Treatment of large (diameter 12-25 mm) or giant (diameter >25 mm) cerebral aneurysms with a broad neck in the cranio-cervical area is difficult and carries relatively high risks, even with surgical and/or endovascular methods. To this end, we have been developing a high-performance, self-expanding stent graft which consists of a commercially available NiTi stent (diameter 5 mm, length 20 mm) initially covered with a thin microporous segmented polyurethane membrane fabricated by the dip-coating method. Micropores are then created by the excimer laser ablation technique, and the outer surface is coated with argatroban. There are 2 types of micropore patterns: circular-shaped pore type (pore: diameter 100 μm, opening ratio 12.6%) and the bale-shaped pore type (pore: size 100 × 268 μm, opening ratio 23.6%). This self-expanding stent graft was tested on side-wall aneurysms of both canine carotid arteries that were experimentally induced using the venous pouches from the external jugular veins, with the self-expanding stent graft on one side and a bare self-expanding stent on the other side. All carotid arteries were patent and free of marked stenosis after 1 month. All aneurysms were occluded by stent grafts, while patent in those treated with bare stents. Histologically, the stent grafts with bale-shaped micropores and a high opening ratio were associated with less intimal hyperplasia (187 ± 98 μm) than the bare stents (341 ± 146 μm) or the stent grafts with circular micropores and a low opening ratio (441 ± 129 μm). A pore ratio of 23.6% was found to control intimal growth.