Newly Developed Stent Graft with Micropored and Heparin Impregnated SPU Film. Long-Term Follow-up Study in Vivo

The use of stents has improved results after balloon carotid angioplasty. Some materials have been reported for covering the metal surface of the stent to reduce the rate of subacute thrombosis and restenosis. We have already developed a new stent graft with thin-walled controlled micropored polymer covering, and in a previous study we confirmed tissue ingrowth via the micropores at one month in a beagle model. The progress of cell migration was controlled by micropore density using a constant micropore diameter (30mum diameter, 125mum inter-pore distance). In the present study, we applied our newly developed stent graft impregnated with heparin for implantation in the rabbit carotid artery, and carried out an angiographic and histological investigation. Our stent graft was made from a Palmaz-Schatz stent and a micropored segmental polyurethane (SPU) thin film with a heparin coating. Micropores 30mum in diameter and 125mum apart were created on the thin SPU film using an excimer laser ablation technique. The surface of the micropored film was then impregnated with photosensitive gelatin that incorporated the heparin. The metal stent was rolled up and fixed to this modified SPU film under microscopic observations. These stent grafts were deployed in the common carotid arteries (CCAs) of rabbits (37 carotid arteries, 20 rabbits). The animals were sacrificed one, two and three months later, and a histological study and scanning electron microscopy study were performed for evaluation of endoluminal endothelialization and intimal thickening at the late stage. CCAs treated with stent grafts of micropored film showed poor-patency and intimal hyperplasia compared with those treated with a simple bare stent or a heparin-impregnated stent. In terms of intimal hyperplasia and patency, the heparin-impregnated stent was superior to the bare stent. Intimal hyperplasia was prevented by control of tissue ingrowth through the micropores. The antithrombogenicity of the impregnated heparin improved patency in the early stage. Our new stent graft with a heparin-impregnated SPU film thus appears promising for prevention of restenosis due to neointimal hyperplasia.