Long-term patency of small-diameter vascular graft made from fibroin, a silk-based biodegradable material

Objective: There is an increasing need for vascular grafts in the field of surgical revascularization. However, smaller vascular grafts made front synthetic biomaterials, particularly those <5 mm in diameter, are associated with a high incidence of thrombosis. Fibroin is a biodegradable protein derived from silk. Silk fibroin from Bombyx mori provides an antithrombotic surface and serves as a scaffold for various cell types in tissue engineering. We evaluated the potential of fibroin to generate a vascular prosthesis for small arteries. Methods. A small vessel with three layers was woven from silk fibroin thread. These fibroin-based grafts (1.5 turn diameter, 10 mm length) were implanted into the abdominal aorta of 10- to 14-week-old male Sprague-Dawley rats by end-to-end anastomosis. Polytetrafluoroethylene (PTFE)-based grafts were used as the control. To investigate the origin of the cells in the neointima and media, bone marrow transplantation was performed from green fluorescent protein (GFP) rats to wild-type rats. Results. The patency of fibroin grafts at I year after implantation was significantly higher than that of PTFE grafts (85.1% vs 30%, P<.01). Endothelial cells and smooth muscle cells (SMCs) migrated into the fibroin graft early after implantation and became organized into endothelial and medial layers, as determined by anti-CD31 and anti-alpha-smooth muscle actin immunostaining. The total number of SMCs increased 1.6-fold from I month to 3 months. Vasa vasorum also formed in the adventitia. Sirius red staining of the fibroin grafts revealed that the content of collagen significantly increased at I year after implantation, with a decrease in fibroin content. GFP-positive cells contributed to organization of a smooth muscle layer. Conclusions: Small-diameter fibroin-based vascular grafts have excellent long-term patency. Bone marrow-derived cells contribute to vascular remodeling after graft implantation. Fibroin might be a promising material to engineer vascular prostheses for small arteries. (J Vasc Surg 2010;51:155-64.) Clinical Relevance: The present study evaluated the efficacy of a fibroin, a new silk-based biodegradable material, to generate small diameter grafts. When implanted in rat abdominal aorta, a fibroin-based graft (1.5 mm in diameter) showed excellent long-term patency, with optimal mechanical properties. Endothelial cells and smooth muscle cells migrated into the fibroin graft early after implantation and became organized into endothelial and medial layers, generating a vascular-like structure. Our findings suggest that a silk fibroin might be a promising material to develop vascular prostheses for smaller arteries.