Histological Reactions and the In Vivo Patency Rates of Small Silk Vascular Grafts in a Canine Model

Objective: To evaluate in vivo patency rates of silk fibroin (SF) vascular grafts and resulting histological reactions in a canine model. Methods: To generate 3.5-mm inner diameter vessels, a combination of plaited silk fibers were wound with cocoon filaments and subsequently coated with an SF solution. The resulting SF grafts (n=35) were implanted into the carotid arteries of male beagles (age, 1–2 years; body weight: 9.0–10.5 kg). Expanded polytetrafluoroethylene (4-mm inner diameter, ePTFE) grafts (n=5) were used as controls. Graft patency was monitored via ultrasonography with histological changes analyzed via microscopic examination. Results: Compared with animals that received the ePTFE grafts, animals that received SF grafts exhibited the same thickness of luminal layers and fibrin accumulation and collagen fiber replacement with endothelialization at 3 months post-implantation via histological examination. The patency rates of the SF and the ePTFE grafts at 6 months post-implantation were 7.8% and 0%, respectively. Conclusion: This canine model study demonstrated that SF grafts induce unique histological reactions but fail to achieve long-term patency.