Clotting times and tensile properties of insoluble silk fibroin films containing heparin

Although many novel approaches for producing small-caliber arterial grafts have been developed, problems with mechanical properties and blood compatibility have up to now prevented clinical implementation. Blending anticoagulant agents with natural biomaterials having excellent cell attachment and growth properties, and making the release time of anticoagulant agents exceed the time required by endothelial tissue regeneration, might be a novel method to prepare appropriate biomaterials used in small-diameter arterial grafts. In this article, an insoluble fibroin film, having excellent blood compatibility and mechanical properties, was obtained by blending with heparin. The structural properties of the films were examined through Fourier-transform infrared attenuated total reflectance (FTIR-ATR) and X-ray diffraction (XRD). The results indicated that plentiful β-sheet crystals existed in fibroin films containing heparin. The tensile strength and elongation at break of film containing heparin were, respectively, 10.3 MPa and 54 % in the wet state, which can satisfy the mechanical requirements of blood-contacting materials such as small-diameter tubing. The clot times [activated partial thromboplastin time (APTT), thrombin time (TT) and prothrombin time (PT)] all exceeded the measurement limit of the clot detection instrument. Even the APTT and TT of film immersed in water for 28 days exceeded the measurement limit of the clot detection instrument. The in vitro culture of endothelial cells on the film was also investigated, and the result indicated that cells can grow to cover all of the available surface area of the film within 8 days. Fibroin films containing heparin could retain blood compatibility for 28 days, which means that this is a promising material for small-diameter artery applications.