Smart silk sutures with double network structures

Abstract

Biomedical textiles and fiber-based implants have attracted tremendous attention in recent years. Silk fibers are recognized as valuable starting materials for apparel manufacturing in the textile industry and modern suture products due to their bright luster, high strength, and good biocompatibility, despite the competition from synthetic fibers. In particular, silk sutures remain an essential type among modern surgical sutures. However, there are two main issues for current silk sutures. First, silk sutures easily attract microbes and have no antibacterial ability, which limits their continuous application to avoid bacterial infections. Second, silk sutures suffer from mechanical weakness in the wet state, which presents a potential risk for suture application in bio-tissues where a high tension exists. To address these issues, this thesis focuses on the design and fabrication of tough and antibacterial silk sutures. To alleviate the wet weakening problem, firstly, fibroin fibers (FFs) were directly cross-linked by employing a ruthenium-mediated redox pair under visible light at room temperature for the first time. The resultant cross-link density of fibers was calculated based on their swelling ratio evaluation in LiBr solution. Further applying stretch to the fibers during irradiation increased the fiber strength to higher values. The break stress and Young's modulus of photo-cross-linked 15% stretch FFs reached a 60−90% increase in comparison to the original FFs in dry and wet conditions. Additionally, double network (DN) structures were produced via the fast photo-initiated synthesis in solid FFs after swelling for further strength enhancement. These DN FFs were characterized with respect to morphology, secondary structure, alkali resistance, and tensile property. The break stress of resultant DN FFs for 5 min irradiation reached over 80% increase in both dry and wet conditions. Furthermore, polydiacetylenes were combined with silk sutures for bacteria sensing via chromatic response. Subsequently, the cationic guanidine-containing copolymer was synthesized, exhibiting biocidal activity against Gram-positive S. aureus and Gram-negative E. coli with up to a 99.999% reduction. The antibacterial mechanism of this cationic copolymer was also explored. Moreover, guanidine-containing DN silk sutures were fabricated via photo-polymerization based on this antibacterial guanidine-containing copolymer. These guanidine-containing DN silk sutures showed biocidal properties against S. aureus and E. coli and strength superior to the commercial product in both dry and wet environments for surgical suture application. In summary, a tough and antibacterial silk suture was fabricated by photochemical reactions to solve these major issues for present silk sutures and fill up the gap in its surgical suture application. This work provides a new approach to manufacture antibacterial sutures and explores the relationship between the double network structures and the tensile property of modified fibers. This methodology could be applied to a variety of polymers and extended to more functional enhancements with expectable sustainability at an industrial scale.