The Properties And Applications Of New Type Silk Fibers (Silk Yarn Reeled From Fresh Cocoons And Silk Fibrion Microfibers)

As a natural polymer material,silk fiber is widely used in the textile industry and biomaterials due to its excellent mechanical properties,biocompatibility and biodegradability.Silk yarn reeled from fresh cocoons and silk fibroin microfiber as two new types of silk fibers have been applied to the fields of commercial production and biomaterials.But their properties has not yet been clarified,which have affected the expansion in use.Because silk yarn reeled from fresh cocoons can significantly reduce the production cost,it is favored by reeling silk enterprises.However,due to the fact that the key properties of it are not yet clear,silk-weaving companies are unable to differentiate between silk yam reeled from fresh cocoons and dried cocoons that are circulated in the market.In the follow-up production,there is no production process for silk yarn reeled from fresh cocoons,which affects the quality of silk products.Therefore,it is imperative to study the key properties of silk yarn reeled from fresh cocoons.Similarly,we olny make sure the mechanical properties of micron-sized silk fibroin microfibers obtained by alkaline hydrolysis of degummed silk.These microfibers can be added as a mechanical reinforcement to the composite.Many studies have used silk and silk fibroin to make antibacterial materials,and the study of microfibers in the antibacterial field is still a blank.How to use the properties of silk fibroin microfibers to prepare nanosilver-based antibacterial composite materials,and the properties and applications of the composite antibacterial materials have become our research focus.This thesis consists of the following three parts.The first part is the key properties and applications of silk yarn reeded from fresh cocoons.Through the industry’s conventional equipment testing,tensile testing,appearance whiteness and microscope observation,degumming analysis,composition and structural analysis and other aspects,the key properties of silk yarn reeled from fresh cocoons is clear.Compared with dried cocoons,silk yarn reeled from fresh cocoons has more excellent mechanical properties,different surface morphology and the silk fibroin contains more β-sheet structure.The results of cross-sectional observation and sericin content indicate that the sericin coated on the surface of the silk yarn reeled from fresh cocoons does not affect its mechanical properties.The results of degumming test,tensile test and infrared analysis showed that the tensile properties of silk fibroin fibers were improved with the increase of β-sheet structures in silk fibroin of silk yarn reeled from fresh cocoons.Therefore,the mechanical properties of silk yarn reeled from fresh cocoons are obviously better than those of dried cocoons.The second part is the study of the properties and applications of silver chloride/silk fibroin microfibers composites with antimicrobial activity.Since microfibers have a high specific surface area and more amino acid side chain groups,microfibers covered with silver chloride nanoparticles are prepared by a sequential dipping method.By controlling the dipping cycles and the concentration of the reaction solutions,we can regulate the silver chloride nanoparticle size and quantity.Microscopic observation,composition and structural analysis were used to reveal the reaction mechanism and structure relationship between silver chloride nanoparticles and silk fibroin microfibers.The antibacterial activity results show that the silver chloride/silk fibroin microfibers complex possesses a broad-spectrum antibacterial activity against gram-negative bacteria(Escherichia coli and gram-positive bacteria(Staphylcoccus aureus).The third part is the study of the properties and applications of silver ion hyaluronic acid/silk fibroin microfibers composite hydrogels with antibacterial activity.By adding antibacterial agent silver ions to the mixture of hyaluronic acid derivatives and silk fibroin microfibers,a novel composite hydrogel was obtained.Through NMR,microscopy,rheological and other observation,as well as evaluation of in vitro antibacterial activity,swelling and release properties,it was clarified that hyaluronate thiol and silver ions in hydrogels were cross-linked by metallophilic attraction,at the same time these two covered the microfibers.Silver ions are not only cross-linking substances that form hydrogels,but also provide broad-spectrum antibacterial activity against gram-negative(Escherichia coli)and gram-positive(Staphylcoccus aureus)bacteria.The hydrogel can release nanosilver by dissolution and has long-lasting antibacterial activity.The results of the full-thickness skin defect model show that the composite hydrogel is an excellent wound healing biomaterial,in which the silk fibroin microfibers can reduce the inflammatory response and promote epithelialization while enhancing the overall mechanical properties of the hydrogel system.This study has analyzed the properties and applications of two new types of silk fibers,silk yarn reeled from fresh cocoons and silk fibroin microfibers.Based on the the key properties of silk yarn reeled from fresh cocoons was discovered,a method for effectively identifying the type of silk yarn was concluded.And it laid the foundation for the application of silk yarn reeled from fresh cocoons in the field of biomaterials.For the first time,silver chloride/silk fibroin microfibers composites and silver ion hyaluronic acid/silk fibroin microfibers composite hydrogels were synthesized,which expanded the applications of silk fibroin microfibers in the antibacterial field.