Biomimetic Spinning Study On Spider Silk By Silk Fibroin As A Model

Spiders have been able to spin silks for at least 380 million years. Spider silks have remarkable mechanical properties by combining high tensile strength with outstanding elongation before breaking. This combination makes many spider silks extremely tough even when compared with most high-performance synthetic materials. Spider employs simpler processing conditions and far milder than those used in synthetic fiber processing. Biomimetic spinning study on spider silk has become one of leading area in polymer science.Much work has been done in the last decade to attempt to produce man-made spider silk. There are still two key issues in these researches. One is cloning and expression of spider gene to bacteria, plant and mammal to get spider silk protein. Another is developing a proper processing to spin man-made spider silk. The recent demonstration of cloning and expression of spider presents an exciting scientific opportunity and technological chance to study on the second issue. Nowadays, there is still not enough man-made spider protein to study for us in experiments and the silkworm fibroin is very similar to spider protein. So fibroin is studied as a model system instead of spider protein in this paper.In this paper, raw B.mori silk was dissolved in LiBr-H2O system. Then the silk fibroin solution in solvent were dialyzed against de-ionized water in different equipments including regenerated cellulose membrane, inner hollow fiber membrane, Biomax flat membrane and dialysis-ultrafiltration. Method of dialysis-ultrafiltration was adopted finally for its good characteristic. It will bring benefit to purification of regenerated silk fibroin(RSF) in the near future.Rhelogical measurements were performed on a stress-controlled rheometer using a 35/l癟i cone and plate. Concentrated RSF solutions with different content of ions were studied in this experiment. There is ashear thicker from the flow curves of RSF solutions when the solutions concentrated. The viscosity of the solution becomes higher gradually while the concentration increases. After Ca2+ was added to the concentrated RSF solution, the Rheological behavior of RSF solutions was changed much. However the viscosity of the concentrated RSF solution only decreases when K+ was added.The mechanism of fiberization of RSF is discussed in this paper.There is a birefringence observed by micropolairscope in the middle division of native silk gland. The birefringence was increasing when water from the gland was vaporized. Therefore, we can predict that the process of silk spinning might be a process of liquid crystalline spinning. Moreover, Raman spectra also indicated that the secondary structure in the RSF solution has been changed to 3 -sheet by shear stress. Also, anisotropic materials were observed by micropolairscope in concentrated RSF solution when it was sheared.The structure and mechanical properties of spider silk and silkworm silk were studied in this work. The results show that the aggregative structure and mechanical properties of silk has been improved by adjusting the speed of silk spinning in order that we can get silk with eminent properties as good as spider silk. This implies that spinning process is important in biomimetic study.