Biomimetic Spinning Study On Silk Fibroin Solution

In this thesis, the development of biomimetic spider and silkworm silk has been briefly introduced. The processes and properties of resultant man-made silk fiber have also been summarized. It is found two key issues are not discussed yet. Whether the conformation of silk fibroin in regenerated solution or in the silkworm gland is the same or not? Whether it is necessary to prepare the spinning solution by a biomimetic process? In our work, silk fibroin of silkworm is selected as a model system because there is still not enough spider silk protein that can be supplied to do spinning and on the other side, the composition of silkworm fibroin is very similar to spider protein. In order to answer the above questions, the concentrated regenerated silk fibroin aqueous solution was prepared first, it's structure and properties of rheology and flow stability were studied. After that, the electrospin process was applied on regenerated concentrated silk fibroin aqueous solution in order to find out the conditions to form silk fiber from silk fibroin aqueous solution. It is found a kind of silk fiber can be got, but the structure of this kind silk fiber is between amorphous film and nature silk. The difference between the structure and properties of silk fibroin in regenerated aqueous solution and in vivo was further studied. The main conclusions are as follows.Viscous, transparent, homogeneous and spinnable silk fibroin aqueous solutions with high silk fibroin content were first prepared. The rheological behaviors of solutions with different concentration were studied by HAAKE RS150 rheometer. There is a rapid initial shear thinning at low shear rates (<10 s-1) for regenerated silk fibroin aqueous solutions with low concentration. However, the shear-thinning phenomenon becomes not obvious with the increase of the solution concentration, which is different from ordinary polymer solution. With the increase of concentration, the macromolecule chain become more and more compacted, the entanglements in solution increase not very quickly. As a result, the viscosity of solution is not very high.The zero shear viscosity is increasing with the concentration of regenerated silk fibroin aqueous solution and reaches max in 35%, then decreases. But all these solutions are isotropic. Only with shear the solution becomes anisotropic. With the increase ofconcentration, the birefringent or anisotropic phenomenon becomes easier under the same shear rate. Similarly, with the same concentration, the anisotropic phenomenon becomes more and more obvious with the increase of shear rate. Raman spectroscopy analysis showed that the structure of silk fibroin has changed from random coil and/or a helix into β-sheet by shear.The study on the flow stability of regenerated silk fibroin aqueous solutions with different concentrations under different temperatures indicates that the flow stability decreases quickly with the increase of solution concentration and temperature. X-ray diffraction, Fourier transform infrared (FTIR) and Raman spectroscopy analysis show that silk fibroin in regenerated aqueous solution is mainly in random coil conformation. However, it turns into a helix and p-sheet conformation after gelation, and both silk I and silk II structure appears accordingly. The key concentration and key temperature for the flow stability of regenerated silk fibroin aqueous solution are about 27wt% and 25°C, respectively. Silkworms in the nature may possibly make full use of this rule. The investigation implies that the original dilute regenerated or recombinant silk fibroin aqueous solution should be stored under low temperature and concentrated just before spinning.By using electrospinning technique, beaded, cylinder shaped or ribbon like ultra-fine silk fibroin fibers are obtained from regenerated concentrated silk fibroin aqueous solution under different processing conditions. These fibers have an average diameter of 700 nm. It is found that the morphology and the secondary structure of the as-spun silk fibroin fibers are strongly influenced by the...