Self-assembling Of Silk Fibroin And Its Application In Biomedicine

Silk has been in practically used by man for centuries mainly because of its unique luster, fineness, and mechanical properties. In recent years, extensive studies have been carried on the application of silk fibroin (SF) for non-textile uses. SF is a kind of protein, therefore, silk and silk fibroin can be used as biomaterials, e.g. surgical suture, wound covering material, soft contact lens, scaffold for tissue engineering, and controlled release carrier, etc., because it shows both impressive biocompatibility and biodegradability.It is well known that silk fibroin can be processed into various forms including gels, powders, fibres and membranes(films), which are more convenient for various applications. However, there were few reports concerning the micro-and nanoparticles which had promising application in the field of controlled release and gene engineering, etc., due to their controlled release characteristics and excellent biocompatibility.Self-assembly of polymer chains to nano-materials is one of the most active research areas. This relates to the general area of protein self-assembling which is important because many human diseases are related to protein misfolding.In the present work, we report a new approach to prepare protein-based nanospheres and porous scaffolds based on regenerated silk fibroin self-assembling in specific conditions. The primary application of silk fibroin nanospheres and porous scaffolds are in biomedical areas, such as controlled release, artificial skin and nerve generation conduit, etc.In the first section, we reported the preparation of SF nanospheres by self-assembling of silk fibroin in aqueous solution with a small amount of ethanol. The preparation process did not use any toxic organic solvents or cross-linkers, such as glutaraldehyde, as the residues of these compounds in the products are unfavorable for practically clinical use. The produced nanospheres were all in a fine spherical shape with rough surfaces and without any aggregation or adhesion. The nanospheres after lyophilization did not aggregate and could be easily dispersed in distilled water again. The present study showed that SF nanospheres can be prepared with predictable and reproducible size, in a controllability size range from 200 to 1000nm, by a mild self-assembling. The ethanol additives, freezing temperature and silk fibroin concentration had obvious effect on particle size and size distribution. Particle sizedecreased with the addition of more ethanol over a narrow range.SF porous scaffolds were fabricated using a novel method, namely biomacromolecular self-assemby. SF porous scaffolds were prepared by a technique integrating mixed solution casting and protein conformational transition under specific conditions. With this technique, we were able to prepare SF porous scaffolds with high mechanical strength and controllable porous structure. Scaffolds with different geometrical shapes can be prepared depending on the geometries of moulds only. The prepared porous scaffolds were highly porous with a porosity range of 85～98%, and a controllable pore size of 10～350μm, with tensile strength up to 750 KPa, elongation to break to maximum 70%, and the Young's modulus of 1．9～8．9 MPa, which meets the general requirements of tissue engineering. The porous scaffold had an interconnected open-pore microstructure. It is possible to control the above-mentioned structural parameters of SF porous scaffolds and their physical properties such as mechanical properties for different applications by adjusting the silk fibroin concentration, n-butanol additives, and freezing temperature. In this way, SF porous scaffolds can be produced under very mild conditions without using any special production apparatus, surfactants, initiator, crosslinking agent, and toxic organic reagent with the related a fear of adversely affecting the living body.Based on the work mentioned above, we alse investigated the possibility of silk fibroin nanospheres and porous scaffolds in biomedical areas applications. 5-FU-loaded SF nanospheres and porous scaffolds were prepared by SF self-assembly. Drug release, which was investigated in PBS at physiological conditions, was high at the initial period and almost reached to a constant rate subsequently. The magnetic nanospheres have some magnetic response and can directly moved toward the magnetic field. In addition, we had tried to prepare several kinds of multiple layers artificial skin scaffolds, which has special double deck structure similar to natural skin, based on the study of porous scaffolds.Moreover, the biocompatibility investigation, Schwann Cell (SC) culture and nerve generation conduit animal experiment was also involved in this work. Investigation results show that the SF porous scaffolds have excellent biocompatibility and can be biodegradable but need a longer period, cells and capillary vessel implanted can be observed. The SC can grow very well after it was replanted into porous scaffolds. The SF porous nerve regeneration conduit hold great promise for the regeneration of peripheral nerve and other tissues which require tubular scaffolds such as long bone, intestine, or blood vessel.