Gelation And Enzymatic Degradation Properties Of Regenerated Antheraea Pernyi Silk Fibroin

A. pernyi silk fibroin, carried with abundant sequence which exhibits specific interactions with cells, has good biocompatibility, which provides significant feasible proofs for staring A. pernyi silk fibroin-based tissue engineering scaffolds or tissue inducing materials. This paper takes a systemic research on two major basal issues of A. pernyi silk fibroin biomedical materials. One is the gelation behavior of regenerated A. pernyi silk fibroin and the structure and properties of the porous gels; the other is the in vitro enzymatic degradation behavior of regenerated A. pernyi silk fibroin porous materials.The regenerated A. pernyi silk fibroin solution was obtained via dissolving the fibers with dense inorganic salt and purifying by dialysis. We investigated the influence of environmental temperature, solution concentration, pH value and the concentration of K+ or Ca2+ on the gelation rate of regenerated silk fibroin aqueous solution and structural changes in the gels. Results indicated that gelation velocity of regenerated A. pernyi silk fibroin obviously increased with increase in solution concentration and environmental temperature. Addition of less than 5 mM Ca2+ resulted in shorter gelation time, whereas the gelation depressed when the concentration of Ca2+ was over 10 mM. Addition of less than 25 mM K+ accelerated the gelation time, whereas the promotion on gelation was weakened as the concentration of K+ was over 25 mM. By means of X-ray diffraction, FT-IR spectroscopy and Raman spectroscopy, the molecular conformation of the gels prepared from different conditions was investigated. A large amount ofβ-sheet structure was formed in the silk fibroin gel, upon gelation, the random coil/α-helix structure of the silk fibroin was significantly transformed intoβ-sheet structure. There was no obvious change in the molecular conformation of the gels with the factors of solution concentration, environmental temperature, pH value and the concentration of K+ or Ca2+.Regenerated A. pernyi silk fibroin porous materials were prepared by freeze-drying, the in vitro enzymatic degradation properties of the regenerated silk fibroin porous materials and the natural silk fibers exposed to different proteolytic enzymes ofα-chymotrypsin, collagenase-IA and protease-ⅩⅣfor various times was investigated. The facts indicated that all these three protease enzymes can degrade the porous materials, and the degradation ability ordered as protease-ⅩⅣ> collagenase-IA>α-chymotrypsin. With 1.0 U/ml proteaseⅩⅣ, the porous silk fibroin material was totally degraded within 18 days at 37℃; whereas under the same condition, the silk fiber only loss its weight of 5.6 %. It indicated that A. pernyi silk fibroin was biodegradable; the degradation speed mainly depends on its conformational structure. The degradation products were applied to Sephadex-G15 and Sephadex-G150 for separation and detection, there was abundant polypeptides in the products. We also found some free amino acids in the degradation products. The molecular conformation of the degraded A. perny silk fibroin porous materials was examined by means of X-ray diffraction, FT-IR spectroscopy, the original random coil/α-helix structure of the silk fibroin was significantly transformed intoβ-sheet structure.