Preparation And Characterization Of Spongy Hydrogels From Aqueous Bombyx Mori Sericin

Sericin is an excellent natural protein which has the potential of application in medical and pharmaceutical field for its anti-cancer, immobilization and cell growth acceleration etc. In order to process sericin into applicable form as medical biomaterials, many groups have focused on development of hydrogel from sericin. Though the mechanical property of sericin hydrogel has usually be improved by adding functional cross-linkers, the toxicity of the hydrogel may be enhanced. Therefore, we attempt to develop spongy hydrogel from aqueous Bombyx mori sericin by using a freeze-thawing method without any cross-linking reagent.In order to get a suitable sericin to prepare spongy hydrogel, various sericin with different molecular weight were studied. And the gelation ratio of aqueous sericin and characteristics of spongy hydrogel at different frozen conditions were compared to optimize preparation condition.The structure and properties of sericin with different molecular weight were shown in chapter 2. Sericin with different molecular weight were extracted through two hot water method and further bathed at different temperature for various time. SDS-PAGE(sodium dodecyl sulfate-polyacrylamide gel electrophoresis) results show that the molecular weight of sericin extracted with boiling-water is larger and concentrated than that extracted with high temperature and pressure method. The higher temperature and longer time, the lower molecular weight of sericin obtained. The gelation of sericin at 4℃,15℃and 25℃revealed that whether bathed at high temperature or not, that of sericin extracted with boiling-water is always slower than that extracted with another method. FTIR(fourier transform infrared spectroscopy) and DSC(differential scanning calorimetry) results indicated that both random coil and crystal structure existed in sericin extracted with two method with bath treatment or not.The gelation ratio of sericin at different frozen condition was measured in chapter 3. The results show that the gelation ratio is not remarkably affected by frozen conditions of sericin concentration, frozen temperature, frozen time and frozen-thawed repetition. Sericin extracted with boiling-water show little lower gelation ratio than that obtained with high temperature and pressure method. The frozen gelation ratio of sericin extracted with two method decline with the bath temperature and time.In chapter 4, the structure of spongy hydrogel prepared at different frozen condition were characterized. The pore shape and diameter of hydrogel prepared from different sericin concentration or at different temperature differ significantly according to the SEM(scanning electron microscope) images. The porosity and the maximal water absorption of sericin hydrogel determined with water displacement method is different mainly referring to sericin concentration. Nevertheless, the density of hydrogel is little affected by preparation conditions. FTIR, XRD(X-ray diffraction) and DSC curves indicate that the hydrogel adopt mainly random coil conformation.The water absorption, retention, solubility, mechanical property and cell toxicity of various sericin hydrogel were determined in chapter 5. Sericin concentration is the main factor affected the water absorption and retention of hydrogel. The hydrogel show higher solubility with temperature and time. The compression modulus detected indicated that the swelling hydrogel have excellent flexility and restore property. The L-929 cell was used to test the toxicity of sericin hydrogel washed with distilled water or not after frozen-thawed. The culture extract solution of hydrogel not washed with distilled water at the concentration of 100% display the 2 grade toxicity, however, the biocompatibility is improved after washed with distilled water.Chapter 6 summarized the main conclusion. The boiling-water method was selected to extract sericin from cocoons. A spongy hydrogel with high flexility was developed from Bombyx Mori sericin with a safe and environmental way. The optimal conditions for hydrogel preparation is to freeze aqueous sericin at the concentration higher than 3% at-20℃for 3h with once frozen-thawed repetition.