Preparation And Properties Of Bombyx Mori Silk Fibroin Materials

In this paper,silk fibroin solution was obtained by degumming,dissolving and dialysising the silkworm silk.The silk fibroin solution was added with different reagents such as 1-ethyl –(3 – dimethylaminopropyl)carbodiimide hydrochloride(EDC powder)and polyvinylpyrrolidone K30(PVP powder).The fibroin-based films and silk fibroin porous membranes were prepared by hot-air drying and freeze-drying.The properties of silk fibroin blended solutions,silk fibroin films and silk fibroin porous membranes were tested.The microstructure,quality,mechanical properties,contact angle,crystal structure and secondary structure of silk fibroin films and silk f ibroin porous membranes were investigated.And the molecular structure changes of silk fibroin were synthetically characterized.The differences of structure and properties between silk f ibroin with different preparation conditions were discussed.The conclusions were as followed:(1)The pure silk f ibroin f ilm prepared by hot air drying method was smooth and free from cracks.The surface of EDC-doped silk fibroin co-blended film was irregular and was with 100% cracks,which was related to the effects of EDC.The surface of PVP co-blended film was smooth and without surface cracks.However,there was a small amount of granular material on the surface,which was related to the incomplete dissolution of PVP and the coagulation of PVP and silk fibroin.The surface of co-blended film with EDC and PVP showed irregular undulations,and the appearance difference from the other three films was mainly due to the cross-linking reaction between silk fibroin and EDC and PVP.There were many holes in the surface of the pure silk fibroin porous membrane which was prepared by freeze-drying method,but the distribution was not uniform and the size of the pore was different.The surface of silk fibroin porous membrane obtained by adding EDC alone showed lamellar folds and there were interstices between the folds.The porosity of silk fibroin porous membrane obtained by adding PVP alone was relatively small and the size of pores were smaller compared with pure silk fibroin porous membrane.The porosity of the silk fibroin porous membrane obtained by adding EDC and PVP is relatively large,almost 100%,and the appearance was honeycomb porous structure.The pores of silk fibroin porous membranes prepared by lyophilization were irregular in shape and the size and the density of the different silk fibroin porous membranes were different.(2)In the pure silk fibroin f ilm,random coil was the main structure.The secondary structure of EDC silk fibroin blended film were random coil,?-helix and ?-sheet.The addition of EDC caused the transition of silk fibroin molecules from random coil to ?-helix.PVP regent had no effect on the conformation of silk fibroin.The addition of EDC and PVP resulted in the transition of silk fibroin molecules from random coil to ?-helix.The molecular conformation of silk fibroin porous membranes prepared by freeze-drying method was ?-helix,?-sheet and random coil coexist.The effect of EDC on the conformation of silk fibroin was more obvious.The effect of PVP on silk fibroin molecules was influenced by EDC when EDC and PVP were added simultaneous ly.Compared with silk fibroin films prepared by hot air drying,low temperature freeze drying accelerated the transformation of the amorphous structure of silk fibroin into ?-helix and ?-sheet.The change of temperature had a certain influence on the molecular structure of silk fibroin.(3)The addition of EDC destroyed the arrangement of the silk fibroin molecules and the hydrophobic residues in the protein molecules were exposed by the effect of EDC,which made the silk fibroin co-blended films more hydrophobic.PVP and EDC all hade an effect on the molecular structure of silk fibroin.The hydrophilic groups of silk fibroin were exposed by the effect of PVP and the hydrophobic groups in the silk fibroin were exposed by adding EDC,which made the different silk fibroin films showed different properties such as hydrophilic and hydrophobic.The tensile test of silk fibroin film showed that different reagents destroyed the intermolecular or intramolecular hydrogen bonds or covalent bonds in the silk fibroin membrane and accelerated the thermal motion of the silk fibroin molecules.The degree of disorder of the silk fibroin chains increased and the degree of orientation decreased,which led to the weakening of the intermolecular forces and resulted in the decrease of the breaking strength and the increase of the elongation at break.