BACKGROUND: The molecular weight of fibroin is inevitably reduced in the course of the dissolution of regenerated fibroin fiber, and this is why we have not entered the stage of the practical application of the regenerated fibroin fiber till now.OBJECTIVE: To obtain biodegradable regenerated fibroin fiber.DESIGN: A single sample experiment.SETTING: Jiangsu Provincial Key Laboratory of Silk Project of Material Engineering College of Soochow University.MATERIALS: Leftover silk pieces were provided by Suzhou Silk Import & Export Corp.METHODS: This study was performed at Jiangsu Provincial Key Laboratory of Silk Project of Material Engineering College of Suzhou University between January 2003 and December 2004. By controlling the molecular of abandoned natural fibroin fiber during neutral salt dissolution process, wet spinning technique and draft method were applied to spin regenerated fibroin fibers that have certain mechanical and biodegradable properties.The specific procedure is as follows: ①fibroin preparations. ② Spinning solution preparations. ③ Regenerated fibroin fibers were spun with wet spinning method. ④Sodium lauryl sulphate-polyacrylamide gel electrophoresis method was used to detect the molecular weight of LiBr dissolved fibroin solution. ⑤To detect the crystallinity and orientation of fibroin fibers. ⑥ To detect the mechanic properties of regenerated fibroin fibers. ⑦ To detect the in vitro enzyme degradation rate of fibroin fibers.MAIN OUTCOME MEASURES: ①The relative molecular weight of LiBr dissolved silk fibroin. ② Result of X-Ray diffraction. ③The in vitro enzyme degradation rate of regenerated fibroin fibers.RESULTS: ①After LiBr dissolution, the molecular weight of fibroin spinning solution was mainly below 100 000. ②During the coagulation and pulling process of regenerated fibroin fiber wet spinning, fibroin fiber conformation changed from random convolution to the co-existence of β-folding and random coi1/α-spiral conformation in molecular chain. ③ Actinozyme was used to assess the in vitro enzyme degradation rate of hexafluoroisopropanol spun regenerated silk fibroin, and the 30 day-degradation rate of regenerated fibroin fibers was 37.16%, compared with 10.70% of natural fibroin fiber.CONCLUSION: Wet spinning technique and draft method can be used to spin regenerated fibroin fibers possessing certain mechanical and biodegradable properties by controlling the molecular weight of abandoned natural fibroin fibers during neutral salt dissolution process.

Objective To investigate the effect of porous silk fibroin scaffolds (PSFSs) combined with chondroitinase ABC (ChABC)for treatment of rats with spinal cord injury (SCI).Methods After exposed to T9 spinal cord transection injury,96 SD rats were divided into control group,PSFSs group,ChABC group,and PSFSs plus ChABC group according to random number table.BBB scoring system was used to evaluate hindlimb motor function in rats.Immunohistochemistry and Western blot analysis were performed to detect expression levels of neurofilament-200 (NF-200),glial fibrillary acidic protein (GFAP),and growth associated protein-43 (GAP-43) of the injured spinal cord.Immuno-fluorescence staining was carried out to evaluate regeneration of nerve fiber.Results BBB score improved in PSFSs group (8.1 ± 0.8),ChABC group (9.0 ± 1.1),and PSFSs plus ChABC group (13.7 ± 1.3) compared with control group 4 weeks after injury (5.3 ±0.7,P ＜0.05).Immunohistochemistry showed higher integral absorbance (IA) values of NF-200 and GAP-43 in those treatment groups,but smaller GFAP-positive area was observed compared with control group (P ＜ 0.05).Immuno-fluorescence staining indicated more GAP-43 growth at injury sites in PSFSs plus ChABC group in contrast with other 3 groups.Western blotting showed levels of NF-200,GFAP,and GAP-43 differed among groups (P ＜ 0.05).Conclusion PSFSs combined with chondroitinase ABC transplantation can enhance axonal regeneration,inhibit glial scar proliferation and hence promote motor function recovery.