Abstract: BACKGROUND: Tissue engineering scaffold transplantation is one of the most promising therapeutic methods for repairing spinal cord injury. Endogenous neural stem cells are recruited through tissue engineering scaffolds and promoted to differentiate into nerve cells to repair spinal cord injury.
OBJECTIVE: To observe the effect of transplantation of genipin crosslinked sonic hedgehog (Shh) composite fibrin scaffolds into the injured spinal cord of rats on the repair of spinal cord injury and to explore the underlying mechanism. 
METHODS: Fibrin glue, Shh composite fibrin scaffold, and genipin crosslinked Shh composite fibrin scaffold were prepared separately. In vitro degradation rate and sustained release performance of genipin crosslinked Shh composite fibrin scaffold were detected. Totally 120 female Sprague-Dawley rats were randomly divided into four groups (n=30). No material was implanted at the T10-T11 spinal cord injury site in group A. Fibrin glue was implanted in the T10-T11 spinal cord injury site of group B. T10-T11 spinal cord injury site was implanted with Shh composite fibrin scaffold in group C. Genipin crosslinked Shh composite fibrin scaffold was implanted at the T10-T11 spinal cord injury site in group D. After surgery, the rats were scored with BBB motor function every week. At 12 weeks after surgery, spinal cord tissue at and around the injury site was harvested and used for morphological observation and western blot assay. 
RESULTS AND CONCLUSION: (1) Shh composite fibrin scaffold was basically completely degraded at 14 days. The degradation rate of the genipin crosslinked fibrin scaffold at 14 days did not exceed 20%. The Shh composite fibrin scaffold basically released the Shh at 7 days. Genipin crosslinked Shh composite fibrin scaffold released Shh explosively in 1-3 days, and slowly released Shh within 4-14 days, which had a good slow-release property. (2) As time went by, the BBB scores of motor function of rats increased in each group. The BBB scores of groups B and C were higher than those of group A at 12 weeks after surgery (P < 0.05). The BBB score of group D was higher than those in groups B and C at 12 weeks after surgery (P < 0.05). (3) Hematoxylin-eosin staining showed that the recovery from spinal cord injury site in group A was the worst, and the recovery in group D was the best. (4) Immunohistochemical staining and western blot assay showed that the expression of nestin, nerve growth-associated protein 43, neurofilament protein 200, and myelin basic protein was the lowest, and the expression of glial fibrillary acidic protein was the highest in group A. The expression of nestin, nerve growth-associated protein 43, neurofilament protein 200, and myelin basic protein was the highest, and glial fibrillary acidic protein expression was the lowest in group D. (5) It is concluded that genipin crosslinked Shh composite fibrin scaffold had a good slow-release effect and could promote the repair of rat spinal cord.

Key words: genipin, sonic hedgehog, fibrin, slow-release, spinal cord injury, crosslinking, scaffolds, transplant, repair