Abstract: BACKGROUND: As a biological scaffold, hydrogel has been widely used in the basic research of spinal cord injury. Based on the electrical signal conduction characteristics of spinal cord tissue, electroactive hydrogel has been preliminally explored and applied, but its efficacy and mechanism are not clear yet.
OBJECTIVE: To preliminatively explore the potential mechanism of electroactive hydrogel promoting axonal regeneration after spinal cord injury and evaluate the safety and feasibility of conductive hydrogel as biological scaffold for spinal cord injury repair.
METHODS: On the basis of methacrylated gelatin hydrogel, conductive particle polypyrrole was added to prepare electroactive hydrogel. Thirty-six adult female SD rats were randomly divided into sham operation group, model group and electroactive hydrogel group, with 12 rats in each group. Only laminectomy was performed in sham operation group. T9 spinal cord was completely transected with 2 mm defect gap in model group and electroactive hydrogel group. The defect gap was filled with electroactive hydrogel immediately after model preparation in electroactive hydrogel group. BBB score was performed on 1, 3, 7, 14 and 28 days after operation. On day 28 after operation, serum inflammatory indexes, tissue morphology of liver, spleen, kidney and spinal cord, microvascular regeneration and axon regeneration were detected.
RESULTS AND CONCLUSION: (1) BBB score of electroactive hydrogel group was better than that of model group at 28 days after operation (P < 0.05). (2) C-reactive protein levels in electroactive hydrogel group were significantly lower than those in the model group (P < 0.05). There was no significant difference in erythrocyte sedimentation rate between the two groups (P > 0.05). (3) Hematoxylin-eosin staining showed that there was no inflammatory cell infiltration in liver, spleen and kidney of rats in the three groups. Inflammatory cell infiltration was obvious at the broken end of model group; the cells were disordered and the surrounding tissues dissolved. There were fewer inflammatory cells in electroactive hydrogel group, and cells grew in the electroactive hydrogel group and arranged orderly. Masson staining indicated that a large number of collagen fibers grew into the broken end of rats in model group, while only a small amount of collagen fibers were wrapped around the electroactive hydrogel in electroactive hydrogel group. (4) Immunofluorescence staining results showed that there were fewer vascular endothelial cells and almost no mature neurons in the spinal cord defect in model group, while the vascular endothelial cells in electroactive hydrogel group were significantly more than that in model group, and there were formed vascular contours. The number of neurons was more than that in model group, but the nucleus was pyknotic compared with the sham operation group. (5) Western blot assay showed that the protein expression levels of vascular endothelial growth factor and neurofilament 200 in electroactive hydrogel group were higher than those in model group (P < 0.05). (6) Electroactive hydrogel is safe and effective as biological scaffolds to repair spinal cord injury. The mechanism of promoting axon regeneration may be related to promoting microvascular regeneration and improving microcirculation.

Key words: spinal cord injury, hydrogel, electroactive hydrogel, angiogenesis, axon regeneration, nerve repair