Abstract: BACKGROUND:  The repair of peripheral nerve defects by nerve conduit bridging can provide a suitable microenvironment for nerve regeneration. On one hand, it can provide a unique channel for nerve regeneration, prevent the invasion of peripheral connective tissue and the formation of scars. On the other hand, it can maintain endogenous and exogenous neurotrophic factors, growth factors and other stimulants to promote axon growth.
OBJECTIVE: To observe the therapeutic effect of chitosan/polyvinyl alcohol catheter injected with brain-derived neurotrophic factor sustained-release microspheres to bridge peripheral nerve defects.
METHODS: Chitosan/polyvinyl alcohol nerve conduit was prepared by repeated freeze-thaw technique. The brain-derived neurotrophic factor microspheres were obtained by polymer-alloys combined with oil-oil emulsion/solvent evaporation method. A 15 mm sciatic nerve defect model was made in the right hindlimb of 60 adult male Sprague-Dawley rats. They were selected and randomly divided into four groups (n=15 per group): group A implanted with autogenous sciatic nerve; group B implanted with chitosan/polyvinyl alcohol nerve catheter, injected with normal saline; group C implanted with chitosan/polyvinyl alcohol nerve catheter, injected with brain-derived neurotrophic factor solution; group D implanted with chitosan/polyvinyl alcohol nerve catheter, injected with brain-derived neurotrophic factor sustained-release microspheres. General observation, histological inspection, and electrophysiological determination were performed at 4 months after the surgery. This study was approved by the Research Ethics Committee of the Second Hospital of Hebei Medical University. 
RESULTS AND CONCLUSION: (1) Gross anatomy showed that muscle atrophy in group A and group D was lighter than that in the other two groups. The grafts in four groups were all adhered to the peripheral tissues, and the nerve in the autotransplantation segment was strongly adhered to the peripheral tissues. In group D, the regenerated nerve had connected the distal and proximal nerves, and the regenerated nerve filled the conduit. (2) Electrophysiological examination showed that the latency of group D was shorter than that of groups B and C (P < 0.01), and the evoked potential and conduction velocity of group D were higher than that of groups B and C (P  < 0.01). There was no significant difference between group D and group A (P > 0.05). (3) Histological observation showed that there were regenerated nerve fibers in groups B, C, and D. The diameter, number and thickness of myelin sheath of group D were larger than those of group B and group C (P < 0.01). There was no significant difference between group D and group A (P > 0.05). (4) The results showed that the injection of brain-derived neurotrophic factor microspheres into chitosan/PVA catheter had a long-term promoting effect on peripheral nerve regeneration.

Key words: materials, scaffold, nerve, nerve conduit, peripheral nerve, nerve defect, brain-derived neurotrophic factor, sustained release microspheres, nerve regeneration