| Peripheral nerve injury is commonly encountered in modern clinical practice. It is feasible to suture the nerve without tension for small defects, however, nerve autograft is still the preferred method for comparatively large defect and is the "Golden standards" to study other treatments for peripheral nerve injury. In recent years, on the basis of the development of life science and material science as well as the progress in related physical and chemical technology, the use of tissue engineering methods to repair peripheral nerve defects has become possible, Briefly, it is the use of nerve conduits made of biological or non-biological materials to bring the ends of injury nerve together and provide the regeneration chamber for nerve regeneration. According to the fact that nerve regeneration requires nutritional factors and the guidance environment, biodegradable material polylactic acid was chosen as scaffolds and brain-derived neurotrophic factor (BDNF) as nutritional factor in this study to prepare composite conduits to promote nerve regeneration. A series of evaluations were carried out, including surface morphology, mechanical properties, hydrophilic-hydrophobic, release characteristics and the bio-activity of released BDNF, and in vivo effect on nerve regeneration in rats, to provide certain references for the clinical application of the BDNF composite conduits.The BDNF composite conduits were prepared by solvent evaporation and evaluated in vitro and in vivo. The composite conduit was immersed in phosphate buffer and the surface morphology was observed before and after immersion. Its mechanical property was tested by Universal testing machine. The hydrophilic-hydrophobic property of the conduit was studied by contact angle instrument. The results showed the tensile strength of BDNF conduit was1.80MPa, the elongation at break of it was204.17%, and the contact angle was65.4°. The results showed that the BDNF composite conduit had proper mechanical and hydrophilic-hydrophobic properties.To investigate the sustained-release profile of the conduit, a90-day’s release study was carried out in vitro. The content of BDNF in release buffer was determined by ELISA after6h,1d,4d,7d,14d,28d,60d and90d’s incubation. The results showed that BDNF was released from the conduit for at least90days, which proved the conduit had the sustained-release characteristics.In this study, the proliferative effect of BDNF on SH-SY5Y cells was used to check the activity of BDNF in the PBS buffer of composite conduits. Take cells in blank culture medium as the control group, the release buffer of6h, Id,4d,7d,14d,28d,60d,90d was co-cultured with SH-SY5Y cells for24h, then MTT was added into these culture medium. The absorbance value of every group was detected by microplate readerdetecting. Compared to control group, the release solution group had higher absorbance value with significant difference(P<0.05), which indicated that the release of BDNF from the composite conduit at different time points was bio-active.Twenty-four SD rats were randomly divided into4groups with six rats in each group:A:nerve autograft group, B:saline group, C:BDNF solution group, and D:BDNF composite conduits group. Rats in each group were fixed, anesthetized and cut to make10mm defect in left sciatic nerve. Autograft was carried out in rats in group A. For rats in group B,C and D, the epineurium was sutured with conduits. The general behavior of the rats was observed after surgery, the electrophysiological characteristics, muscle wet weight recovery rate and histological observations were studied three months later. All rats were alive after operation. After three months, the regenerative nerve of rats in BDNF composite conduits group passed the conduit and grew into the distal end. Electrophysiological detection: There were no significant differences between rats in BDNF combined conduits group and autograft group in latency period and peak amplitude (P>0.05), but the motor nerve conduction velocity was significantly lower than those in autograft group(P<0.05), though higher than those in saline and BDNF solution groups. As to triceps weight recovery rate: there were differences in atrophy for each group. The minimum degree of atrophy appeared in BDNF combined conduits group and autograft group with no significant differences between the two groups (P>0.05). Histological observation found that there were normal nerve growth in BDNF combined conduits group and autograft group. Briefly, all the results showed BDNF combined conduits could effectively promote the regeneration of peripheral nerves, which was closer to autograft and was significantly better than non-BDNF conduits. |
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