Study On Conductive Drug Loaded Hydrogel For Peripheral Nerve Regeneration

As is known to all,peripheral nerve injury is a common disease.The repair and cell regeneration of the injured part are an important link.The focus of the present study is to use Nerve conduits?NCs?to repair the damaged peripheral nerve.In order to provide more help for the repair of peripheral nerve injury,the conductive drug loaded hydrogel was prepared.The purpose is to provide high-quality environment for cell growth and provide a strong support for nerve regeneration.The conductive hydrogel was made from Sodium alginate?SA?and carboxymethyl chitosan?CMCS?through Ca²⁺crosslinking and incorporation into Polypyrrole?PPy?particles.To obtain uniform and stable conductive hydrogel,Ca²⁺was provided by glucolactone?GDL?and superfine calcium carbonate?CaCO₃?sustained release system,and PPy was prepared by static chemical oxidation of pyrrole?Py?and ammonium persulfate in low temperature.The properties of the prepared SA/CMCS/PPy hydrogels were tested and characterized.The Nerve growth factor?NGF?was loaded in the process of hydrogel preparation by physical embedding,so that the SA/CMCS/PPy/NGF conductive drug loaded hydrogel was obtained,and its release in vitro was tested,and the compatibility test both in cells and in vivo was also carried out.Under this condition,the animal experiment was carried out in groups to repair the sciatic nerve defect in rats.Finally,the evaluation was made.The structure of the conductive hydrogel was characterized by the Fu Liye transform infrared spectrometer?FTIR?and the morphology and degradation performance were characterized by scanning electron microscope?SEM?.The gelation time,equilibrium water content,swelling degree,porosity,electrochemical characteristics,conductivity,mechanical properties and thermal properties of the hydrogel were measured.The results showed that the SA/CMCS/PPy conductive hydrogel with different properties could be obtained by changing the proportion of SA to CMCS and the feed ratio of PPy at room temperature.The proportion of SA:CMCS 2:1 as the basic conditions,changing feed ratio PPy,the SA/CMCS/PPy hydrogels with gelation time of 62-88 s were gotten,that could meet the different needs of the fixed molding and injection.SEM showed that the interior of the conductive hydrogel was a porous network structure,and the regular PPy particles were evenly dispersed on the hydrogel skeleton,and the morphology and state of the hydrogel were observed after the degradation experiment.When the feed ratio of PPy was 0.20,the conductive hydrogel swelling degree was 7.511,the porosity was73.16%,the conductivity was 1.42×10^-3 S/cm and showed good electrochemical properties,that provided a favorable environment for cell growth.The mechanical properties test gave the maximum compressive stress and showed a better compression modulus.The comprehensive thermal analysis verified the smooth synthesis of the conductive hydrogel through the TGA and DSC curves,and the conductive hydrogel showed good thermal stability.NGF was used as the target drug in the synthesis process of conductive hydrogel.The enzyme linked immunosorbent assay was used to study the release performance of NGF.The results showed that when the specific gravity of SA:CMCS was 2:1,the feed ratio of PPy was 0.2 and the concentration of NGF is 50 ng/mL,the cumulative release of hydrogel was higher.The release period of NGF loaded by hydrogel was approximately 42 days.The SA/CMCS/PPy/NGF hydrogel can achieve the sustained release of NGF,and the concentration of NGF can maintain a longer period of time.With the imitation of cytoplasmic matrix reticular structure and conductive hydrogel,the conductive drug loaded hydrogrel is expected to provide a good microenvironment for repair of peripheral nerve,and promote the growth of nerve cells and nerve regeneration.In order to study the effect of SA/CMCS/PPy/NGF hydrogel on cell growth,cell experiments were carried out in vitro.The pheochromocytoma cells?PC12?,rat Schwann cells?RSC96?and bone marrow mesenchymal stem cells?BMMSC?were co cultured respectively with hydrogels,different mediums were added,electrical stimulation?ES?and the conditional control of NGF release after grouping.The results showed that after the co culturing of cells and materials,the conductive hydrogel had no cytotoxicity and was beneficial to the differentiation and adhesion of PC12 cells.The SA/CMCS/PPy/NGF hydrogel could promote the differentiation and proliferation of RSC96 cells and BMMSCs cells to a certain extent.Cells stimulated by electrical stimulation also showed more active growth and proliferation,indicating that conductive NGF loading hydrogel can promote cell culture.In order to test the in vivo compatibility of SA/CMCS/PPy/NGF hydrogel,the hydrogel was embedded in the subcutaneous tissue of rats,and was taken for first,third,fifth weeks and stained with HE to observe the histomorphology and inflammation.The results showed that the SA/CMCS/PPy/NGF hydrogel did not bring out severe inflammation in the body,no tissue lesions.In order to reflect the repair effect of SA/CMCS/PPy/NGF hydrogel on peripheral nerve injury,conductive hydrogel was used as a nerve conduit filling material to repair sciatic nerve defect in rats.The nerve conduit was obtained by PDLLA by solvent evaporation,and the 10mm defect of the sciatic nerve of rats was manufactured by operation.The tissue and morphology of the sciatic regenerative nerve and the target gastrocnemius muscle of the SD rats were investigated at month 1 and month 2 after operation.The results showed that the nerve conduit group with SA/CMCS/PPy/NGF hydrogel as filling material was close to the autologous nerve graft in the repair of nerve and the recovery of muscle tissue,and can effectively help repair damaged peripheral nerve.The conductive drug loading hydrogel provides more possibilities in the application of neural tissue engineering.