Study On The Self-Assembly Material And Conductive Material Used In Repairing Nerve Defect

In this dissertation,the poly(d,1-lactic acid)/ chondroitin sulfate / chitosan (PDLLA /CS/CHS)composite materials prepared by electrostatic self-assembly(ESA) and TIPS and the polypyrrole / poly(d,l-lactic acid)(PPY / PDLLA)conductive composite material prepared by emulsion polymerization were studied used in repairing peripheral nerve defect.From the design of the biomimetic molecular and the cell compatibility surface of the extracellular matrix materials,electrostatic self-assembly technology was introduced into the surface design and modification of biomaterials.With electrostatic self-assembly technique,the chondroitin sulfate / chitosan multilayers were constructed on the surface of the PDLLA.and the bioactive multilayer surface of chondroitin sulfate / chitosan was prepared successfully.By the advantage of the natural macromolecular such as chondroitin sulfate and chitosan the shortcomings of PDLLA were overcome.Then the cell compatibility and degradation characteristics in vitro were also studied and its application was explored in the rat sciatic nerve repair.1,6-hexanediamine was adsorpted on the surface of PDLLA to introduce a polycation charge.Then chondroitin sulfate and chitosan were alternately deposited on the activated PDLLA substrate via electrostatic-self- assembly(ESA)technique.With ED AC as the cross-linker,the nerve growth factor was located on the surface of the composite material.The deposition process was monitored by UV-Vis absorbance spectroscopy.After frozen and lyophilized,the composite materials were characterized by attenuated total reflection(ATR)-FT-IR,XPS,SEM and AFM.The results showed the composite materials were modified uniformly with a dense inner layer with nanometer scale pore and a porous sponge outer layer with micron scale pore.The contact angle test results showed that with the number of self-assembly layer increased the hydrophilic increased which can improve the PDLLA hydrophobic shortcomings better.The degradation experimental and cell compatibility experiments in vitro proved that the cell compatibility of the composite materials can be improved and the degradation characteristics of the composite material can be enhanced.The components of composite material were beneficial to cell adhesion and growth.The PDLLA/CS/CHS,PDLLA/CS/CHS/NGF composite material,PDLLA and autograft were used in the repair of rat sciatic nerve defect.The rat were sacrificed after 3 months or 6 months and the implanted grafts were harvested and analyzed.The integrated analyzed results of the electrophysiological and histological observation, regeneration of nerve fibers image analysis,immunohistochemical analysis and microstructure of the materials showed that:â‘ The PDLLA/CS/CHS composite materials degraded obviously with a better degradation characteristics than those of PDLLA.After 3 months,the connective tissue wrapped materials while the materials expected incomplete and like islands.After 6 months,the materials were obvious degraded and like fragment.â‘¡The PDLLA/CS/CHS composite material had a better effect on the regeneration of the defect peripheral nerve than that of PDLLA with significant difference and it had an equal effect on the regeneration of the defect peripheral nerve with that of autograft without significant difference.After 3 months, the regenerating nerve grew well from proximal to distal with oval shape and the neural membrane was obvious.The Schwann cells were rich.After 6 months,the neural membrane of regenerating nerve was integrity and newborn neurons were bigger than those after three months with mature Schwann cells.â‘¢The PDLLA/CS/CHS /NGF composite material had the best function and had significant difference with either of PDLLA/CS/CHS or PDLLA.While there was no significant difference with autograft although it had a little better function than autograft.As a result,the ESA composite materials were superior to promote nerve growth than single materials(poly(d,1-lactic acid))and nerve growth factor-NGF can promote nerve regeneration better.A preliminary study had also made of the conductive composite materials promoting peripheral nerve repair.Taken FeCl₃ as oxidant and dopant,used SDS (sodium dodecyl sulfate)as the emulsifier for the polymerization,Polypyrrole(PPY)/ poly(d,l-lactic acid)(PDLLA)porous conductive composite material was prepared used in peripheral nerve repair.SEM,XPS and Hall Effect Testing System were used to observe the surface morphology,structural characteristics and the conductive properties of the material.The result showed that the complexes both have the advantage of non-toxic,non-stimulation,biocompatibility,a good bio-degradable and absorbability of PDLLA but also with good biocompatibility and electrical conducti-vity of polypyrrole.Animal experiments showed that conductive composite material had a better biocompatibility and degradation characteristics.In the experimental process polypyrrole had lost its web shape and was reduced than before implantation. Compared to three months,the materials degraded more obviously,neural developed matures and the connective tissue was more dense.All these indicated that the conductive composite material had some function in promoting nerve regeneration.