Study On The Composite And Its Degradation Properties Used In Repairing Nerve Defect

A kind of poly (d, 1-lactic acid) composite membrane which was prepared by solvent volatilization method was investigated to repair peripheral nerve defect. Poly (d, 1-lactic acid) was selected as the matrix, physical mix (incorporating with chitosan, β-tricalcium phosphate (β-TCP) powder and nerve growth factor (NGF)) and surface entrapment methods were adopted respectively to prepare composite membranes which have good degradation characteristics and cytocompatibility.To study the most suitable composite membrane for repairing nerve defect, the preparation process of the composite membrane and factors in influence membrane performance were studied;the pH value of degradation medium, weight loss of pure PDLLA and its composite membrane with CHS and P-TCP were observed during the degradation in vitro. In view of the degradation speed of the composite membrane matching the nerve restoring speed, we optimized the component and proportion of composite membrane and had the results: we can prepare composite membrane with good performance by solvent volatilization method and the ultrasonic dispersal technique under 20℃ and 40% humidity.The range of molecular weight of PDLLA was selected as 10×10~4~40×10~4, using ethyl acetate as solvent to confect PDLLA solution with 10% concentration, adding CHS and P-TCP powder which the grain size less than 63μm,content ratio was fixed respectively at 30% and 5%.The pH value of degradation medium, weight loss ratio of composite membrane, the variation of molecular weight of PDLLA were determinated during the degradation in vitro .We also did the XRD for degradation products and observed the variation of the morphology and microstructure of composite membrane.The results showed that: no crystallized oligomers formed during the degradation of PDLLA. A bimodal distribution which was obtained during the determination of weight average molecular weight of PDLLA and hollow membrane structure which was appeared at the degradation of PDLLA in 3 months in vivo both showed that the mechanism of hydrolytic degradation of PDLLA is heterogeneous degradation.Because the membranes are thin, the acid autocatalytic effect is not very visible. The acidity whichproduced by degradation is also not visible. Adding appropriate content of CHS and P-TCP powder can reinforce the strength of membrane, neutralize the acidity which produced by degradation products, availably adjust the pH value of the degradation medium to keep at neuter. The P-TCP and CHS powder can be promoted to dissolve or occur acid hydrolyze only at the weak acid environment in vitro.But when in animal vivo, because of the existence of enzymatic degradation and function of cells, the CHS and P-TCP powder can degradate and metabolize more quickly.So the degradation in animal vivo was obvious quicker than the degradation at the simulation body fluid in vitro.In addition, incorporating with NGF had definite influence on the variation of pH value and the weight loss ratio of composite membrane during the degradation. Hydrophilicity/hydrophobicity determinations of composite membrane showed that: adding NGF and CHS^ P-TCP powder both can improve the hydrophilicity of composite membrane.The animal experiment was to repair nerve defect by using PDLLA/NGF composite membrane. We adopted rat sciatic nerve transaction model to kept a 1 Omm nerve defect, then these defects were repaired by using nerve autografting > nerve autografting and at part placed PDLLA/NGF composite membrane.Function repair of sciatic nerve regeneration was evaluated at 6 months.The results showed that at the nerve defect part placing the composite membrane which contained NGF also can accelerate the nerve regeneration.The analysis of IR, XPS, atomic force microscopy (AFM), contact angle measurement and degradation experiment in vitro all showed that it could obtain stable hydrophilic surface on PDLLA matrix separately via chitosan and sodium alginate entrapment.The cytocompatibility was improved, and the degradation performance can be appropriately adjusted.