| Background and objective:Peripheral nerve defect,with long-term treatment,usually present poor outcomes.Autologous nerve graft is used for Bridging nerve gaps.however,secondary impact of the sensory nerve to the donor site,mismatch of the nerve fiber and insufficient of nerve limited autografts.Conduit made of absorbable material present a new scope for nerve defect repair.For limitation in characters of mechanical property,biocompatibility and immune reactivity,there is no perfect conduit for clinical application.poly lactide-co-glycolide acid(PLGA)is an aliphatic polyester products,broadly apply to various kinds of tissue engineering scaffolds.However,for its brittleness and poor toughness,after shape setting,PLGA is intolerance to deformation stress and easy to break.polycaprolactone(PCL)is a semi crystalline polyester,it presents good mechanical property.in this study,we mixed the PLGA and PCL according to the proportion of 1:1,to improve its mechanical properties and biological properties,and the basic fibroblast growth factor(b FGF)combined to provide a new material for clinical repair of peripheral nerve defects.As a novel biodegradable material,we test its mechanical property,assess its biocompatibility and figure out its outcome for repairing peripheral nerve defect.Method and Result:1、Preparation of the novel material:mixed the PLGA(PLGA,LA:GA=75:25)and PCL according to the proportion of 1:1,with Phase separation method,we produced the poly lactide-co-glycolide acid/polycaprolactone(PLGA/PCL)film.The film is white.The average thickness of film is 273±6.8μm.The surface structure,pore structure and microstructure of the material were observed by electron microscopy(ESEM).The surface area of the PLGA/PCL film material is about12.72m2/g,and the pore size is 2.451 nm.2、mechanical property test: Tensile strength test using Instron 1121 electronic universal testing machine.According to the standard of GB/T1040.1-2006.The average tensile strength of PLGA/PCL film was1.23±0.02 MPa,and the average tensile elongation at break was about119.4±5.5%,and the average tensile rupture modulus was 47.7±6.5MPa.3、Protein adsorption experiments: weighed exact PLGA/PCL film material 10 mg,PBS solution immersed into bovine serum albumin,in different time points took out of the solution of BSA,280 nm UV absorption value(OD)were detected,the results showed that the materials immersed in BSA solution 24 h,protein adsorption capacity close to reach the platform.The BSA adsorption capacity of 24 h was19.26±0.88 mg/g.4、 In vitro degradation experiments were carried out by hydrolysis and enzymatic hydrolysis.The hydrolysis was carried out by using PBS buffer solution,while trypsin was used for enzymatic hydrolysis.As a result,the weight of PLGA/PCL decreased gradually with the time of hydrolysis and enzymatic hydrolysis.In the process of enzymatic hydrolysis,the degradation rate of PLGA/PCL was accelerated obviously.After 8 weeks,the weight loss was more than 60%,and the weight loss was over 90% after 14 weeks.5、 In this study,we refer to the fifth part of the national standards for evaluation of medical devices: in vitro cytotoxicity test(GB/T16886.5-2003)cytotoxicity test.The eleventh part according to the national standards of biological evaluation of medical devices: systemic toxicity test(GB/T 16886.11-1997)and Chinese Pharmacopoeia(1995version two pyrogen test pyrogen test).The PLGA/PCL film has no toxicity,no acute systemic toxicity,does not cause pyrogen reaction.6、Experimental study of PLGA/PCL film in repairing sciatic nerve defect were conducted in rats.The weights of SD rats was 110—120g,all of them were female.The experimental animals were designed as 5groups: The sham operation group(group A)5 rats,the sciatic nerve was exposed,but do not damage;simple injury group,negative control group(group B): 5 rats,cut the sciatic nerve,and cut off the length of the 10 mm nerve,no nerve repair.Autologous peripheral nerve transplantation groups(group C): 8 rats,cut sciatic nerve,the repair of nerve defect of10 mm by homologous nerve transplantation;PLGA/PCL Bridge Group(group D): 8 rats,cut sciatic nerve,the repair of nerve defect of 10 mm by PLGA/PCL conduit bridging;PLGA/PCL + b FGF bridging group(E group): 8 rats,cut sciatic nerve,the repair of nerve defect of 10 mm by b FGF immersed PLGA/PCL conduit bridging.After the animal model was made,the rats were observed and recorded every week,the death rate,body weight change,whether there were diarrhea,the appearance of the incision,whether there was swelling or infection.Whether there was toe,plantar ulcer,ulcer healing time.The results showed that all the rats survived well except two rats,and the death of the rats in the two cases had nothing to do with PLGA/PCL.All the wounds healed in rats afteroperation,no signs of infection were occurred.Different degrees of toe or plantar ulcer occurred in first week postoperatively in the groups with nerve defect.After 4 weeks,the ulcer began to heal.In groups C/D/E,rats with postoperative limb drag improved significantly in 8 to 12 weeks.There was no significant change in body weight of rats in each group.During the 16 weeks of the experiment,no rats died and no diarrhea occurred.After 12,and 16 weeks,the electrophysiological function was measured for the action potential amplitude(CAMP)and motor nerve conduction velocity(MNCV,m/s).Results at 12 th week,CAMP mean amplitude: group A was 28.45 5.492 m V,group B was 0,group C was11.36 2.295 m V group D was 9.443 2.245 m V,group E was10.03 2.957 m V。MNCV:group A 29.25 th am/s,group B was 0,group C was 15.31 3.647m/s,group D was 10.75 3.411m/s,group Ewas 12.95 4.761m/s.16 thweek,CAMP mean amplitude: group A was29.19 5.117 m V,group B was 1.615 0.846 m V,group C was15.67 3.719 m V,group D was 13.5 2.204 m V,group E was14.49 3.961 m V.MNCV: group A was 29.63 5.11m/s,group B was2.483 1.475m/s,group C was 18.79 2.695m/s,group D was14.61 2.617m/s,group E was 15.63 2.387m/s.At the end of 16 weeks,the experimental animals were sacrificed and the gastrocnemius muscles were removed.The ratio of the wet weight of gastrocnemius muscle in the experimental side to the wet weight of gastrocnemius muscle in the normal side was calculated.Results the relative wet weight percentage(84.25 2.5)% in the group A;(20 3.367)% in the B group;(46.25 3.594)%in the group C;(37 5.598)% in group D;(41.25 3.775)%in the group E.At the 16 week,the nerve tissue wasdissected and observed by HE staining.Compared with the autologousnerve graft group,the nerve sheath repair group had less adhesion,less scar tissue and less invasion of inflammatory factors.Conclusion:PLGA/PCL absorbable nerve conduit has good mechanical strength and surface porosity,its good biocompatibility,the material itself and its degradation products will not cause toxicity effects and inflammation in the body,it can effectively promote the regeneration of peripheral nerve,and prevent the obstacle around tissue and scar tissue on nerve regeneration.The compound b FGF PLGA/PCL nerve sheath tube can promote the repair of the injured nerve in the early stage,and has approximate effect as the autogenous nerve transplantation.The utility model has the value of clinical repair of peripheral nerve defects. |
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