Study On The Synthesis And Electrospinning Of Polylactide-polyethylene Glycol Copolymers

Due to its good biocompatibility and biodegradability,Polylactic acid(PLA)is regarded as a green polymer material and widely used in the biomedical field,such as biological stents,tissue engineering,surgical sutures,medical dressings,drug controlled release carrier.However,PLA has some defects,such as poor hydrophilicity and poor flexibility,which limits the application of PLA materials.In order to improve the overall performance of the materials,PLA needs to be modified.Chemical modification is one of the most common modification methods,which can improve the properties by changing the molecular structure of PLA.Polyethylene glycol(PEG)is also a kind of biological polymer,it shows low toxicity and excellent hydrophilicity.The hydrophilic segment in the PEG can be introduced into molecular chain of PLA via a copolymerization reaction.Therefore,the hydrophilicity and toughness of the PLA can be improved and its application ranges also can be widend.Nanomaterials have developed rapidly in recent years and widely used in various fields because of the excellent properties.The electrospinning is a method that canprepare nanofibers continuously and stably.The nano-materials prepared by this method show regular structure,uniform size,large specific surface area and high porosity.Silver ion is a highly effective antibacterial agent that has the inhibitory effect on most strains and does not make bacteria resistant,which is commonly used as an antibacterial ingredient in wound dressings.In this thesis,the modified PLA was used as a substrate,nanofiber membranes were prepared by electrospinning,and silver ions were loaded on the membranes to prepare antibacterial materials.The comprehensive performances of the antimicrobial membranes were investigated.The specific research content of this thesis includes the following three aspects:(1)Poly(lactic-co-polyethylene glycol)(PLA-PEG)copolymers were synthesized by ring-opening polymerization using lactide and polyethylene glycol as raw materials,stannous octoate as a catalyst.The obtained polymers were characterized by FT-IR,~1H-NMR,TG,XRD,WCA,GPC,respectively.FT-IR and ~1H-NMR tests indicated that the PLA-PEG copolymer was successfully synthesized.The results of XRD and TG tests showed that the crystallinity and thermal properties of the modified polymer are improved to some extent.Compared with unmodified PLA,crystallinity was reduced by 21%and the thermal degradation temperature was decreased by 44°C.The WCA test results demonstrated that the addition of PEG can significantly improve the hydrophilicity of PLA,the water contact angle of the copolymer was 46.70°when the ratio of PEG/LA was 9%.(2)PLA-PEG nanofiber membranes were prepared by electrospinning using trichloromethane and N,N-dimethylformamide as mixed solvents.The morphology of the samples was characterized by SEM.The effect of electrospinning parameters on the micro-morphology of the fibers was investigated to determine the optimum process parameters.The test results showed that the solution concentration,spinning voltage,solution flow rate,and receiving distance have a great influence on the electrospinning process and fiber morphology.When the solution concentration was 10%,the spinning voltage was 15 kV,the solution flow rate was 1.2 mL/h,and the receiving distance was12 cm,the spinnability of PLA-PEG was great,and the resulting fibers were uniform in shape and fine in diameter,the average diameters were ranges from500 to 600 nm.(3)Nanofiber membranes of PLA and PLA-PEG were prepared under the optimal spinning conditions.Antibacterial membranes with Ag~+loading were obtained by silver nitrate solution soaking adsorption.The morphology was characterized by SEM and the surface elements of the samples were tested by XPS.In addition,the mechanical and hydrophilic properties were tested.SEM tests showed that the fibers morphology were regular and distributed uniformly.XPS analysis demonstrated that Ag~+was successfully loaded on the nanofibers.mechanical tests revealed that the antibacterial film had excellent mechanical properties,and the elongation at break,tensile strength and maximum tensile force reached 50%,3.2 MPa,and 7.92 N respectively.Water absorption and water retention tests showed that the maximum water absorption and water retention rate of the antimicrobial film was 456%and 70%,respectively,indicating that the modified material was suitable for preparing wound dressings.The antibacterial experiments indicated that the antibacterial films had a certain antibacterial activity against Escherichia coli and Staphylococcus aureus,the maximum diameter of the antibacterial ring was about 11 mm,indicating that the Ag~+loaded PLA-PEG antibacterial films can achieve the desired antibacterial effect.