Research On Synthesis And Properties Of PLGA-PU/PT Composite Microspheres

The different scale and different viscosity average molecular weight of Poly?lactic-co-glycolic acid??PLGA?was synthesized with a certain proportion of lactic acid and glycolic acid by direct polymerization.The effect of each condition on the reaction was studied by orthogonal experiment.The optimal conditions for obtaining the PLGA with the maximum viscosity average molecular weight are as follows:LA:GA is 70:30;SnCl₂/LA is0.4 wt%;the reaction temperature is 180?for 10 h.The influence of various factors on the viscosity average molecular weight of PLGA is ranked as follows:reaction time>reaction temperature>the dosage of SnCl₂,LA:GA is equal to the dosage of SnCl₂.PLGA modified polyurethane aqueous solution was synthesized by acetone method.By coacervation phase separation method,PLGA modified polyurethane microspheres?PLGA-PU microspheres?were prepared.The optimum conditions for preparing PLGA-PU microspheres are as follows:the viscosity average molecular weight of PLGA?70:30?,PLGA?80:20?and PLGA?90:10?are respectively 7300,5700 and 5000;the dosage of PLGA is 30wt%of PEG-200;R value[n?IPDI?:n?PEG?]is 4;the prepolymerization temperature is 80?for 2.5 h;the chain expansion temperature is 60?for 3 h;the solid content is 45%;and the concentration of CaCl₂ solution is 6wt%.The synthesis of PLGA-PU was confirmed by FTIR technique.The SEM diagram shows that there are some holes in the surface of microspheres,with a large number of pores and passages in it.The calcification rate was studied and the calcification rate of PLGA-PU microspheres increased rapidly at the beginning stage and then slowed to a stable level.The introduction of PLGA improved the degradation rate of polyurethane.PLGA modified polyurethane/pectin composite microspheres?PLGA-PU/PT composite microspheres?were prepared by blending 2%pectin?PT?on the basis of PLGA-PU microspheres.The infrared spectrum shows that the pectin and the PLGA modified polyurethane are bonded together by hydrogen bonds.From the SEM diagram,it shows that the surface of the small sphere is smooth and round with a small number of holes.The section shows a more solid hollow structure than PLGA modified polyurethane small spheres and the internal pores and passages are crisscrossed.The calcification rate of the composite microspheres increases rapidly and then slows down until it tends to smooth.The degradation test and compression test showed that the introduction of PT improved the degradation rate and mechanical properties of the composite microspheres.The test results of water content show that the introduction of PT improves the hydrophilic properties of the composite microspheres.Using tetracycline hydrochloride?TH?as a model drug,PLGA modified polyurethane/pectin composite microspheres?PLGA-PU/PT composite microspheres?were prepared.The results showed that the drug-loading rate of composite microspheres first increased and then decreased with the increase of feed volume,and the encapsulating rate of composite microspheres slowly decreased with the increase of dosage.The experimental results showed that the accumulating drug release rate of PLGA-PU/PT composite microspheres was higher than that of PLGA-PU microspheres,which was higher than that of pure PU microspheres;the accumulating drug release rate of PLGA-PU/PT composite microspheres under different pH was:pH=9.2>pH=7.4>pH=1.5;the accumulating drug release rate of PLGA-PU/PT composite microspheres in the alkaline environment steadily increased and reached 91.5%after 12 h,in acidic conditions it was less than 10%within 1 h,the sensitivity of pH drug loaded microspheres could protect the drug through the stomach to the intestines and other parts.The accumulating drug release rate diagram showed that PLGA and pectin modified polyurethane significantly improved the sustained release performance of polyurethane and made polyurethane more suitable for drug carrier materials.In this paper,PLGA is introduced into the main chain of polyurethane and the degradation rate of polyurethane is improved by the hydrolysis of ester bonds in PLGA.The combination of PT and PLGA modified polyurethane improved the mechanical properties of the composites based on the intermolecular hydrogen bond,while the hydrophilicity of PLGA and PU was poor,and the hydrophilic properties of the composites were improved with PT.Compared with pure polyurethane,the composite materials prepared in this paper have higher degradation rate,better mechanical properties and hydrophilic properties.This sthdy widens the application field of polyurethane materials.The study on the drug loading of the composite microspheres shows that it has pH responsiveness,can protect the drug well and continue to release the drug steadily.It provides a certain research basis for the application of modified polyurethane in the field of drug controlled release and further research.