Study Of The Optimal Preparation And Relaxation Properties Of GD-DTPA-Loaded Polylactic Acid Glycolic Acid Microspheres

Objective: To prepare Gd-DTPA-loaded PLGA microspheres for MRI contrast agents,and research its relaxed properties and release of in vitro,optimization of the preparative process.In order to lay foundation for the study of MR molecular imaging probe.Materials and methods:(1)Prepare Gd-DTPA-loaded PLGA microspheres by emulsion solvent evaporation method (water / oil / water, W / O / W). observed morphology of Gd-DTPA-loaded PLGA microspheres by optical microscope and transmission electron microscopy.the size of microspheres were measured by Laser particle size analyzer.established HPLC method for determination content of Gd-DTPA , then measured out the encapsulation efficiency of Gd-DTPA-loaded PLGA microspheres by centrifugation method. T1 relaxation times were measured by MRI scanner and then calculate out the R1 relaxation properties of Gd-DTPA-loaded PLGA microspheres.to simulate the vitro release law of Gd-DTPA-loaded PLGA microspheres in environment of PBS and double distilled water.( 2) To optimize the encapsulation efficiency of Gd-DTPA-loaded PLGA microspheres through the four factors by univariate and multivariate experiment.The four factors were the aqueous and external phase, the power and time of ultrasound,the speed of homogeneous dispersion machine.Results:(1)Microspheres were spherical were observed under the optical microscope and transmission electron microscope , the smooth surface , regular shape, uniform size, microspheres were no aggregation and adhesion.the has less electron dense material compared blank PLGA microspheres and Gd-DTPA-loaded PLGA. the average diameter of microspheres was the range, the amount of encapsulated Gd-DTPA was 15.00mg determination by HPLC, the total investment amount was 46.90mg, then calculate out the encapsulation efficiency was 31.99%.the amount of release into the environment the water environment more than in the PBS environment but the difference was not statistically significant (P = 0.09),the cumulative release curve wassimilarity between the water environment and in the PBS environment.(2)The time of ultrasonic was the greatest impact on the encapsulation efficiency of Gd-DTPA-loaded PLGA was showed in this study that were the inner and external aqueous phase, the time of ultrasound,the speed of homogeneous dispersion machine by univariate and multivariate experiment.the best preparation conditions were the sonic booms 60s, speed 10000 rpm, the aqueous phase 0.2ml (concentration 234.5mg/ml) of Gd-DTPA, the external phase with 2% PVA, 4% Nacl mixed solution.Conclusions:(1)Gd-DTPA-loaded PLGA microspheres was prepared by emulsion solvent evaporation method (water / oil / water ) and its characteristics had been studied.This method is more convenient than others, its characteristics was better (eg:the shape of microspheres).the relaxation properties of Gd-DTPA was decreased after wrapped with PLGA,what is not obvious decrease compared with other preparation methods.Gd-DTPA-loaded PLGA microspheres has similar nature of other microspheres system in vitro release study. when changed the release environment, the form of the cumulative release curve was similar,but it has important affect the amount released per unit time.(2)In this study to improve the entrapment efficiency of Gd-DTPA-loaded PLGA microspheres by univariate and multivariate experiments of the aqueous and external phase, the power and time of ultrasound,the speed of homogeneous dispersion machine. and study each factor on the encapsulation efficiency,to further enhance the preparation of microspheres laid the research foundation.