中文摘要：

分别以5种不同相对分子量（60 000、90 000和120 000）、不同乳酸/羟基乙酸比例（L/G：50/50、65/35和80/20）的聚乳酸-羟基乙酸共聚物（PLGA）为载体,采用乳化溶剂蒸发法制备载甘草次酸微球。考察了不同种类PLGA对微球载药量和包封率的影响。同时考察了不同时间点的微球体外溶蚀情况、释放介质p H值变化及体外释药速率变化。结果表明,5种PLGA对微球载药量和包封率无显著影响。PLGA相对分子量或L/G比例的增大,微球溶蚀延缓、体外释药速率减慢。采用PLGA 60000（65/35或80/20）为载体的微球,释放介质p H值下降速度明显下降,且30 d后介质p H值基本不再降低。提示载药微球的体外特征受PLGA相对分子量和L/G比例的影响显著。

英文摘要：

The glycyrrhetinic acid-loaded microspheres were prepared by solvent evaporation method with five types of poly （lactic-co-glycolic acid） （PLGA） with different molecular weights （60 000, 90 000 and 120 000） and the lactide to glycolide ratio （L/G ratio, 50/50, 65/35 and 80/20） as carriers. The effects of different types of PLGA on drug loading and encapsulation efficiency of the microspheres were investigated. The in vitro erosion performance and drug release of the obtained microspheres and pH value changes of the medium at different sampling points were also analyzed. The results showed that there was no significant differences in drug loading and encapsulation efficiency among five kinds of microspheres. The erosion rate and drug release rate were decreased with the increasing of molecular weight or L/G ratio of PLGA. In the test for microspheres with PLGA 60000 （65/35 or 80/20） as carriers, the decline rates ofpH values of the medium were significantly decreased, and the pH values were nearly not declined after 30 days. It indicated that the in vitro performance of drug-loaded PLGA microspheres was closely related to molecular weight and L/G ratio of PLGA.