Abstract: Aim Polylactic acid (PLA) or polylactide co glycolide (PLGA) was used as biodegradable and biocompatible carriers to achieve sustained release of estradial PLGA/PLA Microspheres (E2 PLGA/PLA MS). THF was added in the organic phase to study its effects on the properties of MS. Methods MS were formed by an emulsification solvent extraction method with mixture of ethyl acetate (EtoAc) and tetrahydrofuran (THF) as the organic solvents, and then the properties and in vitro drug release behavior were examined. Results The results indicated that the drug loading efficiency decreased when THF added, but when the ratio of EtoAc was more than 50%, there was no obvious effect of THF ratio, but the particle size increased accordingly. The carriers' properties and the drug contents were the main factors influencing the in vitro drug release. Conclusions By controlling the technology and formulation, we can get sustained release E2 biodegradable microsperes with proper particle size, drug content and low burst release, although THF with readily solubility in water was used in the organic phase.

Key words: PLA/PLGA, PLA/PLGA, estradiol, estradiol, microspheres, microspheres, THF, THF, emulsification solvent extraction method, emulsification solvent extraction method