This study aimed to prepare and optimize goserelin acetate (GOS) loaded hydrogel poly(d,l-lactic acid-co-glycolic acid) (PLGA) microsphere that is suitable for long-acting clinical treatment, investigate its structure, and regulate the initial release manner. Here, the PLGA microsphere containing Poloxamer hydrogel loaded with ∼15% (w/w) GOS was prepared by double-emulsion-solvent evaporation method and evaluated in terms of microscopic structure, physicochemical properties, and release manner in vitro and in vivo. Raman volume imaging and scanning electron microscopy studies revealed a core-shell Di-Depot structure of the microsphere, in which multi-GOS-loaded hydrogel depots were distributed in the core region. Under the interaction of hydrogel and PLGA depots, high encapsulation efficiency (94.16%) and low burst release (less than 2%) were achieved, along with the accompanying prolonged administration interval (49 days); an enhanced relative bioavailability 9.36-fold higher than that of Zoladex implant was also observed. Also, by addition of 1-5% acetic acid, the lag time was shortened to 6 days. The strategy for regulating the initial release provides new insights for manipulating the release behavior of the PLGA microspheres. The desirable property of the Poloxamer hydrogel PLGA microsphere indicated its promising application in controlled release drug delivery system.
Keywords: Di-Depot; core−shell structure; goserelin acetate; lag time; release profile regulation.