In situ gelation of PEG-PLGA-PEG triblock copolymer aqueous solutions and degradation thereof

Aqueous solutions of poly(ethylene glycol-b-[DL-lactic acid-co-glycolic acid]-b-ethylene glycol) (PEG-PLGA-PEG) triblock copolymers form a free-flowing sol at room temperature and become a gel at body temperature. In this study, in situ gel formation was investigated in rats. Upon subcutaneous injection of 33 wt % aqueous solutions of PEG-PLGA-PEG triblock copolymer into rats, transparent gels were observed. The gel showed good mechanical strength and the integrity of gels persisted longer than 1 month. The gel underwent degradation by hydrolysis and turned opaque. Degradation study showed preferential mass loss of PEG-rich segment from the in situ formed gel. Number average molecular weight determined by gel permeation chromatography decreased from 3300 to 1900 and 30% mass loss was observed over 1 month. (C) 2000 John Wiley & Sons, Inc.