Drug release from biodegradable injectable thermosensitive hydrogel of PEG-PLGA-PEG triblock copolymers

An aqueous solution of newly developed low-molecular-weight PEG-PLGA-PEG triblock copolymers with a specific composition is a free flowing sol at room temperature but becomes a gel at body temperature. Two model drugs, ketoprofen and spironolatone, which have different hydrophobicities, were released from the PEG-PLGA-PEG triblock copolymer hydrogel formed in situ by injecting the solutions into a 37 degrees C aqueous environment. Ketoprofen (a model hydrophilic drug) was released over 2 weeks with a first-order release profile, while spironolactone (a model hydrophobic drug) was released over 2 months with an S-shaped release profile. The release profiles were simulated by models considering degradation and diffusion, and were better described by a model assuming a core-shell structure of the gel.