Byeongmoon Jeonga, You Han Baeb and Sung Wan Kim,^a

^a Biomedical Polymers Research Building, Room 205, CCCD/Pharmaceutics, University of Utah, Salt Lake City, UT 84112, USA

^b Department of Materials Science and Engineering, Kwangju Institute of Science and Technology, Puk-gu, Kwangju 500-712, South Korea

Received 5 June 1999; accepted 19 August 1999. Available online 13 January 2000.

Abstract
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°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.

Author Keywords: Biodegradable hydrogel; Injectable formulation; Sol-gel transition, In situ gel; Drug release model