ABA-triblock copolymers from biodegradable polyester A-blocks and hydrophilic poly(ethylene oxide) B-blocks as a candidate for in situ forming hydrogel delivery systems for proteins.

Hydrogels are very attractive delivery systems for hydrophilic macromolecules such as proteins and DNA because they provide a protective environment and allow control of diffusion by adjusting cross-link densities. Physically cross-linked hydrogels generated by rapid swelling upon exposure to an aqueous environment can be obtained from ABA triblock copolymers containing hydrophobic polyester A-blocks and hydrophilic polyether B-blocks. They provide an attractive alternative to chemically cross-linked systems since they allow incorporation of macromolecular drug substances under mild process conditions. Moreover, they show controlled degradation behavior and excellent biocompatibility. In this review the synthesis and characterization of ABA triblock copolymers from polyester hard segments and poly(ethylene oxide) [PEO] soft segments as well as their biological and degradation properties will be discussed. Their use as biodegradable drug delivery devices in the form of implants, micro- and nanospheres has attracted considerable interest especially for proteins and may provide an alternative to poly(lactide-co-glycolide).