Injectable and sustained delivery of human growth hormone using chemically modified pluronic copolymer hydrogels

A new injectable biodegradable hydrogel system with thermosensitive sol-gel transition behavior was developed. A series of A-B-A triblock copolymers consisting of Pluronic copolymer end-capped with D- or L-lactic acid oligomers (PL-LA_n) with various chain lengths (n = 5, 12) was synthesized. It was assumed that a pair of two triblock copolymers with enantiomeric oligolactide chains, when blended in an equimolar mixture, would form more stable, self-assembled, and stereocomplexed (ST) hydrogels. A series of blend hydrogels encapsulating human growth hormone (hGH) was prepared by varying blend ratios between PL and stereocomplexed PL copolymers. They showed sustained release of hGH via an erosion-dependent mechanism. The hydrogel with a 5% blending ratio exhibited the most delayed mass erosion as well as sustained protein release patterns in vitro possibly due to the formation of a fish-net like 3-D mesh structure. The effect of incubation condition on hGH release and degradation behaviors was also assessed.