New sol-gel transition hydrogels based on pluronic-mimicking copolymers grafted with oligo(lactic acids)

A novel type of polyethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers grafted with oligo(D,L-lactic acid) (OLA) on the middle PPO segment was synthesized. The Pluronic-mimicking copolymers exhibited gel-to-sol transitions with increasing temperature over a wide range of copolymer concentrations, and formed more stable hydrogel structures than Pluronic F127 copolymer in aqueous solution. The gel-to-sol phase transition temperature was controllable depending on chain length of the grafted OLA on the PPO chain. The gel-to-sol transition occurring with raising temperature was attributed to thermal destabilization and expansion of the inner hydrophobic core, which disturbed the packing order of spherical micelles required for physical gelation. The OLA grafted Pluronic mimicking hydrogels not only showed highly retarded erosion at 37°C but also sustained protein release profiles, compared to Pluronic F127 hydrogel.