Temperature/pH-sensitive hydrogels prepared from pluronic copolymers end-capped with carboxylic acid groups via an oligolactide spacer

The Pluronic F127 triblock copolymer was end-capped by carboxyl groups using a degradable oligolactide as a spacer to confer pH- and thermo-sensitive properties. With increasing chain length of the oligolactide, the temperature-dependent sol-gel transition curve was significantly shifted to higher concentration with concomitant narrowing of the gelation temperature range. Carboxylic acid end-capped Pluronic also exhibited a peculiar pH-dependent sol-gel transition behavior. At 37°C, sharp gel-to-sol and sol-to-gel transitions were observed around pH = 4.8 and 8.2, respectively. The pH-dependent phase transition was caused by introduction of carboxylic acid groups at the ends of Pluronic F127.