Synthesis and characterization of poly(amino urea urethane)-based block copolymer and its potential application as injectable pH/temperature-sensitive hydrogel for protein carrier

A series of novel block copolymer comprising of poly(ethylene glycol) (PEG) and poly(amino urea urethane) (PAUU) was simply synthesized and characterized. The block copolymers were synthesized by a polyaddition reaction between isocyanate groups of 1,6-diisocyanato hexamethylene with secondary amine and hydroxyl groups of 2-hydroxyethyl piperazine and hydroxyl groups at the ends of PEG in chloroform in the presence of dibutyltin dilaurate as a catalyst and characterized by 1H and 13C NMR, FTIR and gel permeation chromatography. Copolymer aqueous solutions exhibited pH/temperature-dependent sol–gel phase transitions with a sol-to-gel and a gel-to-sol phase transition corresponding to the increasing of pH and temperature, respectively, with low concentrations. The gel regions covered the physiological condition and could be modulated by changing PAUU fraction, molecular weight of PEG and copolymer concentration. The copolymer hydrogel did not show cytotoxicity. After injecting the copolymer solution subcutaneously into SD rats, an in situ gel formed rapidly. The copolymer hydrogel was confirmed as a protein depot carrier; it showed a sustained release of FITC-BSA over 6 weeks. This novel pH/temperature-sensitive hydrogel system is a potential applicable candidate for protein carrier.