A novel pH-responsive and biodegradable triblock copolymer

poly(ethylene glycol)-poly(L-glutamic acid)-poly(L-Alanine acid) (PEG-PLGA-PLAA)

was prepared by N -carboxyl anhydride ring-opening polymerization and acidic hydrolysis.It was found that this amphiphilic copolymer can self-assemble into micelles in aqueous solution.The PLAA

PLGA and mPEG segments serve as a hydrophobic core

a pH-responsive shell and a hydrophilic corona

respectively.The morphology and properties of the micelles such as pH sensitivity

zeta potential

secondary structure and mean diameter were investigated.Doxorubicin (DOX) was encapsulated into the micelles to explore the release profiles

which exhibited in vitro pH-dependence.In acidic environment

with the formation of -helix secondary structure of poly(L-glutamic acid) segments

the PLGA segments in the triblock copolymers shrank and relocated in the micelles to trigger the release of drugs.As a result

these DOX-loaded polymeric micelles showed rapid release of DOX from the micelles in weakly acidic environments (pH=5.5) but very slow release under physiological condition (pH=7.4).