A novel biodegradable ABC type triblock copolymer was synthesized by N-carboxyl anhydride ring-opening polymerization.Triblock copolymer mPEG-poly(asparthyl hydrazide)-PLAla (mPEG-PAHy-PLAla) was synthesized by hydrazine aminolysis.DOX was conjugated to the polymer through a pH-sensitive hydrazone bond.High drug-loaded polymeric micelles were obtained via the - interaction between conjugated and free DOX molecules.FTIR

dynamic light scattering

UV and TEM were used in the characterization and measurements.It was found that this polymer/drug complex could form nano-scaled core-shell-corona trilayer particles in aqueous solution.PLAla

PAHy(DOX) and PEG blocks served as the hydrophobic core

pH-sensitive shell and hydrophilic corona

respectively.The drug release experiments displayed a pH-dependent behavior that DOX release rate increased significantly as the environmental pH value dropped from physiologically 7.4 to acidic values resulted from the cleavage of hydrazone bonds and the increasing of hydrophilicity of PAHy segements at lower pH values.This new platform represents a promising candidate in the formulation of targeted drug delivery systems to the low pH tumor tissues.