Comicellization of a star block copolymer poly(ε-caprolactone)-block-poly(diethylamino)ethyl methacrylate (S(PCL-b-PDEAEMA)) and a linear block copolymer methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) (mPEG-b-PCL) was developed to enhance the stability and lower the cytotoxicity of micelles. The two copolymers self-assembled into mixed micelles with a common PCL core surrounded by a mixed PDEAEMA/mPEG shell in aqueous solution. This core-shell structure transformed to the core-shell-corona structure at high pH due to the collapse of the PDEAEMA block. The properties of the polymeric micelles were greatly dependent on the weight ratio of the two copolymers and the external pH. As increasing the mPEG-b-PCL content, the size and the zeta potential of the mixed micelles were lowered while the pH-dependent stability and the biocompatibility were improved. Moreover, an increase in pH accelerated the release of indomethacin (IND) from mixed micelles in vitro. These results augured that the mixed micelles could be applied as stable pH-sensitive release systems.
