"Breathing" unimolecular micelles based on a novel star-like amphiphilic hybrid copolymer

Novel unimolecular micelles that possess a pH-induced "breathing" feature are presented in this paper. The hybrid copolymer POSS-(PAA-(PLLA-PEG)₄)₈, in which eight linear-dendritic like arms poly(acrylic acid)-(poly(l-lactide)-poly(ethylene glycol))₄ (PAA-(PLLA-PEG)₄) are grafted onto an oligomeric silsequioxane core, was synthesized via the combination of single electron transfer living radical polymerization (SET-LRP), ring-opening polymerization (ROP) and thio-bromo "click" reactions. ¹H NMR confirmed that the formed micelles were composed of a biocompatible PEG outer corona, a biodegradable hydrophobic PLA layer in the middle and inner hydrophilic PAA cavities. And, TEM results revealed that the morphology of the self-assembled micelles takes a rod-like structure. Interestingly, the formed micelles can "breathe", that is, the size of the micelles changes as pH values vary. Doxorubicin (DOX), an anticancer drug, was encapsulated into the micelles formed by POSS-(PAA-(PLLA-PEG)₄)₈ to evaluate a drug release profile. Due to its unique architecture and properties, this novel amphiphilic hybrid copolymer can be considered as a good candidate for controlled drug delivery.