Reduction-responsive shell-crosslinked micelles prepared from Y-shaped amphiphilic block copolymers as a drug carrier

Biodegradable Y-shaped amphiphilic block copolymer mPEG-b-PLG-b-(PLA)2 was synthesized and characterized by 1H NMR and FTIR. The amphiphilic property of the copolymer with a mPEG-b-PLG segment as the hydrophilic arm and two PLA segments as the hydrophobic arms endows the copolymer with the ability to form core–shell nanoparticles in aqueous solution. Co-assembly of doxorubicin (Dox) and the block copolymer in selective solvent was carried out to prepare Dox-loaded micelles. The inner-shell (PLG) of the micelle was crosslinked through a carbodiimide coupling method with cystamine as the crosslinker. The crosslinked micelles exhibit reduction-responsive release of Dox and the stability in vitro was much better than non-crosslinked micelles. In acidic release condition, the total amount of Dox released could be increased due to the increased solubility of Dox. The blood clearance of Dox in different form of micelles was studied and the results show that Dox loaded in the crosslinked micelles with PEG5K as the outer shell exhibit the longest blood circulation after intravenous injection.