CO2- and thermo-responsive vesicles: from expansion-contraction transformation to vesicles-micelles transition

The amidine-and dimethylaminoethyl-containing block copolymer PADS-b-PDMAEMA was prepared by the combination of reversible addition-fragmentation chain transfer polymerization and click chemistry. Benefitting from its amphiphilic nature, the PADS-b-PDMAEMA copolymer could spontaneously form vesicles in water when the concentration was above the critical aggregation concentration. As the amidine and dimethylamino units in the copolymer are both typical CO2 responsive chemical groups, the PADS-b-PDMAEMA copolymer vesicles presented unique dual CO2 responses. Moreover, the vesicles also showed thermo-responsive behaviours due to the thermal response of the PDMAEMA block. The lower critical solution temperature (LCST) of the copolymer in aqueous solution was 42.8 degrees C. The size and morphologies of these vesicles can be adjusted by controlling the protonation/deprotonation of amidine and dimethylamino species through bubbling with CO2 or Ar. Alternating treatment with CO2 and Ar could realize a reversible expansion-contraction transformation of these vesicles. Moreover, the reversible vesicles-micelles transition could also be achieved through stimuli of temperature and gas. Due to its CO2- and thermo-responsive properties, the PADS-b-PDMAEMA vesicles were used as a carrier for drug delivery systems. Doxorubicin (DOX), an anticancer drug, was used as a model drug and loaded into the vesicles. The vesicles presented good controlled release behaviour. The release rate and level could be controlled through bubbling with CO2 and by changing the temperature.