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

Abstract

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 °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.