Responsive microgels-based colloidosomes constructed from all-aqueous pH-switchable coacervate droplets

Colloidosomes made of stimuli-responsive microgels offer the opportunity to design polymeric capsules with a hierarchical and tunable pore distribution. Coacervates stabilized by a microgel monolayer represent a unique strategy to build colloidosomes from all-aqueous emulsion drops, while exploiting the sequestration and dissolution properties of the coacervates.

Methacrylated poly(N-isopropylacrylamide) (pNIPAM) microgels are used to stabilize coacervates made of an ampholyte polymer at a pH close to its isoelectric point. They are further cross-linked under UV-irradiation. The resulting assemblies are studied by means of confocal microscopy. Their permeability towards dextrans and nanoparticles is studied before and after dissolution of the coacervate.

PNIPAM microgels are found to stabilize the coacervates by adsorbing at their surface. Inter cross-linking the microgels results in the formation of an elastic colloidosome that persists after the coacervate dissolution and withstands surface deformations up to about 200%. The coacervate is exploited as a sequestrating core to entrap a water-soluble payload, which can be further released upon coacervate dissolution, while the membrane exhibits a size-selecting permeability. The membrane properties can also be switched by the volume phase transition of the microgels. Coacervate-embedded colloidosomes open new perspectives in the area of encapsulation/extraction and controlled transport of water-soluble/dispersed species.