Responsive giant vesicles filled with poly(N-isopropylacrylamide) sols or gels

We prepared giant unilamellar vesicles (GUVs) enclosing solutions or covalent gels of Poly(N-isopropylacrylamide) (PolyNipam). Concentrated suspensions of GUVs were prepared by applying an alternative field on a lipid film hydrated by a monomer solution containing N-isopropylacrylamide, crosslinker (N,N'-methylene-bis-acrylamide), initiator and sucrose. Vesicle inner medium was polymerised and crosslinked by UV irradiation of the suspension, yielding viscous vesicles enclosing a solution of linear PolyNipam chains (when no bisacrylamide was used) or elastic vesicles filled with a covalent PolyNipam gel. We show that gel-filled vesicles are responsive systems triggered by the temperature: they shrink, reducing by a factor eight their volume below the critical temperature (32 degrees C in water, lower in glucose solution) and re-swell in a reversible and reproducible way upon decreasing temperature. In both cases, we show that the vesicle lipid membrane interacts with the internal polymer, resulting in an strong resistance of the vesicles to external mechanical stresses (enhanced tension of lysis).