Azobenzene-doped, lipid-bilayer vesicles with light-responsive permeability: measuring mechanical response to photochemical excitation by micropipette aspiration

Inspired by the ability of cell membranes to control the permeability of selected solutes across the lipid bilayer membrane, we report on a synthetic system that switches permeability in response to light. We use experiments and simulations to study giant unilamellar lipid vesicles that contain a photoisomerizing unit (azobenzene) that channels photochemical excitation into mechanical energy within the membrane. In experiments with micropipette aspiration, we hold the vesicles at a constant tension and expose them to UV light with controlled dosage. The membrane surface area, interior volume, and stretching modulus are all measured in situ. We find a threshold molar fraction of azobenzene, below which there is no UV-stimulated response. Above that threshold, we find an extension of the aspirated projection length within seconds of exposure. Together with a prior study of glassy membranes, our experiments and simulations show the basic principles by which the injection of photochemical energy drives the membrane away from equilibrium switching membrane properties in a reversible manner. These results will allow us to mimic cell function and to design smart, responsive artificial systems.