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.