Light-Controlled Membrane Mechanics and Shape Transitions of Photoswitchable Lipid Vesicles

Giant
unilamellar vesicles (GUVs) represent a versatile model system
to emulate the fundamental properties and functions associated with
the plasma membrane of living cells. Deformability and shape transitions
of lipid vesicles are closely linked to the mechanical properties
of the bilayer membrane itself and are typically difficult to control
under physiological conditions. Here, we developed a protocol to form
cell-sized vesicles from an azobenzene-containing phosphatidyl­choline
(azo-PC), which undergoes photoisomerization
on irradiation with UV-A and visible light. Photoswitching within
the photolipid vesicles enabled rapid and precise control of the mechanical
properties of the membrane. By varying the intensity and dynamics
of the optical stimulus, controlled vesicle shape changes such as
budding transitions, invagination, pearling, or the formation of membrane
tubes were achieved. With this system, we could mimic the morphology
changes normally seen in cells, in the absence of any molecular machines
associated with the cytoskeleton. Furthermore, we devised a mechanism
to utilize photoswitchable lipid membranes for storing mechanical
energy and then releasing it on command as locally usable work.