Dynamic buckling of light-responsive lipid vesicles: rate-dependent mode excitation and relaxation

Vesicles made from UV-responsive lipids undergo a dynamic buckling process when photoisomerization drives a rapid area expansion. The active lipids have an azobenzene-functionalized fatty acid tail which isomerizes from trans to cis under UV light and results in an increase in surface area of up to 12%. As the area expands toward a new equilibrium, the membrane is transiently under compression and the vesicles undergo deformations. By varying the rate of UV intensity increase, we can tune the effective compression rate and thereby alter the shape response as well as the post-buckling relaxation of the membrane. Slow compression rates lead to isometric area expansion while fast rates lead to high amplitude deformations in a narrow range of excited modes. In addition, some combinations of intensities and loading rates result in an onset of irreversible processes such as budding and tubulation. We map the excited mode amplitudes and onset of irreversibility to effective loading rates and lipid composition. The results show how dynamic loading may affect morphologies in cell membranes and in membrane-based materials.