Driven fluctuations and a transition to localized mode deformations in light-responsive lipid vesicles

Giant unilamellar vesicles (GUVs) composed of photo-isomerizing lipids undergo rapid and reversible changes in stress and area upon exposure to ultraviolet (UV) and blue light. Under UV illumination, one tail of each lipid extends laterally, generating compressive stress that drives flow and area expansion. Exposure to blue light reverses this effect. In experiments, we subject GUVs to cycles of UV and blue light, controlling the rate of increase of UV intensity, ∂_tI_UV , to tune the amount of transient compression and area expansion. We find that increasing ∂_tI_UV leads to greater fluctuation amplitudes and higher peak mode numbers – as high as 7. At high enough ∂_tI_UV , we find a crossover from extended Fourier modes to the formation of a single pseudopod-like protrusion (localized mode), which can either form a bud or retract. We present a model that accounts for these high-mode-number deformations and the localized mode by considering a fluid membrane under transient compression, constrained by a fixed total area. These results demonstrate how transient compression can drive membranes to form extended deformations and novel localized modes, with potential applications ranging from photo-isomerizing lipid in therapeutic interventions to the design of artificial bio-reactors.