Shape instabilities and curvature localization in photo-isomerizing lipid GUVs controlled by excitation rate and tension

We drive compression and shape instabilities in lipid membranes composed of photo-isomerizing, azobenzene-based lipids and develop quantitative design principles. Under blue or UV exposure, giant unilamellar vesicles (GUVs) undergo rapid, reversible changes in area and stress. By modulating the rate of increase of UV intensity, we tune the rate of isomerization from straight to bent lipid tails and thereby reduce tension – and even drive compression. Slow UV-ramp rates produce nearly isotropic expansion with fluctuation amplitudes up to 1,000x thermal. Ramping rates above 1/(15s) produce transient "extended modes" - lobed excitations with dominant mode numbers ranging from n = 3 to n = 7, extracted from the vesicle's equatorial contour. An increase in n with UV ramping rate is evident in multiple same-vesicle experiments as well as across vesicles. From real-space fluctuations, we measure the tension during photo-excitation and find periods of compression lasting upwards of 60s. We find quantitative agreement of the peak mode numbers and growth rates with a continuum theory of extended mode growth as a function of relative perimeter change, radius, bending modulus, initial tension, and a novel measurement of an effective dilational viscosity. In some GUVs, a single proboscis-like protrusion or "localized mode" is observed. We examine the energetics of this state theoretically. We also present results on active flows induced by patterned illumination of GUVs. In cell membranes, active proteins give rise to control of membrane tension, shape, topology, and permeability. Here, we show that we can achieve similar responses in a robust, photo-isomerizing, synthetic lipid system.