Phase‐Transition‐ and Dissipation‐Driven Budding in Lipid Vesicles

Membrane budding has been extensively studied as an equilibrium process attributed to the formation of coexisting domains or changes in the vesicle area‐to‐volume ratio (reduced volume). In contrast, non‐equilibrium budding remains experimentally widely unexplored, especially when timescales fall well below the characteristic diffusion time of lipids, ${\tau }$ . We show that localized mechanical perturbations, initiated by driving giant unilamellar vesicles (GUVs) through their lipid main phase transition from the gel to the fluid phase, lead to the immediate formation of rapidly growing, localized, non‐equilibrium buds when the transition takes place at short timescales (< ${\tau }$ ). We show that these buds arise from small fluidlike perturbations and grow as spherical caps in the third dimension, since in‐plane spreading is obstructed by the continuous rigid gel‐like matrix. Accounting for membrane and bulk viscosity, we demonstrate that dissipation favors the formation of multiple buds which decrease in size with increasing bulk viscosity. Above a certain critical rate of area change, which we experimentally control by the change in temperature, the dissipative contribution to the total energy of the system exceeds the elastic contributions and multiple budding is expected. This rate depends on membrane and media viscosity and is correctly predicted, in order of magnitude, by our theoretical description.