Active surface flows modify stability of phase-separated lipid membrane domains*

Phase separation of multicomponent lipid membranes is characterized by circular domains, which nucleate and coarsen slowly in time as ∼ t^1/3, following classical theories of coalescence and Ostwald ripening. In this work, we study both the coarsening kinetics and morphology of phase-separating lipid membranes subjected to nonequilibrium forces and flows transmitted by motor-driven gliding actin filaments. We experimentally observe that surface flows, driven by an adsorbed contractile actomyosin cortex, trigger rapid coarsening of non-circular membrane domains that grow as ∼ t^2/3, a 2× acceleration in the growth exponent compared to passive coalescence and Ostwald ripening. We describe these results using analytical theories based on the Smoluchowski coagulation model and the phase field model to predict the domain growth in the presence of active flows. Moreover, we demonstrate that in an alternative flow field, in which actin is instead driven along a substrate by adsorbed myosin, active flows destabilize lipid domain interfaces. As these interfaces become unstable, the domains break up, refining the overall structure, as evidenced by a shift in the structure factor toward higher wavenumbers. Our work demonstrates that active matter forces may be used to control the growth and morphology of membrane domains driven out of equilibrium.