Abstract

Closed vesicles bounded by a single lipid bilayer membrane are known to exhibit a rich variety of shapes, especially when the bilayer is composed of more than one type of lipid. Using multiple-dye fluorescence imaging it is now possible to directly visualize these shapes in the lab. Some of the shapes observed in this way have surprising characteristics and appear to be caught in a dynamic, nonequilibrium, yet (meta)stable state. We study the vesicle shapes and use them to extract biologically relevant material parameters. Moreover, we study the dynamics of these vesicles, focussing on the most prolific shape: a vesicle containing many domains. These domains interact by deforming the membrane around them, creating a membrane mediated repulsion which results in a patterned vesicle shape. We can quantify this interaction experimentally and model it by considering the effect the domains have on the curvature of the surrounding membrane. From this model we can explain both the measured interaction strengths and observed domain size distribution. Finally, the membrane mediated interactions do not only stop the domains from coalescing and growing, but also sort them by size, resulting in regions of largely equal-sized domains. This new sorting mechanism can be understood theoretically in a model where the domains are allowed to reorganize and search for a configuration in which the total curvature of the entire membrane is minimized.