Soft pinning of liquid domains on topographical hemispherical caps

The role of lipid composition as a regulator or mediator of processes that take place in biological membranes is a very topical question, and important insights can be gained by studying in vitro model lipid mixture systems. A particular question is the coupling of local curvature to the local phases in membranes of mixed composition. Working with an experimental system of giant unilamellar vesicles of ternary composition, the curvature is imposed by approaching the membrane to a topographically (on the micron scale) patterned surface. Performing experiments, we show that domains of the more disordered phase localise preferentially to regions of higher curvature. We characterise and discuss the strength of this "caging" behaviour. In future, the setup we discuss here could prove useful as a platform to localise domains rich in membrane proteins, or to promote the onset of biochemical processes at specific locations. Finally, we note that the methods developed here could have also applications in bio-sensing, as a similar but metal coated topography can sustain plasmonic resonances.