Lipid vesicle formation: the transition from open disks to closed shells

The relaxation of a lecithin suspension after sonication is studied by electron microscopy. It is shown that vesicles are formed in a two‐stage process: Fragmentation into open sheets of bilayer under the action of sound and subsequent spontaneous closure of the planar disks into closed shells. A prerequisite of the discovery is a slowing down of the relaxation process by the addition of a moderate amount of cholate as an ‘edge‐actant’.