Shape Transformations of Giant Vesicles: Extreme Sensitivity to Bilayer Asymmetry

Shape transformations of vesicles of lecithin (DMPC) in water are induced by changing the temperature which effectively changes the volume-to-area ratio. Three different routes are found which include i) symmetric-asymmetric re-entrant transitions from a dumbbell to pear-shaped state, ii) the expulsion of a smaller vesicle (budding), and iii) discocytestomatocyte transitions. All of these shape transformations are explained within a model for the bending energy of the bilayer which assumes i) that the two monolayers do not exchange lipid molecules, and ii) that the two adjacent monolayers exhibit a small difference in their thermal expansivities which is easily produced, e.g., by residual impurities.