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Abstract

Biomimetic and biological membranes consist of lipid-protein bilayers in their fluid state. Because of their fluidity, these membranes can remodel both their molecular composition and their morphology in response to changes in their aqueous environments. Here, we will focus on morphological responses, motivated by recent experimental observations on giant vesicles. After a short reminder about curvature elasticity, two important recent developments will be described, the fine-tuning of the spontaneous curvature by membrane-bound proteins and the increased robustness of giant vesicles with spontaneously formed membrane nanotubes. The latter feature is intimately related to the concept of spontaneous membrane tension, which represents the intrinsic tension scale of curvature elasticity. Another important quantity, the mechanical membrane tension, is, in general, elusive to experimental studies of giant vesicles but can be determined in a quantitative manner by molecular simulations. One recent insight from such simulations is that it is important to distinguish tensionless bilayers from tensionless leaflets. In addition, using the stress profile obtained in the molecular simulations, we can obtain estimates for the curvature-elastic parameters. In the last part of the review, the framework of curvature elasticity is again taken up to further elucidate the morphological complexity of giant vesicles. Three aspects will be addressed: the stability of two-sphere vesicles with closed membrane necks; the curvature-induced constriction force acting on these necks, which can be used to cleave the necks and divide the vesicles in a controlled manner; and the striking polymorphism of multispheres generated by aqueous sucrose and glucose solutions.