Dynamic shape transformations of fluid vesicles

Abstract

We incorporate a volume-control algorithm into a recently developed one-particle-thick mesoscopic fluid membrane model to study vesicle shape transformation under osmotic conditions. Each coarse-grained particle in the model represents a cluster of lipid molecules and the inter-particle interaction potential effectively captures the dual character of fluid membranes as elastic shells with out-of-plane bending rigidity and 2D viscous fluids with in-plane viscosity. The osmotic pressure across the membrane is accounted for by an external potential, where the instantaneous volume of the vesicles is calculated via a local triangulation algorithm. Through coarse-grained molecular dynamics simulations, we mapped out a phase diagram of the equilibrium vesicle shapes in the space of spontaneous curvature and reduced vesicle volume. The produced equilibrium vesicle shapes agree strikingly well with previous experimental data. We further found that the vesicle shape transformation pathways depend on the volume change rate of the vesicle, which manifests the role of dynamic relaxation of internal stresses in vesicle shape transformations. Besides providing an efficient numerical tool for the study of membrane deformations, our simulations shed light on eliciting desired cellular functions via experimental control of membrane configurations.