Budding and Domain Shape Transformations in Mixed Lipid Films and Bilayer Membranes

TL;DR

This paper investigates the stability, shapes, and phase transitions of domains with spontaneous curvature in fluid membranes, revealing conditions for protrusions, budding, and coexistence of different domain morphologies.

Contribution

It provides a detailed phase diagram and shape analysis of membrane domains, including budding and shape transformations, based on theoretical modeling.

Findings

Protruding circular domains are stable at low impurity concentrations.

Transition from circular domains to stripe patterns occurs at higher impurity levels.

Budding occurs with increasing line tension, leading to spherical membrane buds.

Abstract

We study the stability and shapes of domains with spontaneous curvature in fluid films and membranes, embedded in a surrounding membrane with zero spontaneous curvature. These domains can result from the inclusion of an impurity in a fluid membrane, or from phase separation within the membrane. We show that for small but finite line and surface tensions and for finite spontaneous curvatures, an equilibrium phase of protruding circular domains is obtained at low impurity concentrations. At higher concentrations, we predict a transition from circular domains, or "caplets", to stripes. In both cases, we calculate the shapes of these domains within the Monge representation for the membrane shape. With increasing line tension, we show numerically that there is a budding transformation from stable protruding circular domains to spherical buds. We calculate the full phase diagram, and demonstrate a two triple points, of respectively bud-flat-caplet and flat-stripe-caplet coexistence.