Morphology Transition in Lipid Vesicles: Interaction of In-Plane Order and Topological Defects

Abstract

The biological membrane can exhibit complex morphologies driven by compositional heterogeneity, however membrane curvature can also be induced by a defect-driven mechanism. We have found that in the tilted gel phase, complex shapes can form spontaneously even in a membrane containing only a single lipid component as a result of membrane defect formation. To explore this phenomenon we have carried out both experimental observations and coarse-grained computer simulations.In our study, fluorescence microscopy on giant uni-lamellar vesicles (GUVs) of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) reveals that vesicles can crumple dramatically when cooled from the untilted Lα liquid-crystalline phase into the Lβ' tilted gel phase. Similar behavior is observed in simulation studies of the system.To explain the phenomenon, we propose that the observed shape evolution is driven by the nucleation of a complex membrane micro-structure that includes topological defects in the tilt orientation. These defects induce non-uniform membrane curvature resulting in a crumpled morphology. Furthermore, we show that competition between curvature change and defect motion can trap vesicles in deeply metastable, defect-rich structures.