Equilibrium and Non-equilibrium Behavior in Phase Separated Lipid Vesicles With Fine Temperature Control
Will Fletcher, Stanford University
In order to better understand phase behavior in lipid membranes, experiments were performed on giant unilamellar lipid vesicles consisting of a ternary lipid mixture (diPhyPC/DPPC/cholestanol). This system exhibits lateral phase separation into two coexisting liquid phases, liquid-ordered and liquid-disordered, when cooled below the phase transition temperature. This study focuses mainly on the effects of heating or cooling the membrane near the transition temperature. To do this, a novel laser-based method for controlling local temperature was developed, capable of changing temperature much faster than conventional methods. This allows for significantly deeper temperature quenches, reaching the target temperature before appreciable lipid diffusion can occur and facilitating the observation of out-of-equilibrium dynamics during phase transitions. The liquid-ordered and liquid-disordered regions were imaged using fluorescence microscopy, utilizing a fluorescent dye-labelled lipid that localizes within one phase. Membrane properties including viscosity and transition temperature were determined by flickering analysis, which examines fluctuation modes in the boundary between coexisting liquid phases. This study explores patterns at thermal equilibrium as well as morphological changes observed when temperature is rapidly perturbed – including domain nucleation during cooling, free diffusion upon rapid heating, critical behavior near the transition temperature, and the formation of periodic labyrinthine patterns.Z
Abstract Author(s): Will Fletcher, Lucia Parolini, Pietro Cicuta