Thermodynamic Relaxation Drives Expulsion in Giant Unilamellar Vesicles

TL;DR

This study explores how thermodynamic relaxation causes internal vesicles to be expelled from giant unilamellar vesicles during phase transitions, revealing universal relaxation dynamics with a characteristic timescale of 4-5 seconds.

Contribution

It introduces a thermodynamic model describing vesicle expulsion during phase transition, demonstrating universal relaxation behavior in GUVs.

Findings

Vesicle expulsion occurs with ~25% area decrease during phase transition.

Relaxation dynamics follow an Onsager-like thermodynamic model.

Relaxation times are consistently between 4-5 seconds.

Abstract

We investigated the thermodynamic relaxation of giant unilamellar vesicles (GUVs) which contained small vesicles within their interior. Quenching these vesicles from their fluid phase (T>Tm) through the phase transition in the gel state (T<Tm) drives the inner vesicles to be expelled from the larger mother vesicle via the accompanying decrease in vesicle area by ~25% which forces a pore to open in the mother vesicle. We demonstrate that the proceeding time evolution of the resulting efflux follows the relaxation of the membrane area and describe the entire relaxation process using an Onsager-like nonequilibrium thermodynamics ansatz. As a consequence of the volume efflux internal vesicles are expelled from the mother vesicle. Although complete sealing of the pore may occur during the expulsion, the global relaxation dynamics is conserved. Finally, comparison of these results to morphological relaxation phenomena found in earlier studies reveals a universal relaxation behaviour in GUVs. When quenched from the fluid to gel phase the typical time scale of relaxation shows little variation and ranges between 4-5 seconds.