Osmotically Induced Shape Changes in Membrane Vesicles

TL;DR

This paper introduces a self-consistent free-energy model linking membrane shape and osmotic pressure, revealing nonlinear effects and stability conditions that differ from classical theories, with implications for biological and synthetic vesicles.

Contribution

It presents a novel thermodynamic framework that couples membrane mechanics and solvent entropy, altering classical stability criteria for vesicles.

Findings

Critical pressures differ significantly from Helfrich predictions.

Model agrees with simulations for various vesicle sizes.

Coupling modifies the classical stability condition for spherical vesicles.

Abstract

We develop a self-consistent free-energy framework in which membrane shape and osmotic pressure are determined simultaneously in a finite reservoir by minimizing bending elasticity and solute entropy. Solute conservation makes osmotic pressure a thermodynamic variable rather than an externally prescribed parameter, producing a nonlinear coupling between membrane mechanics and solvent entropy. This coupling modifies the classical stability condition for spherical vesicles: instability emerges from global free-energy competition rather than the linear Helfrich stability criterion. The resulting critical pressures differ by orders of magnitude from Helfrich predictions and agree with simulations for small and large unilamellar vesicles. The framework is relevant to cellular environments involving biomolecular condensate confinement as well as synthetic vesicles and the development of osmotic-pressure-driven encapsulation platforms.