A bilinear model for the elastic response of hydrated lipid bilayers under normal pressure difference.

This article investigates the mechanical response of multilamellar phospholipid bilayer membranes to compression as a function of hydration, defined as the number of water molecules per lipid molecule, using coarse-grained molecular dynamics simulations with the MARTINI force field. The study examines four phospholipids—DOPC, DOPE, POPC, and POPE—across six hydration levels, finding that the critical increase in surface area per lipid before membrane rupture is nearly constant (~0.5 nm²) regardless of hydration or lipid type, while the critical normal pressure difference at rupture decreases inversely with hydration. A universal bilinear correlation is proposed to describe membrane stretching under normal pressure difference, normalized by critical area and pressure scales, revealing two linear regimes with slopes dependent on lipid head groups. The findings highlight hydration as a key factor influencing membrane integrity under compression, with lipid composition playing a secondary role, and provide a framework for continuum modeling of multilamellar membranes relevant to biological systems such as lung alveoli and synovial joints.