Role of Lipid Structure in the Mechanical Properties and Stress Profiles of Lipid Biomembranes

Lipid membranes exhibit remarkable interfacial properties determined by the chemical structure of its molecular components. Yet, they are also subject to large scale mechanical stimuli such as membrane stretching or bending. The microscopic or local stress obtained from molecular dynamics simulations provides a unique connection between atomistic details and collective mechanical properties. Based on our recent work on central decomposition of forces (Phys. Rev. Lett. 114, 258102, 2015 and J. Chem. Theory Comput. 10, 691, 2014), we calculate lateral pressure or stress profiles of coarse-grained and atomistic lipid membranes. We show that chemical features such as double bonds or ring structures in sterols have marked effects on bilayer mechanical properties as seen by large changes in the stress profiles. The effects that one type of lipid has in the stress profile of a mixed bilayer may not be universal and depend on the structure of other lipids. This is quantified in the non-additivity of the spontaneous curvature obtained from the stress profiles of PC/sterol mixtures. Finally, we show our recent efforts to include forces from long range electrostatic interactions, calculated using Ewald methods, and quantify the error in using plain cutoffs for coulombic interactions.