Microscopic Stress in Biomembranes: A Perspective on Key Concepts, Methods, and Applications.

Abstract

Cell membranes are complex assemblies of lipids, proteins, and sterols whose organization and stability arise from a delicate balance of intra- and intermolecular forces, entropic effects, and external stresses. The distribution of forces within these membranes underpins their diverse functions and structural stability. The microscopic stress tensor provides a tool to connect this molecular-level force distribution to a mechanical description of the membrane. It offers a powerful framework for assessing leaflet asymmetry and for guiding molecular dynamics (MD) simulations toward accurate modeling of compositionally asymmetric bilayers. Moreover, the stress tensor bridges particle-based models with continuum mechanics, providing a feasible route for estimating key elastic moduli. Despite its promise, calculating microscopic stress in particle-based systems remains challenging due to the lack of a rigorous definition at the molecular scale. Long-range potentials and many-body interactions further complicate the stress formulation, and as a result, local stress calculations remain relatively underexplored. Existing computational approaches are largely limited to system-averaged stresses, leaving fundamental questions of force distribution and anisotropy unresolved. In this perspective, we summarize the historical development and current status of microscopic stress formulations for particle-based models, clarify major conceptual controversies, and identify methodological limitations of existing tools. Additionally, we present new data illustrating best practices for accurate stress calculation in biomembranes and discuss how force-field coarse-graining influences these outcomes. Finally, we outline emerging applications of microscopic stress analysis in studying lipid chemistry, leaflet asymmetry, small-molecule permeation, and transmembrane protein function.