Microscopic elasticity from MD. II. Liquid interfaces and lipid membranes

Area of Science:

• Biophysics
• Materials Science
• Computational Biology

Background:

• Lipid membranes are crucial for cellular functions, possessing complex fluid and elastic properties.
• Existing 2D elasticity theories partially describe membrane deformation, but a 3D elastic response is needed for comprehensive characterization.
• Understanding lipid structure's role in elastic energy is vital for predicting membrane behavior.

Purpose of the Study:

• To characterize the 3D elastic response of lipid membranes.
• To investigate the influence of lateral fluidity on membrane mechanics.
• To validate advanced simulation methods for elasticity profiling.

Main Methods:

• Utilized the stress-stress fluctuation (SSF) method with coarse-grained MARTINI molecular dynamics simulations.
• Applied the explicit deformation method to validate SSF results by measuring stress tensor changes.
• Analyzed local elasticity profiles, including shear moduli and compliance tensors.

Main Results:

• Demonstrated local breaking of elasticity tensor symmetries due to lateral fluidity and mechanical equilibrium.
• Observed that lipid membranes are locally fluid, with a vanishing integral of the transverse shear modulus.
• Defined key elastic moduli (area, Young's, bulk) and Poisson ratio from the compliance tensor.

Conclusions:

• The study provides critical insights into the local mechanical properties of lipid bilayers.
• Lateral fluidity significantly impacts the membrane's overall elastic response.
• The developed methods allow for accurate estimation of macroscopic properties like the bending modulus.