Unified Membrane Properties Extracted from the Thermal Fluctuations of Lipid Bilayers

Biomembranes composed of lipids and proteins are a dynamic platform that accommodate a variety of cell functions. Recent research using lipid bilayers as model biomembranes have begun to explore the hierarchy of dynamics spanning sub ps to seconds of deformations that occur in these systems. Here, we study membrane fluctuations on nanosecond time scale in mixed lipid bilayers with a same headgroup chemistry but varying alkyl tail lengths, specifically a mixture between dimyristoyl- and distearoyl-phosphatidylcholine. The equilibrium membrane dynamics, thermal bending and thickness fluctuations, were accessed using neutron spin echo (NSE) spectroscopy. The NSE results were used to calculate membrane’s viscous and elastic parameters, that is the membrane viscosity and the area compressibility and bending moduli. Combining the dynamic properties with density measurements of the mixtures and the structure determination by small-angle x-ray and neutron scattering, we successfully map out the unified dependence of each parameter on the area per molecule. The present results shed light on the synergistic structure and dynamic effects in a lipid membrane.