title: Fluctuations of coupled fluid and solid membranes with application to red blood cells.
abstract: The fluctuation spectra and the intermembrane interaction of two membranes at a fixed average distance are investigated. Each membrane can either be a fluid or a solid membrane, and in isolation, its fluctuations are described by a bare or a wave-vector-dependent bending modulus, respectively. The membranes interact via their excluded-volume interaction; the average distance is maintained by an external, homogeneous pressure. For strong coupling, the fluctuations can be described by a single, effective membrane that combines the elastic properties. For weak coupling, the fluctuations of the individual, noninteracting membranes are recovered. The case of a composite membrane consisting of one fluid and one solid membrane can serve as a microscopic model for the plasma membrane and cytoskeleton of the red blood cell. We find that, despite the complex microstructure of bilayers and cytoskeletons in a real cell, the fluctuations with wavelengths lambda greater, similar 400 nm are well described by the fluctuations of a single, polymerized membrane (provided that there are no inhomogeneities of the microstructure). The model is applied to the fluctuation data of discocytes ("normal" red blood cells), a stomatocyte, and an echinocyte. The elastic parameters of the membrane and an effective temperature that quantifies active, metabolically driven fluctuations are extracted from the experiments.
authors.affiliation: Weizmann Institute of Science, Department of Materials and Interfaces, P.O. Box 26, Rehovot 76100, Israel.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Auth
authors.forename: S A
authors.initials: SA
authors.lastname: Safran
authors.forename: Nir S
authors.initials: NS
authors.lastname: Gov
mesh_terms: D003198:Computer Simulation; D004548:Elasticity; D004910:Erythrocyte Membrane / Q000737:chemistry* / Q000502:physiology*; D008051:Lipid Bilayers / Q000737:chemistry*; D008560:Membrane Fluidity / Q000502:physiology*; D044085:Microfluidics / Q000379:methods*; D008955:Models, Cardiovascular; D008956:Models, Chemical; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D008051:Lipid Bilayers