Fluctuations of coupled fluid and solid membranes with application to red blood cells

• Published in: Physical review. E, Statistical, nonlinear, and soft matter physics Statistical, nonlinear, and soft matter physics, 2007-11, Vol.76 (5 Pt 1), p.051910-051910, Article 051910
• Main Authors: Auth, Thorsten, Safran, S A, Gov, Nir S
• Format: Article
• Language: English
• Subjects: Computer Simulation; Elasticity; Erythrocyte Membrane - chemistry; Erythrocyte Membrane - physiology; Lipid Bilayers - chemistry; Membrane Fluidity - physiology; Microfluidics - methods; Models, Cardiovascular; Models, Chemical; Stress, Mechanical; Surface Properties
• ISSN: 1539-3755; 1550-2376
• DOI: 10.1103/PhysRevE.76.051910

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.