Shape Fluctuations of Red Blood Cells

Abstract

The hydrodynamics of shape fluctuations of red blood cells is solved in a model that treats the geometry of the equilibrium shape exactly. The membrane is assumed to be a viscoelastic solid. The consequences for quasi-elastic light scattering are derived, including translational, rotational, and shape fluctuation effects. A light scattering experiment is described which appears to show discrete hydrodynamic modes of the sort predicted by the theory. A detailed comparison shows that the observed amplitudes of the hydrodynamic modes are not correctly given by the viscoelastic solid model. An alternative model is postulated, in which there would be two kinds of hydrodynamic shape fluctuations, corresponding to the two components of the composite membrane, the lipid and the cytoskeleton, moving in some sense independently but constraining each other.