Deduction of intrinsic mechanical properties of the erythrocyte membrane from observations of tank-treading in the rheoscope

Measurements of the dimensions and membrane rotational frequency of individual erythrocytes steadily tank-treading in a Rheoscope are used to deduce the surface shear viscosity (η_m) and the shear elastic modulus (μ_m) of the membrane. Previously published algorithms (Trans-Son-Tay et al., Biophys. J. 46: 65, 1984, and 51: 915, 1987) plus an assumed area-conserving membrane velocity field (Secomb and Skalak, Q.J. Mech. Appl. Math. XXXV 2: 233, 1982) are applied to calculate η_m as a function of the second invariant of the surface strain rate and μ_m as a function of the second invariant of membrane strain. The results indicate density-related increases in membrane stiffness and viscosity, shear-thinning viscous behavior, and strain-stiffening elastic behavior.