ABSTRACT
The mechanical properties of human red blood cells have been studied extensively by a variety of methods [35, 70]. The cell interior is a concentrated solution of the oxygen-binding protein hemoglobin that can be modeled as an incompressible fluid whose viscosity is elevated with respect to that of the plasma. Mature mammalian red blood cells do not contain a nucleus. The red cells are enclosed by a thin membrane consisting of a lipid bilayer and a cytoskeleton, which is a network of proteins. The cytoskeleton lies immediately inside the lipid bilayer, and its components project into the bilayer connecting the two structures together. One important property of the membrane is that it strongly resists changes in area. Considered as a thin shell, the membrane has an elastic modulus of isotropic dilation of about 500 dyn/cm, whereas the modulus of shear deformation is about 0.006 dyn/cm. The lipid molecules comprising the lipid bilayer can slide past each other relatively easily, but strongly resist being pulled apart. In this sense, the membrane behaves like a two-dimensional incompressible fluid.
