Extensional recovery of an intact erythrocyte from a tank-treading motion.

Normal human erythrocytes suspended in shear flow are stretched into quasi ellipsoidal forms while their membranes rotate smoothly (tank-treading). Following abrupt cessation of shear the cells recover their discoidal shapes approximately exponentially, in the manner of a Kelvin-Voigt (K-V) solid. To test the hypothesis that the recovery process is membrane-controlled, the effects of initial deformation, cytoplasmic viscosity and membrane surface-to-volume ratio were studied. It was concluded that the membrane dynamics dominates the transient shape recovery, and that the characteristic recovery time is dependent on the initial deformation. Hence, the usual simplified analysis based on retraction of a plane sheet of K-V material with constant moduli appears to be an inadequate treatment of transient whole cell recovery.