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Abstract
Single human red cells were suspended in media with viscosities ranging from 12.9
to 109 mPa s and subjected to shear flow ranging from 1/s to 290/s in a rheoscope.
This is a transparent cone-plate chamber adapted to a microscope. The motion of the
membrane around red cells oriented in a steady-state fashion in the shear field (tank-tread
motion) was videotaped. The projected length and width of the cells as well as the
frequency of tank-tread motion were measured. One-thousand eight-hundred seventy-three
cells of three blood donors were evaluated. The frequency increased with the mean
shear rate in an almost linear fashion. The slope of this dependence increased weakly
with the viscosity of the suspending medium. No correlation was found between the
frequency and four morphological red cell parameters: the projected length and width
of the cells as well as the ratio and the square root of the product of these quantities.
The energy dissipation within the red cell membrane was estimated based on the measured
parameters and compared to the energy dissipation in the undisturbed shear flow. At
constant mean shear rate the rise of the energy dissipation with viscosity is slower
whereas at constant viscosity the rise with the shear rate is steeper than in the
undisturbed shear flow. A fit of the data collected in this work to a theoretical
red cell model might allow one to determine intrinsic mechanical constants in the
low deformation regime.