Swinging of Red Blood Cells under Shear Flow

Abstract

We reveal that under moderate shear stress ($\ensuremath{\eta}\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{\ensuremath{\gamma}}\ensuremath{\approx}0.1\text{ }\text{ }\mathrm{Pa}$) red blood cells present an oscillation of their inclination (swinging) superimposed to the long-observed steady tank treading (TT) motion. A model based on a fluid ellipsoid surrounded by a viscoelastic membrane initially unstrained (shape memory) predicts all observed features of the motion: an increase of both swinging amplitude and period ($1/2$ the TT period) upon decreasing $\ensuremath{\eta}\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{\ensuremath{\gamma}}$, a $\ensuremath{\eta}\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{\ensuremath{\gamma}}$-triggered transition toward a narrow $\ensuremath{\eta}\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{\ensuremath{\gamma}}$ range intermittent regime of successive swinging and tumbling, and a pure tumbling at low $\ensuremath{\eta}\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{\ensuremath{\gamma}}$ values.