On the rheology of red blood cell suspensions with different amounts of dextran: separating the effect of aggregation and increase in viscosity of the suspending phase

TL;DR

This study examines how dextran concentration affects red blood cell aggregation and viscosity, revealing a bell-shaped relationship influenced by hydrodynamic interactions and polymer adsorption.

Contribution

It distinguishes the effects of aggregation and viscosity increase in red blood cell suspensions using combined rheological and microscopic analysis.

Findings

Maximum aggregation occurs at an optimal dextran concentration.

The bell-shaped shear thinning curve depends on suspending phase viscosity.

Hydrodynamic interactions couple aggregation and disaggregation processes.

Abstract

We investigate the shear thinning of red blood cell - dextran suspensions. Microscopic images show that at low polymer concentration, aggregation increases with increasing concentration until it reaches a maximum and then decreases again to non-aggregation. This bell shape dependency is also deduced from the rheological measurements, if the data are correctly normalized by the viscosity of the suspending phase since a significant amount of polymers adsorb to the cell surfaces. We find that the position of the maximum of this shear rate dependent bell shape increases with increasing viscosity of the suspending phase, which indicates a that the dynamic process of aggregation and disaggregation is coupled via hydrodynamic interactions. This hydrodynamic coupling can be suppressed by characterizing a suspension of 80% hematrocrit which yields good agreement with the results from the microscopical images.