Non-monotonic blood viscosity and cell free layer dependence on cell aggregation

In blood flow, large proteins in the blood plasma induces attraction between red blood cells (RBCs) and form columnar aggregates. As inter-cell attraction increases due to increased protein concentration as result of physiological changes, aggregate size and shape change. Such structural changes could strongly affect blood flow in micro-vessels where aggregate size is comparable to vessel diameter. We employ hybrid lattice Boltzmann -- Langevin dynamics to investigate how increasing inter-cell attraction affect the aggregate structure, flow-induced cell free layer, and blood viscosity in micro-vessels. We find that the cell free layer thickness exhibits non-monotonic dependence on aggregation, leading to shear-thinning and shear-thickening dependence on inter-cell attraction. We identify the structure-dynamics coupling mechanisms responsible for the complex dependence.