An experimental approach to blood flows : lift, diffusion and clustering

Blood is a complex fluid, a property that stems from the presence of deformable cells, mainly red blood cells, and plasma proteins. The peculiar properties of blood comes from the complex mechanical response of the cells to external flow but also to their ability to migrate transversally to flow direction, which leads to an inhomogeneous structure of the suspension, at the local scale but also within the whole capillary network.

I will present a set of experiments that combine basic microfluidic approach with more specific techniques such as digital holography or microgravity environment. I will first describe how cells are lifted up far the channel walls. This results in concentrating the cells in the center of the channels, a phenomenon that is counterbalanced by hydrodynamic interactions between them. The cumulative effect of these interactions is a non-linear and anisotropic shear-induced diffusion.
These hydrodynamic effects directly influence blood structure and rheology but also how it splits at bifurcations. I will finally discuss the contribution of the short-range adhesion forces between cells due to the presence of proteins in the plasma. It was recently found that this contribution is fundamental in the narrow channels of the capillary network.