Ultrasound for probing the microstructure in sheared dense suspensions of red blood cells*

This study proposes to probe the anisotropic microstructure of sheared dense red blood cells (RBC) suspensions by ultrasonic scattering technique. The principle consists in measuring the structure factor, which is linked to the Fourier transform of the pair correlation function. Recent ultrasonic experiments on sheared hard-spheres suspensions [Lombard et al, J. Acoust. Soc. Am., 2020] demonstrated that the angular-dependent structure factor can detect the main angular position of regions depleted in particle pairs. We conduct here ultrasonic experiments on suspensions of disaggregated RBC sheared in a Couette flow device for several RBC volume fractions and shear rates. The measured angular-dependent structure factors are similar to those obtained for sheared hard-spheres suspensions and suggest the presence of regions depleted in cell pairs. This is corroborated by 3D numerical simulations of sheared RBC suspensions. This new ultrasonic tool will pave the way to a better understanding of the relationship between the rheology and microstructure of opaque RBC suspensions.