Correlating rheological time scales of human blood and physiology using transient flow protocols*

Blood is considered a complex fluid with a rate and time-dependent response to an applied deformation rate. At low shear rates, the bridging of fibrinogen proteins results in the formation of rouleaux structures manifesting in a large increase of overall viscosity and measurable yield stress. These internal flocculated mesostructures are however broken down under sufficient shear forces in a dynamical fashion giving rise to thermokinematic memory formation and thixotropic behavior of the blood. Thus, the rheological behavior of blood and more specifically timescales associated with thixotropic behavior in the blood can be used as a proxy to hematocrit and protein concentration in blood. We combine a series of experimental measurements with in silico flow measurements and show that using well-characterized flow protocols we can measure characteristic thixotropic timescale of blood under flowing conditions. We also present a continuum-level description of the rheological behavior based on a population balance model and correlate its model parameters to blood characteristics.