(367i) Systematic in silico Investigation of Blood Rheology and Thixotropy

Blood as a non-Newtonian fluid shows thixotropic properties which means that its viscosity depends on the applied shear rate and the entire history of flow to which it is exposed. We implement the Dissipative Particle Dynamics (DPD) method, as a coarse-grained numerical model to investigate the origin of this thixotropy, also referred to as the thermokinematic memory, and to measure the thixotropic timescales of blood with different characteristics. In this study, a three dimensional simulation setup including red blood cells (RBCs), fluid particles (plasma) and two parallel walls for applying shear are designed. A transient shear rate starting from a high rate ramping down to low shear rates is applied to the blood by moving the walls in the opposite directions and steadily, followed by ramp up of the flow to its initial high shear rates. The average stress in the system is measured under different shear rates and plotted as a direct measure of rheological hysteresis in blood. Using different time intervals for the flow protocol, we systematically study these hysteresis areas and use this information to measure a characteristic thixotropic timescale for each hematocrit level. We also show that there are fundamental differences in measuring the hemoreological properties of blood in drag vs. pressure flows, resulting in entirely different flow curves at the steady state. By performing stress autocorrelation measurements, we also measure the residual stress of bloods with different hematocrits as an analogue to their yield stress values.