Periodic and simultaneous quantification of blood viscosity and red blood cell aggregation using a microfluidic platform under in-vitro closed-loop circulation.

To evaluate variations of blood circulating in closed loops, hemorheological properties including blood viscosity and red blood cells (RBCs) are quantitatively measured with independent in-vitro instruments after collecting blood from a closed loop. But, most previous methods require periodic blood collections which induce several problems such as geometric differences between the fluidic channel and the in-vitro method, hemodilution, storage time, and unspecific blood flow rates. To resolve these issues, in this study, blood viscosity and RBC aggregation of blood circulating within a closed loop are measured with a microfluidic platform periodically and simultaneously. To demonstrate the proposed method, in-vitro closed-loop circulation is established by connecting several components (peristaltic pump, air compliance unit, fluid divider, and reservoir) in series. In addition, to measure blood viscosity and RBC aggregation, a microfluidic platform composed of a microfluidic device, pinch valve, and syringe pump is created. During each period, blood viscosity and RBC aggregation are measured by monitoring blood flow at constant blood flow, and image intensity at stationary blood flow. The proposed method is first employed to evaluate the effect of hematocrits and dextran concentrations on the RBC aggregation and blood viscosity by using a syringe pump (i.e., specific blood flow-rate). The method is then applied to detect the blood viscosity and RBC aggregation under in-vitro closed-loop circulation (i.e., unspecific blood flow-rate). From these experimental demonstrations, it is found that the suggested method can be effectively used to monitor the RBC aggregation and blood viscosity under in-vitro closed-loop circulation. Since this method does not require periodic collection from closed-loop circulation or an additional procedure for estimating blood flow-rate with a syringe pump, it will be effectively used to monitor variations of blood circulating in extracorporeal bypass loops.