Micro Blood Flow-Resolved Rheometry

For effectively assessing bloods, red blood cells (RBCs) aggregation and blood viscosity have been measured in microfluidic environments. However, the previous methods still face several challenges (dead-volume loss, RBCs sedimentation, hematocrit-sensitive blood velocity, and precise flow-rate control). In this study, a novel method is suggested to resolve several issues. Air cavity (Vair = 250 μL) is secured above blood column (at least 100 μL) loaded into a driving syringe. To probe RBCs aggregation and blood viscosity, a microfluidic chip consists of a main channel (γ > 1000 s-1) and an aggregation channel (γ < 50 s-1). Blood is supplied into a microfluidic chip with two-step blood delivery (i.e., air-compression for RBCs aggregation, and syringe pump for blood viscosity). RBCs aggregation index and blood viscosity are obtained from time-lapse image intensity and blood flow-rate in both channels. As performance demonstrations, first, measurement accuracy of fluid viscosity is validated with glycerin solution. Then, the present method is adopted to probe difference in hematocrit and dextran concentration. At last, the proposed method is employed to detect heat-shocked RBCs (45 ~ 50 °C for 40 min). In conclusion, the proposed method has the ability to accurately measure substantial changes in RBCs or blood medium.