Microfluidic analysis of SCD RBC properties indicate changes in rheological properties in blood flow as the quantity of polymerized RBCs changes for both native and transfused blood. (A) The microfluidic rheology platform consists of a multilayer microfluidic device with a bifurcating blood channel designed to mimic the cross-sectional area of a small arteriole or venule as shown. The device allows for perfusion of blood at a fixed-pressure, isolated control of reduced oxygen tension to the experimental channel, as well as simultaneous measurement of RBC velocity profiles using the Kanade-Lucas-Tomasi algorithm and custom MATLAB scripts. All blood samples were prepared to a hematocrit of 25% in phosphate buffered saline. (B) RBC velocity profiles for 1 blood sample of a patient with SCD subjected to 21% oxygen and 0% oxygen showed a decrease in average velocity while demonstrating decreases in both the wall velocity (V_wall) and the max velocity (V_max). (C-F) The direct effect of polymerized sRBCs on bulk rheology is determined using an exchange transfusion technique and measuring rheological properties at 0% oxygen and comparing with the 21% oxygen condition immediately before cycling oxygen off. Exchange transfusions of SCD blood samples are prepared ex vivo at ratios of 10%, 30%, 70%, and 100% SCD blood. Rheological analysis shows an increase in the frictional resistance for each condition indicating that the presence of sickled RBCs impedes flow near the channel walls. Statistical analyses used Welch t test; ∗P ≤ .05; ∗∗P ≤ .01; ∗∗∗P ≤ .001; ∗∗∗∗P ≤ .0001. ns, not significant.