A Pulsatile Flow-Modulation Microfluidic Sensor for Simultaneous Monitoring of Red Blood Cell Aggregation and Viscosity-Sensitive Time Constant.

Red blood cell (RBC) aggregation and viscosity-related flow resistance are important hemorheological parameters for assessing blood flow abnormalities, but their simultaneous measurement often requires multiple pumps or intermittent flow stoppage. In this study, we propose a single syringe pump microfluidic sensing method for simultaneous evaluation of RBC aggregation and transient flow response under continuous pulsatile blood delivery. The device consists of a single inlet, a main straight channel, a bifurcated test channel, and a big outlet. An optimized pulsatile-flow profile was applied by periodically switching the flow rate between high flow rate (Qh = 6 mL/h for 2 min) and low flow rate (Ql = 1 mL/h for 4 min), and the transient velocity response was analyzed to extract the time constant (λ1) as a viscosity-related indicator. After optimization, the selected flow profile provides stable and reproducible measurements of both λ1 and the RBC aggregation index (AI) while reducing unnecessary blood consumption. The λ1 shows a strong correlation with viscosity and is significantly affected by syringe air compliance. The proposed AI exhibits consistent trends when compared with conventional aggregation indices. Furthermore, it exhibits temporal stability under continuous blood flow. Finally, the method is adopted to detect time-dependent changes in blood during continuous blood infusion, which demonstrates its potential as a simple, sensitive, and practical microfluidic sensor for real-time hemorheological monitoring.