# Micro Blood Flow-Resolved Rheometry

## TL;DR

This paper introduces a new microfluidic method to accurately measure red blood cell aggregation and blood viscosity, overcoming previous limitations in microfluidic blood analysis.

## Contribution

A novel microfluidic method is introduced that addresses multiple challenges in measuring red blood cell aggregation and blood viscosity with high accuracy.

## Key findings

- The method successfully validated fluid viscosity measurements using glycerin solution.
- The method detected differences in hematocrit and dextran concentration effectively.
- Heat-shocked red blood cells showed measurable changes using the proposed technique.

## Abstract

For effectively assessing blood, red blood cell (RBC) aggregation and blood viscosity have been measured in microfluidic environments. However, the previous methods still face several challenges (dead-volume loss, RBC 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 the blood column (at least 100 μL) loaded into a driving syringe. To probe RBC 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 RBC aggregation, and syringe pump for blood viscosity). RBC aggregation index and blood viscosity are obtained from time-lapse image intensity and blood flow rate in both channels. As performance demonstrations, first, the measurement accuracy of fluid viscosity is validated with glycerin solution. Then, the present method is adopted to probe the 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.