Review on Blood Flow Dynamics in Lab-on-a-Chip Systems: An Engineering Perspective

Under different transport mechanisms, blood flow dynamics, heavily linked to the flow shear rate conditions, in "lab-on-a-chip" (LOC) systems are found to result in varying transport phenomena. This Review examines the blood flow patterns in LOC systems through the role of viscoelastic properties such as dynamic blood viscosity and elastic behavior of the red blood cells. The study of blood transport phenomena in LOC systems through key parameters of capillary and electro-osmotic forces is provided through experimental, theoretical, and numerous numerical approaches. The disturbance triggered by electro-osmotic viscoelastic flow is particularly discussed and applied in the enhancement of the mixing and separating capabilities of LOC devices handling blood and other viscoelastic fluids for future research opportunities. Furthermore, the Review identifies the challenges in the numerical modeling of blood flow dynamics under the LOC systems, such as the call for more accurate and simplified blood flow models and the emphasis on numerical studies of viscoelastic fluid flow under the electrokinetic effect. More practical assumptions for zeta potential conditions while studying the electrokinetic phenomena are also highlighted. This Review aims to provide a comprehensive and interdisciplinary perspective on blood flow dynamics in microfluidic systems driven by capillary and electro-osmotic forces.

Anomalous crystalline ordering of particles in a viscoelastic fluid under high shear

Addition of particles to a viscoelastic suspension dramatically alters the properties of the mixture, particularly when it is sheared or otherwise processed. Shear-induced stretching of the polymers results in elastic stress that causes a substantial increase in measured viscosity with increasing shear, and an attractive interaction between particles, leading to their chaining. At even higher shear rates, the flow becomes unstable, even in the absence of particles. This instability makes it very difficult to determine the properties of a particle suspension. Here, we use a fully immersed parallel plate geometry to measure the high-shear-rate behavior of a suspension of particles in a viscoelastic fluid. We find an unexpected separation of the particles within the suspension resulting in the formation of a layer of particles in the center of the cell. Remarkably, monodisperse particles form a crystalline layer which dramatically alters the shear instability. By combining measurements of the velocity field and torque fluctuations, we show that this solid layer disrupts the flow instability and introduces a single-frequency component to the torque fluctuations that reflects a dominant velocity pattern in the flow. These results highlight the interplay between particles and a suspending viscoelastic fluid at very high shear rates.