2 research outputs found
The interaction of vortical flows with red cells in venous valve mimics
The motion of cells orthogonal to the direction of main flow is of importance in natural and engineered systems. The lateral movement of red blood cells (RBCs) distal to sudden expansion is considered to influence the formation and progression of thrombosis in venous valves, aortic aneurysms, and blood-circulating devices and is also a determining parameter for cell separation applications in flow-focusing microfluidic devices. Although it is known that the unique geometry of venous valves alters the blood flow patterns and cell distribution in venous valve sinuses, the interactions between fluid flow and RBCs have not been elucidated. Here, using a dilute cell suspension in an in vitro microfluidic model of a venous valve, we quantified the spatial distribution of RBCs by microscopy and image analysis, and using micro-particle image velocimetry and 3D computational fluid dynamics simulations, we analyzed the complex flow patterns. The results show that the local hematocrit in the valve pockets is spatially heterogeneous and is significantly different from the feed hematocrit. Above a threshold shear rate, the inertial separation of streamlines and lift forces contribute to an uneven distribution of RBCs in the vortices, the entrapment of RBCs in the vortices, and non-monotonic wall shear stresses in the valve pockets. Our experimental and computational characterization provides insights into the complex interactions between fluid flow, RBC distribution, and wall shear rates in venous valve mimics, which is of relevance to understanding the pathophysiology of thrombosis and improving cell separation efficiency
Examination of Flow Patterns During Droplet Formation and in Venous Valve Mimic Using ÎĽ-PIV
In this work, particle image velocimetry (PIV) was used for fluid flow visualization in both continuous and segmented-flow microfluidics. Droplet microfluidics is known for its precise and consistent volume dispersion between microliters and picoliters in volume for application ranging from molecular synthesis, drug discover, and diagnostics. But the influence of junction geometry on the process of drop formation has not been investigated. In this study, µ-PIV was used to study the internal flow during the drop formation process in flow-focus microfluidic device with and without constriction. It was found that in case of flow-focus with constriction, the shear force on the drop predominantly initiated break-off, whereas for the device without constriction pressure from the mainstream starts the drop formation but the continuous phase hinders the growth creating recirculating zones. This affected the system’s ability to produce drop of consistent volume. For continuous flow, a device was designed to mimic the venous valve of the circulatory system, where flow is known to greatly influence thrombus formation, but the biophysical mechanisms are not well understood. Solutions with varying hematocrit concentrations were used to understand its effects and the results were compared with both COMSOL simulations. At low Re of 0.6, there were vortexes present that propelled incoming particles and at higher values, flow segregation was observed created a stagnation point. These flow patterns may partly explain the distribution of red blood cells in the venous valves with implications in deep vein thrombosis