(178j) Hematocrit Separation Using Continuum-Based Diffusive Flux Model in a Trifurcated Microchannel

Platelet-enriched blood is essential for conducting diagnostics of blood-related diseases. Such enrichment is often carried out by separating RBCs, the dominant constituent, from the bloodstream. Technologies available in this context are centrifugation, fractionation, lysis, and dilution. Active techniques such as those referred to here can contaminate the sample due to the RBC cells' haemolysis. Passive devices result in lower shear stress and are preferred in this regard. Recent advancements in fabricating low-cost, micron-sized rectangular channels using polymers and elastomers have led to a new family of devices that can separate RBCs and platelets. Flow analysis is a crucial step to develop and finalise the separation technology. Molecular-level simulations, such as discrete particle dynamics (DPD), are used to study blood flow and its constituents but are computationally prohibitive for system sizes of practical interest. The continuum approach using computational fluid dynamics provides a viable alternative for investigating particle-laden blood flow in microchannels. The gains are massive when detailed analysis and repeated simulations are required for geometrically optimising biomedical devices involving blood flow.

The particulate nature of blood, specifically the role of red blood cells and their influence on flow distribution, becomes noticeable when the channel cross-section is comparable to the length scales of RBCs. Platelets are significantly smaller in size and number density and are less significant from a rheological perspective. Fahreuss observed a distinctive behaviour of RBCs in blood flow within microchannels, with a migration towards the centre of the vessel of diameter less than 300 micron. Acrivos observed a similar phenomenon in suspension experiments. These observations were mathematically explained by Philips, who delineated the fluxes of particle migration and collision frequency during species transport. More realistic blood flow studies can be conducted by integrating the Philips formulation within the continuum approach, coupled with realistic viscosity models. A detailed viscosity model developed by Apostolidis and Beris for blood is incorporated in the present work to explore its rheological and particulate aspects. The primary objective of the present study is to optimise microfluidic design parameters for achieving significant hematocrit separation. A comprehensive examination of geometrical parameters is conducted within a trifurcated channel, first described in an earlier study.

The primary objective of this study is to analyse and optimise hematocrit separation using a trifurcated microchannel. The research focuses on understanding how geometric parameters, flow conditions, and hematocrit levels influence RBC separation efficiency and the fluxes responsible for shear-induced migration. This study uses computational fluid dynamics (CFD) simulations to provide insights into the governing mechanisms and optimal design parameters for effective hematocrit separation. A single-phase treatment of blood is adopted along with shear-induced particle migration for the red blood cells. The hematocrit distribution in the channel is determined by solving a diffusive flux model (DFM) equation jointly with the mass and momentum equations. The effective viscosity of blood is determined locally by using the Beris model. Simulations clearly show an improvement in separation efficiency for narrower gaps and dilute hematocrit concentration. Efficiency is only marginally affected by the angles of the separator arms and flow rates. These results help design a viable RBC-platelet separation device for clinical diagnostics.