Enhancing size-based leukocyte enrichment in a passive viscoelastic microfluidic separation device

In this work, we have analyzed the combined effect of cell concentration and viscosity on the margination of leukocytes in a bifurcated rectangular channel inertial flow. This study will help enhance the leukocyte separation efficiency of inertial microfluidic devices, as it depends on the margination of leukocytes while separating from blood. Several studies have reported the effects of various individual parameters like channel geometry, shear rate, hematocrit, sample composition, and red blood cell (RBC) geometry on the margination of leukocytes. Here, we focus on the physical phenomenon due to the variation of the bio-physical properties, like the behavior of cells and viscosity and their correlation, instead of the individual parametric study. PBS and viscoelastic fluid were used to vary the viscosity and cell concentration. Leukocyte margination was analyzed in terms of enrichment with viscosities and dilution factors. The output sample analysis was done based on the leukocyte enrichment factor. The viscosity of the PVP diluted sample was the same as that of blood by maintaining the PVP solution viscosity. All the experiments demonstrate that viscoelastic fluid improves the leukocyte margination compared to a PBS-diluted sample. However, using a higher PVP concentration decreases the margination of leukocytes. This study found that enhancing any parameter solely, like viscosity, Reynolds number, or Hydraulic diameter, is insufficient for higher margination. The combined effect of the parameters discussed here is responsible for higher margination. It can be hypothesized that the leukocyte margination mainly depends on cell-cell interaction in the focusing zone. The margination tends to be barely affected at lower and higher viscosities. Maintaining the viscosity of the blood sample, optimizing the width of the cell-free layers, and ensuring more cell-cell interaction in the focusing zone of the channel can enhance the leukocyte margination collectively.