Non-electrical powered continuous cell concentration for enumeration of residual white blood cells in WBC-depleted blood using a viscoelastic fluid

White blood cells (WBCs) are one of the critical components whose number has to be reduced before blood transfusion, failing which adverse transfusion effects may occur in patients. However, due to the extremely low concentration of residual WBCs (r-WBCs) in WBC-depleted blood, it is difficult to quantify r-WBCs accurately without using expensive and voluminous instruments. Therefore, the development of a continuous cell concentration technique is required to produce a countable number of cells from rare cells, which cannot normally be detected. In this paper, we present a viscoelastic microfluidic device for sheathless, continuous concentration of WBCs. The device performance was evaluated using polystyrene particles with different sizes at various flow rate conditions in a non-Newtonian fluid compared to a Newtonian fluid. Large particles with a blockage ratio higher than 0.1 were tightly focused at the center and collected at the center outlet with a 98% collection ratio. Meanwhile, the viscosity effect of lysed blood samples with various hematocrits was considered. Finally, diluted WBCs with various dilution ratios were concentrated by ~18-fold and continuous concentration of WBCs in lysed blood samples was performed using a non-electrical powered hand pump sprayer. Without using an external power source, center-focused WBCs were collected at the center outlet at approximately 150 μl/min and the final number of WBCs was increased to 1.8 × 10⁴ cells/ml from undetectable levels.