A study on the design rules of DLD for high throughput WBC separation

Abstract

White blood cells (WBCs) are immune cells and can be used as biomarkers by counting the number of cells and measuring intracellular proteins. Also among WBCs, peripheral blood mononuclear cells (PBMCs) can be used for immunotherapy as a cancer treatment technique. However, the number of WBCs in the blood is about 5×103 cells/μl, which is very low compared to that of the red blood cells (RBCs) is 5×106 cells/μl. Also, the maximum WBS survival time is 48 H. Thus, rapid WBC extraction in the blood is needed. The conventional equipment for extracting WBCs is large, expensive, and time-consuming. Therefore, it is challenging to extract WBCs using the current equipment with a point of care. Deterministic lateral displacement (DLD) is a size-based separation microfluidic chip in which numerous patterned posts in a fluid channel. Unlike other particle separation methods, DLD does not require additional external force or labeling and has less dilution ratio than other passive techniques. Critical diameter (Dc) is an important parameter of DLD, which is the size that determines particle motion to be separated. If the particles are smaller than Dc, they move in zigzag mode. However, if the particles are larger than Dc, they move in displacement mode, then the particles are separated. The RBCs' equivalent spherical diameter is 3-4 μm, and they are smaller than WBCs (7~30 μm). Therefore, DLD can extract WBCs from the blood when the Dc is between RBCs and WBCs. However, DLD has a high channel resistance due to its complex shape with many posts. This results in increased pressure in the DLD channel. If the sample throughput increases, the pressure also increases and affects the channel shape. The high pressure affects the shape of the DLD, which is deformed and damaged, resulting in loss of function. Therefore, the blood throughput with conventional DLD is about 0.5 ml/h, which is hard to design high blood throughput DLD. This study proposed high throughput DLD while lowering the channel pressure through 3 design rules; deep, mirrored, and parallel designs. The conventional Dc calculations do not consider the channel height parameter. However, it was confirmed through an experiment that channel height affects Dc. This study also proposes a modified equation of Dc, considering the channel height. The proposed high throughput DLD can process blood over 20 ml/h with maintaining the channel pressure below 500 KPa, securing 80% recovery, 90% purity, and viability. The high throughput DLD can process just 15 minutes to extract 5ml of WBC from the blood, while the conventional DLD takes 10 hours. It is expected that high throughput DLD can extract WBCs quickly for immunotherapy and other medical applications.