Compound droplet dynamics of a tumor cell squeezing through conical microfilters

Circulating tumor cells (CTCs) are regarded as important biomarkers for early cancer detection and treatment. Decades of research have made progress in CTC detection using deformability-based microfilters; however, developing a high-throughput CTC microfilter remains a challenging task due to the lack of the essential understanding of microscopic multiphase flow. To design and optimize a CTC microfilter, in-depth studies of the dynamics of a CTC squeezing through a confined constriction are necessary. In this study, numerical simulation was employed. Utilizing the octree-based Adaptive-Mesh-Refinement algorithm, a CTC was modeled as a compound Newtonian droplet moving through a microfilter with non-uniform cross sections. The immiscible interface was tracked by the volume-of-fluid method with the surface tension accounted for using the continuum surface force method. Pressure signature, shear stress and instantaneous cell velocity during the passing process through a conical microfilter were investigated in great detail in order to understand the fluid dynamics affecting the cell squeezing process. Then, the crucial design parameters including pore angles and operating flow rates were analyzed. The shear stress and critical pressure under different flow rates were investigated as well. Results reveal that the deformation-induced surface tension pressure of the cell nucleus is the dominant component of the critical pressure. Additionally, the maximum instantaneous cell velocity, shear stress and pressure all occur at the same critical stage, as the nucleus passes through the exit of the microfilter channel. Our study provides insights into the dynamics of a compound droplet squeezing through a conical-shaped microfilter and offers constructive guidance for the design and optimization of high-throughput CTC microfilters.