Entry effects of droplet in a micro confinement: implications for deformation-based CTC microfiltration

TL;DR

This study investigates how droplets representing circulating tumor cells deform and pass through microchannels, revealing flow regimes and optimal velocities crucial for designing effective deformation-based CTC microfiltration devices.

Contribution

It introduces a numerical analysis of droplet deformation and pressure thresholds in microchannels, identifying flow regimes and proposing an optimal velocity concept for device design.

Findings

Identified two flow regimes: squeezing and shearing.

Discovered a non-monotonic relationship between critical pressure and flow rate.

Proposed an optimal velocity for CTC filtration efficiency.

Abstract

Deformation based circulating tumor cell (CTC) microchips are a representative diagnostic device for early cancer detection. This type of device usually involves a process of CTC trapping in a confined microgeometry. Further understanding of the CTC flow regime, as well as the threshold passing-through pressure is key to the design of deformation based CTC filtration devices. In the present numerical study, we investigate the transitional deformation and pressure signature from surface tension dominated flow to viscous shear stress dominated flow using a droplet model. Regarding whether CTC fully blocks the channel inlet, we observe two flow regimes: CTC squeezing and shearing regime. By studying the relation of CTC deformation at the exact critical pressure point for increasing inlet velocity, three different types of cell deformation are observed: 1) hemispherical front, 2) parabolic front, and 3) elongated CTC co-flowing with carrier media. Focusing on the circular channel, we observe a first increasing and then decreasing critical pressure change with increasing flow rate. By pressure analysis, the concept of optimum velocity is proposed to explain the behavior of CTC filtration and design optimization of CTC filter. Similar behavior is also observed in channels with symmetrical cross sessions like square and triangular but not in rectangular channels which only results in decreasing critical pressure.