A density-based threshold model for evaluating the separation of particles in heterogeneous mixtures with curvilinear microfluidic channels

Chun Kwan Chen,Bee Luan Khoo

doi:10.1038/s41598-020-75878-w

Abstract

Particle separation techniques play an important role in biomedical research. Inertial focusing based microfluidics using nonlinear channels is one of the promising label-free technologies for biological applications. The particle separation is achieved as a result of the combination of inertial lift force (FL) and Dean drag force (FD). Although the mathematical expressions of FL and FD have been well derived in prior studies, they are still complicated, which limits their popularity in practice. Recent studies modified these expressions through experiments and proposed a threshold model, which assumes that only particles larger than the threshold will be well focused. Although this threshold model has been used in recent studies, two varying versions of the threshold model (TM1 and TM2) prevents standardisation in practice. In addition, both models were developed with regular low-density particles and may not be applicable to samples with higher density or samples with irregular shapes. Here, we evaluated the threshold models with samples of different densities. Based on these evaluations, we derived a modified model (TM4), which additionally considers the factor of particle density to improve the accuracy of existing models. Our results demonstrated that TM4 could more reliably predict the sorting efficiency of samples within a wider density range.

Highlights

Particle separation techniques play an important role in biomedical research
Taking into account the differences between the two threshold models and their applicability for samples with different densities and geometries, we evaluated the accuracy of the two threshold models for various samples, including regular and non-regular polystyrene (PS) particles, non-regular polyamide (PA), polyethylene terephthalate (PET) and talcum (Talc) particles of different densities and geometries
We found that the highest recovery rates of 22.5 μm, 20.5 μm, and 26.5 μm irregular polyethylene terephthalate (iPET) particles were around 46.9 ± 2.3%, 42.1 ± 12%, 43.9 ± 4.3% and 46.2 ± 5.1% respectively (Fig. 6b–e)

Summary

Introduction

Particle separation techniques play an important role in biomedical research. Inertial focusing based microfluidics using nonlinear channels is one of the promising label-free technologies for biological applications. The use of microchannels has many advantages, including low cost, fast processing time, less sample consumption, and sample detection capabilities with high sensitivity and specificity[1,2] Because of these benefits, microfluidic technology has been widely used in biomedical applications, such as the separation of biological s amples[2]. Label-free microfluidic techniques for particle separation can be further classified as active and passive approaches Active approaches, such as acoustophoresis and dielectrophoresis, utilize external fields, while passive approaches, such as deterministic lateral displacement (DLD) and pinched flow fractionation (PFF), capitalise on hydrodynamic forces and channel geometry instead of external fields. Despite advances in these technologies, inherent problems continue to hinder their widespread application (Table S1). The radial pressure gradient generated by the centrifugal force acting on particles migrating in the curved channel will result in two counter-rotating vortices, where F D is the two counter-rotating vortices at the cross-section of the curvilinear channel generated by the higher momentum of the flowing fluid near the center, which induces a drag force acting on the p articles[11]

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