Fundamentals of elasto-inertial particle focusing in curved microfluidic channels

Abstract

Elasto-inertial focusing in viscoelastic fluids has attracted increasing interest in recent years due to its potential applications in particle counting and sorting. However, current investigations of the elasto-inertial focusing mechanisms have mainly been focused on simple straight channels with little attention being paid to curved channels. Herein, we experimentally explore the elasto-inertial focusing behaviors of particles in spiral microfluidic channels over a wide range of flow rates, channel aspect ratios and channel radii. As compared with those observed in inertial microfluidics without viscoelasticity, the particle focusing pattern in our spiral elasto-inertial microfluidic system appears in a more interesting manner due to the complex coupling of elasticity, inertia and Dean flow effects. On the basis of the obtained data, the underlying mechanics and force competition behind the focusing behaviors are analyzed. In addition, for the first time, we propose a six-stage process model illustrating the particle focusing process in Dean-coupled elasto-inertial flows with increasing flow rate. It is interesting to find that the Dean drag force makes a significant contribution to particle focusing only at high flow rates and finally shifts the particle focusing positions into the outer channel region. Through carefully balancing the forces acting on particles, single-line 3D focusing can also be achieved at a throughput level of ∼100 μl min(-1), which is much higher than those in most existing studies. We envision that this improved understanding of the particle focusing mechanisms would provide helpful insights into the design and operation of spiral elasto-inertial microfluidic systems.

Particle manipulations in non-Newtonian microfluidics: A review

“…Moreover, the larger particles were found to move closer to the outer wall than the smaller particles due to the dissimilar size-dependences of elastic lift (inertial lift was assumed small) and Dean drag. Xiang et al later [113] performed a systematic study of elasto-inertial particle focusing in rectangular single-spiral microchannels over a wide range of flow rates, channel aspect ratios and channel radii. They found that with the increase of flow rate, particles undergo a dynamic process developing from dispersion to single-line focusing and finally multiplestreak defocusing (Fig.…”

Dean Flow Dynamics in Low-Aspect Ratio Spiral Microchannels

“…Spiral devices based on this concept have been used by us22232425 and others212627 for multitude cell sorting applications, including separation of neuroblastoma cells and C6 glioma cells22, sorting WBCs and RBCs24, separating polymorphonuclear leukocytes and mononuclear leukocytes21 and even for isolation of CTCs from blood26. In fact, Xiang et al 27. explored particle focusing dynamics in visco-elastic fluids in spiral microchannels, providing further insight into elasto-inertial focusing coupled with Dean flow.…”

Patient-Derived Airway Secretion Dissociation Technique To Isolate and Concentrate Immune Cells Using Closed-Loop Inertial Microfluidics

“…9,12,15,33 This has been explained by the balance of two forces: inertial lift force and Dean drag force, which gives optimal flow rate ( Q ) for the particle focusing in channel length of L as the function of μ and ρ are the fluid viscosity and density: $$Q\approx \frac{2\pi \mu H{W}^3}{3\rho L{a}^2{f}_{\mathrm{normalL}}}$$ where a , W , and H is the particle diameter, channel width, and height, respectively. Lift coefficient f L varies from ~0.02–0.05 for aspect ratios of microchannel from 2 to 0.5.…”

“…Xiang et al reported viscoelastic focusing in spiral microchannel, where 10- μ m particles were focused at OW side in high Re regime (>8). 33 Since elastic property of the fluid can be modified by the presence of a small amount of polymeric solutes, we suspect that different mucin content of airway secretion samples could result in dissimilar elastic force on the particle. Because of this inconsistency, it is challenging to find a separation protocol that works for all patient samples.…”