Role of shear induced diffusion in acoustophoretic focusing of dense suspensions
TL;DR: In this paper, the authors investigate the interplay between acoustic and shear induced diffusion (SID) forces in acoustophoretic focusing of dense suspensions in a microchannel and present a theoretical model which accurately predicts the width of the focused band in terms of shear rate, acoustic energy density, and particle concentration.
Abstract: We investigate the interplay between acoustic and shear induced diffusion (SID) forces in acoustophoretic focusing of dense suspensions in a microchannel. A theoretical model is presented which accurately predicts the width of the focused band in terms of shear rate, acoustic energy density, and particle concentration. The role of SID is clearly demonstrated by switching off the acoustic field, which leads to the instantaneous spreading of the focused band. At a given acoustic energy density and particle concentration, there exists a critical shear rate Γcr above which the focusing of microparticles is prevented. For Γ<Γcr, an equilibrium focused band is formed whose width remains constant downstream.
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TL;DR: In this article, the authors demonstrate the vibration-driven assembly of glass bead microparticles and iron oxide nanoparticles in contact with a photocurable hydrogel (PEGDA) over an area of 3000mm 2.
12 citations
TL;DR: In this article, it was shown that for dense suspensions like blood, in addition to typical full-relocation/zero relocation regimes, an intermediate partial relocation may occur when the buffer's impedance is not high enough.
Abstract: Bulk relocation of coflowing streams in an acoustic field occurs when there is a mismatch in acoustic impedance between the fluids. In separation of red blood cells from whole blood, for example, this relocation is prevented by ensuring that the central buffer stream has the higher impedance. This study shows that for dense suspensions like blood, in addition to typical full-relocation/zero-relocation regimes, an intermediate partial relocation may occur when the buffer's impedance is not high enough. This establishes the influence of particles in acoustic relocation, and provides a way to split any dense suspension into a concentrated central stream and a dilute side stream.
11 citations
TL;DR: The experimental result showed that the measured impedance was proportional to the number of blood cells, and the IDE array with ZnO nanowires was more sensitive than the IDE withoutnanowires.
Abstract: A disposable microfluidic chip for measuring the impedimetric ratio of blood cells was developed. The undiluted blood sample was separated into erythrocytes and leukocytes in the blood separation microchannel of the chip, and the erythrocytes and leukocytes were then driven into the measurement chambers, respectively. Inside each measurement chamber was an interdigitated electrode (IDE) array acting as a sensor for the impedimetric measurement of the blood cells. On the surface of the IDE array, ZnO nanowires were synthesized to promote the sensitivity of the impedimetric measurement. The experimental result showed that the measured impedance was proportional to the number of blood cells. The IDE array with ZnO nanowires was more sensitive than the IDE without nanowires. We also used freshly drawn venous blood samples from five healthy donors and ten informed and consenting patients for comparison. The impedimetric ratios of the five healthy donors were similar with low standard deviation, indicating that the impedimetric ratio would tend to be a reliable threshold as the indicator of erythrocytes to leukocytes. The impedimetric measurements of all patients were below the threshold. Using impedimetric measurement, the change in leukocytes could be easily monitored.
7 citations
07 Apr 2021
TL;DR: In this article, the authors show how fluid relocation in combination with primary radiation force can be used to effect medium exchange and separation of different-sized particles suspended in the fluid by controlling the flow rates and acoustic energy density.
Abstract: In an acoustofluidic system, the co-flow of fluids having a difference in acoustic impedance can result in an undesirable bulk transport (or relocation) of the fluids. In this work, we show how fluid relocation in combination with primary radiation force can be used to effect medium exchange and separation of different-sized particles suspended in the fluid by controlling the flow rates and acoustic energy density.
6 citations
TL;DR: This paper aims to review the label-free microfluidic techniques for the detection and isolation of CTCs that have the potential to preserve phenotypic and genotypic characteristics of isolated cells.
Abstract: Circulating tumor cells (CTCs) are the tumor cells that get detached from a primary tumor site and enter bloodstream circulation that promotes the metastasis condition of cancer. The detection and analysis of CTCs hold significant clinical and research value in terms of cancer diagnosis, prognosis, treatment, and drug development research. Isolation and analysis of CTCs are already proven as a promising tool for effective drug screening. CTCs in the circulation can be considered as biomarkers for the early-stage detection of cancer. CTCs also offer the opportunity to study, monitor, and ultimately gain insights into the process of cancer metastasis. Among the existing approaches, microfluidic technology has become a hot spot in CTC detection and isolation due to their promising features such as automation, high precision, accuracy and sensitivity, portability, that are amenable to the development of point-of-care devices. CTCs can be isolated from the blood by labeling the cells with tumor-specific biomarkers, but the use of chemicals for labeling may interfere with the downstream assay. This paper aims to review the label-free microfluidic techniques for the detection and isolation of CTCs that have the potential to preserve phenotypic and genotypic characteristics of isolated cells. The principle of operation, methodology, application, advantages, and limitations of the different techniques are discussed. The performance of the different techniques is assessed based on several parameters such as capture efficiency, throughput, purity, sensitivity, and cell viability. Finally, a brief discussion on the challenges, commercialization aspects, and future perspectives is presented.
5 citations
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TL;DR: In this article, it was shown that shear-induced migration of particles out of the sheared Couette gap and into the fluid reservoir, which reduces the particle concentration in the gap and thereby the observed viscosity, is consistent with a gap-limited shearinduced diffusion process normal to the plane of shear, with the relevant diffusion coefficient being proportional to the applied shear rate.
Abstract: In the course of viscometric measurements of concentrated suspensions of spheres in Newtonian fluids using a Couette device, Gadala-Maria & Acrivos (1980) observed a decrease in the suspension viscosity after long periods of shearing even though the viscosity of the pure suspending fluid remained constant under identical conditions. In the present work we demonstrate that this phenomenon is due to the shear-induced migration of particles out of the sheared Couette gap and into the fluid reservoir, which reduces the particle concentration in the gap and thereby the observed viscosity. We show further that this rate of viscosity decrease is consistent with a gap-limited shear-induced diffusion process normal to the plane of shear, with the relevant diffusion coefficient being proportional to is the applied shear rate.Additional experiments also uncovered a new phenomenon - a short-term increase in the viscosity upon initial shearing of a suspension in a Couette device - which was attributed to the diffusive migration of particles across the width of the Couette gap and thus was used to infer values of the corresponding diffusion coefficient within the plane of shear parallel to gradients in fluid velocity.In the theoretical part we demonstrate that the particle migrations that led to these observed phenomena may be explained in terms of the irreversible interparticle interactions that occur in these suspensions. From simple arguments, these interactions are shown to lead to effective diffusivities both normal to the plane of shear and normal to the direction of fluid motion within the plane of shear whose estimated magnitudes are comparable with those that were inferred from the experimental measurements. Furthermore, these interactions should induce, within a shear flow, particle drifts from regions of high to low shear stress, which are estimated to be of sufficient intensity to account for the observed initial viscosity increase mentioned above.
1,157 citations
TL;DR: In this article, a constitutive equation for computing particle concentration and velocity fields in concentrated monomodal suspensions is proposed that consists of two parts: a Newtonian constitutive equations in which the viscosity depends on the local particle volume fraction and a diffusion equation that accounts for shear-induced particle migration.
Abstract: A constitutive equation for computing particle concentration and velocity fields in concentrated monomodal suspensions is proposed that consists of two parts: a Newtonian constitutive equation in which the viscosity depends on the local particle volume fraction and a diffusion equation that accounts for shear‐induced particle migration. Particle flux expressions used to obtain the diffusion equation are derived by simple scaling arguments. Predictions are made for the particle volume fraction and velocity fields for steady Couette and Poiseuille flow, and for transient start‐up of steady shear flow in a Couette apparatus. Particle concentrations for a monomodal suspension of polymethyl methacrylate spheres in a Newtonian solvent are measured by nuclear magnetic resonance (NMR) imaging in the Couette geometry for two particle sizes and volume fractions. The predictions agree remarkably well with the measurements for both transient and steady‐state experiments as well as for different particle sizes.
886 citations
Journal Article•
726 citations
TL;DR: The theory of the acoustic radiation force is presented; a second-order, time-averaged effect responsible for the acoustophoretic motion of suspended, micrometre-sized particles in an ultrasound field.
Abstract: In this paper, Part 7 of the thematic tutorial series “Acoustofluidics – exploiting ultrasonic standing waves, forces and acoustic streaming in microfluidic systems for cell and particle manipulation ”, we present the theory of the acoustic radiation force; a second-order, time-averaged effect responsible for the acoustophoretic motion of suspended, micrometre-sized particles in an ultrasound field.
700 citations
TL;DR: In this article, a simple model for the rheological behavior of concentrated colloidal dispersions is developed for a suspension of Brownian hard spheres, where two contributions to the macroscopic stress: a hydrodynamic and a Brownian stress.
Abstract: A simple model for the rheological behavior of concentrated colloidal dispersions is developed. For a suspension of Brownian hard spheres there are two contributions to the macroscopic stress: a hydrodynamic and a Brownian stress. For small departures from equilibrium, the hydrodynamic contribution is purely dissipative and gives the high‐frequency dynamic viscosity. The Brownian contribution has both dissipative and elastic parts and is responsible for the viscoelastic behavior of colloidal dispersions. An evolution equation for the pair‐distribution function is developed and from it a simple scaling relation is derived for the viscoelastic response. The Brownian stress is shown to be proportional to the equilibrium radial‐distribution function at contact, g(2;φ), divided by the short‐time self‐diffusivity, D0s(φ), both evaluated at the volume fraction φ of interest. This scaling predicts that the Brownian stress diverges at random close packing, φm, with an exponent of −2, that is, η’0 ∼ η(1 − φ/φm)−2, ...
479 citations