Asymmetric Microchannel Research Articles

Preparation of monodisperse water-in-oil emulsions using microchannel homogenization

The droplet size and uniformity of water-in-oil (W/O) emulsions are important properties governing their stability in diverse applications. Monodisperse emulsions are preferred over polydisperse emulsions because their droplet size and distribution are easier to control. Here, we prepared (relatively) monodisperse W/O emulsions using microchannel homogenization (MCH) with an asymmetric straight-through microchannel (MC) array chip. Numerous asymmetric straight-through MCs, each comprising a microslot and circular microhole (diameter: 10 µm), were microfabricated on a silicon-on-insulator chip. We investigated the effects of emulsifier concentration, continuous-phase viscosity, dispersed-phase volume fraction, and the operating pressure of coarse W/O emulsions on the preparation of W/O emulsions, droplet size, and size distribution. The continuous phase was composed of soybean or medium-chain triglyceride oil solutions with tetraglycerin monolaurate condensed ricinoleic acid ester as the emulsifier. The dispersed phase was a Milli-Q water solution containing NaCl and/or polyethylene glycol (m.w. 20,000). The results demonstrate the suitability of MCH for the preparation of monodisperse W/O emulsions with an average droplet diameter of 12–15 µm and 8% lowest coefficient of variation using hydrophobically surface-treated asymmetric straight-through MCs with appropriately selected emulsion compositions and operating conditions.

Impact of Neurons on Patient-Derived Cardiomyocytes Using Organ-On-A-Chip and iPSC Biotechnologies

In the heart, cardiac function is regulated by the autonomic nervous system (ANS) that extends through the myocardium and establishes junctions at the sinus node and ventricular levels. Thus, an increase or decrease in neuronal activity acutely affects myocardial function and chronically affects its structure through remodeling processes. The neuro-cardiac junction (NCJ), which is the major structure of this system, is poorly understood and only a few cell models allow us to study it. Here, we present an innovant neuro-cardiac organ-on-chip model to study this structure to better understand the mechanisms involved in the establishment of NCJ. To create such a system, we used microfluidic devices composed of two separate cell culture compartments interconnected by asymmetric microchannels. Rat PC12 cells were differentiated to recapitulate the characteristics of sympathetic neurons, and cultivated with cardiomyocytes derived from human induced pluripotent stem cells (hiPSC). We confirmed the presence of a specialized structure between the two cell types that allows neuromodulation and observed that the neuronal stimulation impacts the excitation-contraction coupling properties including the intracellular calcium handling. Finally, we also co-cultivated human neurons (hiPSC-NRs) with human cardiomyocytes (hiPSC-CMs), both obtained from the same hiPSC line. Hence, we have developed a neuro-cardiac compartmentalized in vitro model system that allows us to recapitulate the structural and functional properties of the neuro-cardiac junction and that can also be used to better understand the interaction between the heart and brain in humans, as well as to evaluate the impact of drugs on a reconstructed human neuro-cardiac system.

Controllable Size-Independent Three-Dimensional Inertial Focusing in High-Aspect-Ratio Asymmetric Serpentine Microchannels.

High-throughput three-dimensional (3D) focusing of cells is the key prerequisite for enabling accurate microfluidic cell detection and analysis. In this work, we develop a high-aspect-ratio asymmetric serpentine (HARAS) microchannel for single-line inertial focusing of particles and cells at the 3D center of the channel. The mechanism of 3D focusing is explored by numerical simulation, and the focusing performances of differently sized particles are characterized experimentally at different flow rates. The results demonstrate the outstanding 3D single-line focusing capability of our HARAS microchannel. In addition, the phenomena of size-independent and position-controllable focusing over wide flow rates are observed. Finally, the applicability of our HARAS microchannel for processing real biological cells is validated by the 3D single-line focusing of A549 cells and MCF-7 cells. Our work overcomes the issue of off-centered focusing of most previous works and provides new insights into the 3D focusing in inertial microfluidics. The proposed HARAS microchannel is extremely easy for mass production and may provide a stable, high-throughput, and position-controllable scheme for subsequent single-cell detection and analysis.

Heat transfer analysis in the peristaltic flow of Casson nanofluid through asymmetric channel with velocity and thermal slips: Applications in a complex system

This investigation articulately addresses the role of gold nanoparticles in medical sciences from a different perspective. Aiming to highlight the significant usage of nanoparticles, four different types such as spherical, platelets, cylindrical and brick-like nanoparticles are brought into consideration with the main focus to achieve maximum heat enhancement. This motivation leads to mathematically formulating an electroosmosis blood flow. Casson fluid is treated as physiological fluid through an asymmetric microchannel. The nonlinear term of radiative heat flux is added on the right-hand side of the heat equation to report the impact of radiation which is beneficial in skin diseases. A closed-form solution is achieved with the help of physical approximation. Moreover, analytical expressions for velocity distribution, temperature field, shear stress, heat transfer rate and pressure gradient have been provided. The expression of stream function is also presented and the trapping phenomena are discussed. Besides studying the tremendous capacity of gold particles to enhance the heat transfer rate for targeting the maligned tissues as a prime objective, the current survey will also assist readers to explore the other similar metallic particles which can effectively be used as an alternative.

A Perturbed Asymmetrical Y-TypeSheathless Chip for Particle Control Based on Adjustable Tilted-Angle Traveling Surface Acoustic Waves (ataTSAWs).

The precise control of target particles (20 µm) at different inclination angles θi is achieved by combining a perturbed asymmetric sheathless Y-type microchannel and a digital transducer (IDT). The offset single-row micropillar array with the buffer area can not only concentrate large and small particles in a fixed region of the flow channel, but also avoid the large deflection of some small particles at the end of the array. The addition of the buffer area can effectively improve the separation purity of the chip. By exploring the manufacturing process of the microchannel substrate, an adjustable tilted-angle scheme is proposed. The use of ataTSAW makes the acoustic field area in the microchannel have no corner effect region. Through experiments, when the signal source frequency was 33.6 MHz, and the flow rate was 20 µL/min, our designed chip could capture 20 µm particles when θi = 5°. The deflection of 20 µm particles can be realized when θi = 15°–45°. The precise dynamic separation of 20 µm particles can be achieved when θi = 25°–45°, and the separation purity and efficiency were 97% and 100%, respectively.

Combining liquid inertia and evaporation momentum forces to achieve flow boiling inversion and performance enhancement in asymmetric Dual V-groove microchannels

Increasing critical heat flux (CHF) and heat transfer coefficient (HTC), and reducing pressure drop (Δp) are highly desirable during flow boiling. An asymmetric Dual-V groove microchannels geometry was developed and combined with a tapered open manifold to achieve significant performance enhancements in all three aspects while reporting boiling inversion for the first time in flow boiling. Evaporation momentum force is utilized to direct bubbles along a central region of the doubly-finned structure, while inertia force is utilized to create a two-phase flow in the microchannel flow passages formed by the fins. The microchannel passages are contoured as adjoining pairs of asymmetric Dual-V grooves. Bubbles nucleate at the corners of the V-grooves and the evaporation momentum force modulates their traverse over the inclined surfaces of the microchannels. High-speed video images reveal that the growing bubbles flow rapidly over the microchannel walls and emerge into the microgap region a certain distance away from their respective nucleation sites. This leads to a self-feeding mechanism that causes boiling inversion in which wall superheat drops with increase in heat flux. Early departure from the nucleation site before fully growing improves the CHF and the bubble traverse normal to flow direction improves HTC. Furthermore, the momentum of the growing bubbles in the tapered open microgap configuration reduces the pressure drop. Using water as working fluid, we have reached a heat dissipation of 508.1 W/cm2 without reaching CHF at a wall superheat of 12.3 °C with a pressure drop of only 3 kPa. The resulting HTC was 412.2 kW/(m2 K).

Dynamics and bifurcations of non-Newtonian Au–Cu/blood hybrid nanofluid model of electrokinetic flow in asymmetrically tapered wave microchannel

The present paper investigates the dynamic behavior of streamline patterns with their bifurcations for heat transfer in a peristaltic flow model. This model represents an incompressible Casson hybrid nanofluid Au–Cu/blood flowing through a porous saturated tapered asymmetric microchannel in the presence of electroosmotic body force, velocity slip, and temperature jump conditions. Analytical and numerical tools are used to perform a thorough bifurcation and stability analysis of the various stagnation point positions. The global dynamics behavior around these points generates invariant sets and attractors, such as a surface of heteroclinic connections between saddle stagnation points, which is used to predict the various flow modes and topologies that control stream flow. The impact of the physical parameters associated with flow problems is also thoroughly investigated and graphically illustrated.

Discrimination of tumor cell type based on cytometric detection of dielectric properties

In this paper, a microfluidic impedance cytometer (MIC) was employed to analyze the dielectric properties of human white blood cells (WBCs) and four tumor cell lines and realize the label-free identification of cell types. The impedance of cells was detected using an asymmetric serpentine microchannel based MIC under four different frequencies simultaneously. The asymmetric serpentine microchannel achieved the elasto-inertial focusing of cells into a single train, ensuring accurate impedance detection of cells. Various dielectric parameters (cell diameters, impedance amplitude |Z|, impedance phase shift ΦZ, and electric opacities |Z|HF/|Z|LF, ΦZHF/ΦZLF, Re(ZHF)/Re(ZLF), and Im(ZHF)/Im(ZLF)) were defined and used to analyze the dielectric properties of cells. The obtained dielectric parameters were used to train machine learning classification models for identifying cell types. Using all parameters proposed in this paper (cell diameter, opacity |Z|HF/|Z|LF, ΦZHF/ΦZLF, Re(ZHF)/Re(ZLF), and Im(ZHF)/Im(ZLF)) to train the classification model, the true positive rate (TPR) for the identification of WBCs, A549, MCF7, H226, and H460 cells were 99.6%, 96.2%, 99.1%, 97.6%, and 97.2%, respectively. Results showed that our MIC provided a promising method for label-free discrimination of circulating tumor cells in multiple primary cancers.

Distribution of liquid-liquid two-phase flow and droplet dynamics in asymmetric parallel microchannels

The numbering-up of microchannels in parallel is usually engineered to achieve high-throughput production of droplets, and the flow distribution of fluids and uniformity of droplets in parallel microchannels are core issues for droplet formation. In this work, the distribution of liquid–liquid two-phase flow and droplet dynamics in asymmetric parallel microchannels are investigated by using a high speed camera, and the factors affecting the stability and uniformity of droplets are explored. The dynamic behavior of droplet swarm in the rear cavity and its feedback effect on droplet generation at T-junctions are revealed. The microfluidic devices with various configurations are designed to investigate its effects on flow distribution. In addition, based on the principle of hydrodynamic resistance for the liquid-liquid two-phase flow in microchannels, the prediction for the distribution of liquid-liquid two-phase flow under slug flow is proposed.

Analysis of thermal radiation, Joule heating, and viscous dissipation effects on blood‐gold couple stress nanofluid flow driven by electroosmosis

AbstractGold nanoparticles associated with DNA, RNA, proteins, oligonucleotides, and peptides are useful in therapies and drug delivery. The present article mainatins that gold nanoparticles play a tremendous role in remedying cancer and fatal diseases. A mathematical model is proposed for the two‐dimensional motion of the couple stress nanofluid consisting of gold nanoparticles under the application of peristaltic propulsion and electroosmosis mechanisms in an asymmetric microchannel. The effects of radiation with slip boundary have been employed. The governing equations are simplified under the assumptions of low Reynolds number and long wavelength and the Poisson‐Boltzmann equation is solved under Debye–Hückel linearization. Analytical solutions for the velocity of fluid motion, nanoparticle temperature, stream function, pressure gradient, are evaluated and analyzed graphically under the effects of various physical parameters. It is notable from the analysis that raising the Brinkman number boosts the nanoparticle temperature and heat transfer coefficient which validate the physical model and analysis. Moreover, it is noticed that sphere‐shaped gold nanoparticles enhance the temperature as compared to other geometries of nanoparticles. The present study results may assist in developing the technology, smart micropumps, drugs, and device for hemodialysis and other health care applications.

Peristaltic flow of electrically conducting nanofluid under the action of Joule and radiative heat within an asymmetric microchannel

The proposed mathematical model is based upon the peristaltic flow of an electrical conducting nanofluid within an asymmetric microchannel. The flow takes place under the action of dissipative heat energy due to the occurrence of the magnetic field that is basically known as Joule heating and radiative heat proposed as thermal radiation along with the additional heat source. Moreover, the impact of upper/lower wall zeta potential and the expression for the electric potential is presented using the Poisson Boltzmann equation and Debey length approximation. The well-known numerical practice is used for distorted governing equations with appropriate boundary conditions. Further, computation of the pressure gradient is obtained for the associated physical parameters. The graphical illustration shows the characteristics of the pertinent parameters on the flow problem and the tabular result represents the simulated values for the rate coefficients. In the significant examination, the study reveals that the mobility parameter due to the occurrence of the electric field vis-à-vis time parameter encourages the velocity distribution within the center of the channel furthermore significant retardation occurs near the wall region.

Flow Boiling of R1336mzz(Z) in Tapered Microgaps with Asymmetric Dual-V Microchannels

Flow Boiling of R1336mzz(Z) in Tapered Microgaps with Asymmetric Dual-V Microchannels

EMHD creeping rheology of nanofluid through a micro-channel via ciliated propulsion under porosity and thermal effects

The mathematical study is modeled to examine the physical impacts of porosity and thermal slip on flow features of nanofluid through an asymmetric micro-channel. Additionally, the effects of electro-osmosis and magnetic field are also under consideration. Convective boundary conditions are used in the current study by neglecting thermal and buoyancy forces. The obtained rheological equations are transformed into non-dimensional flow systems by using scaling variables. These rheological equations are elucidated by using the creeping approximation and low zeta potential (the Debye–Hückel linearization). The exact solutions of rheological equations are evaluated via Mathematica software 11.0. The dynamic impacts of embedded parameters such as Hartmann number, electro-osmosis parameter, Darcy's number, Brinkman number, Helmholtz–Smoluchowski velocity, slip parameter, thermal radiation, cilia length parameter and Prandtl number on the rheological features are presented graphically via Mathematica software 11.0. The whole analysis is based upon train waves of metachronal propulsion. Three-dimensional graphs are plotted in the current investigation to get more obvious behavior of embedded on the flow features. The cilia length parameter has a remarkable character in enhancing the magnitude of velocity profiles, while, and opposite actions is perceived in the graph of pressure gradient. The thermal slip parameters have an energetic impact in reducing the temperature profile magnitude. The outcomes revealed a good understanding into biomimetic energy frameworks taking advantage of electroosmosis, magnetism and nanotechnology, and, besides, they outfit a valuable benchmark for numerical and experimental multi-physics recreations.

Numerical study of droplet breakup in an asymmetric T-junction microchannel with different cross-section ratios

In this study, numerical simulations are conducted to investigate droplet breakup in an asymmetric [Formula: see text]-junction microchannel with different cross-section ratios. To this approach, a two-phase model based on the volume of fluid (VOF) method is adopted to study the three-dimensional feature of droplet motion inside [Formula: see text]-junctions. The comparison reveals that the present results are in good agreement with previous studies. The effects of the capillary number (Ca), the non-dimensional droplet length ([Formula: see text]), and the non-dimensional width ratio ([Formula: see text]) on the breakup time and splitting ratio of daughter droplets are studied. Five distinct regimes are observed involving the non-breakup, breakup with tunnel, breakup without tunnel, asymmetric breakup, and sorting. Achieved results indicate that the time of breakup ([Formula: see text]) increases about 15% when the Ca is increased from 0.0134 to 0.0268 (about 100%). It is also found that the mass center of the mother droplet in the primary channel is shifted to a larger wide branch, which facilitates the asymmetric breakup of the droplet in a [Formula: see text]-junction microchannel.

Hydrothermal performances of symmetric and asymmetric divergent-convergent microchannel heat sinks

The present work numerically studied the hydrothermal performance of symmetric and asymmetric divergent-convergent microchannel heat sink (DCMCHS) with the rectangular cross-section. Three different DCMCHS with fixed total channel volume were designed, the symmetric DCMCHS, the width-asymmetric DCMCHS with the fixed inlet-to-middle cross-sectional width ratio, and the width-asymmetric DCMCHS with the fixed middle cross-sectional width. Effects of the inlet-to-middle cross-sectional width ratio and channel height of the symmetric DCMCHS, and the outlet-to-inlet width ratio, the middle cross-sectional width and the channel height of the width-asymmetric DCMCHSs on the maximum temperature, overall thermal resistance, pressure drop, and the coefficient of performance (COP) of the DCMCHSs were analyzed. It was found that the symmetric DCMCHS with smaller inlet-to-middle width ratio has smaller thermal resistance but larger pressure drop. Moreover, the decreasing outlet-to-inlet width ratio can improve the thermal performance of the two width-asymmetric DCMCHSs and increase the pressure drop. The increasing middle cross-sectional width can reduce the thermal resistance of width-asymmetric DCMCHS with fixed channel height and fixed outlet-to-inlet width ratio by consuming more pressure drop. For the COP, all the proposed DCMCHSs in the present work have smaller COP compared with the conventional parallel MCHS.

Asymmetric serpentine microchannel based impedance cytometer enabling consistent transit and accurate characterization of tumor cells and blood cells

A consistent cell transit position is essential for accurately characterize cellular impedance signature. In this paper, we integrated asymmetric serpentine structure and elasto-inertial focusing methods to manipulate cells’ special transit position horizontally and vertically, and minimize the fluctuation of impendence responses at multiple excitation frequencies. The asymmetric serpentine structure is capable to rapidly align randomly distributed particles into a single stream horizontally, and the addition of hyaluronic acid (HA) in the sample fluid enables cells to focus in a single train in a wide range of flow rate. In the experiment section, we evaluated the alignment accuracy of asymmetric serpentine microchannel using standard particles ranging from 7 to 20 μm to mimic tumor cells. Compared with randomly distributed and dually aligned particles, the coefficient of variation (CV) of the impedance of particles is markedly reduced. To further prove this device can differentiate various cells, we tested breast tumor cells (MCF7), non-small lung tumor cells (A549) and white blood cells. Based on their electrical impedance signature including opacity and phase shift, a machine learning algorithm was used to identify cell types. This device is able to differentiate MCF7 cells with an accuracy of 95 % and differentiate A549 cells with an accuracy of 92.3 %. This device is able to efficiently focus tumor cells without sheath flow and accurately detect tumor cells, it has a great potential to discriminate, count and phenotype rare circulating tumor cells in patients’ blood.

Experimental Platform to Study Spiking Pattern Propagation in Modular Networks In Vitro.

The structured organization of connectivity in neural networks is associated with highly efficient information propagation and processing in the brain, in contrast with disordered homogeneous network architectures. Using microfluidic methods, we engineered modular networks of cultures using dissociated cells with unidirectional synaptic connections formed by asymmetric microchannels. The complexity of the microchannel geometry defined the strength of the synaptic connectivity and the properties of spiking activity propagation. In this study, we developed an experimental platform to study the effects of synaptic plasticity on a network level with predefined locations of unidirectionally connected cellular assemblies using multisite extracellular electrophysiology.

A passive Stokes flow rectifier for Newtonian fluids

Non-linear effects of the Navier–Stokes equations disappear under the Stokes regime of Newtonian fluid flows disallowing a flow rectification behavior. Here we show that passive flow rectification of Newtonian fluids is obtainable under the Stokes regime of both compressible and incompressible flows by introducing nonlinearity into the otherwise linear Stokes equations. Asymmetric flow resistances arise in shallow nozzle/diffuser microchannels with deformable ceiling, in which the fluid flow is governed by a non-linear coupled fluid–solid mechanics equation. The proposed model captures the unequal deflection profile of the deformable ceiling depending on the flow direction under the identical applied pressure, permitting a larger flow rate in the nozzle configuration. Ultra-low aspect ratio microchannels sealed by a flexible membrane have been fabricated to demonstrate passive flow rectification for low-Reynolds-number flows (0.001 < Re < 10) of common Newtonian fluids such as water, methanol, and isopropyl alcohol. The proposed rectification mechanism is also extended to compressible flows, leading to the first demonstration of rectifying equilibrium gas flows under the Stokes flow regime. While the maximum rectification ratio experimentally obtained in this work is limited to 1.41, a higher value up to 1.76 can be achieved by optimizing the width profile of the asymmetric microchannels.

Electro-osmatic flow of Jeffrey fluid in an asymmetric micro-channel under the effect of Magnetic field

In this article, we have investigated the peristaltic transport of electro-osmotic flow of Jeffrey fluid in an asymmetric channel, in which the walls are modulated by the peristaltic array of patches. In the presence of Electrical Debye Layer (EDL), the Poisson Boltzmann equation for the electrical potential within the micro channel is considered. To evaluate the electrical potential, Debye-Huckel linearization is employed the governing equations are modeled and reduce by small Reynolds number and long wavelength approximation and solved the exact solution. The axial fluid velocity, temperature, pressure gradient, pressure rise and stream functions are discussed with the effects of pertinent parameters (Hartmann number, Phase angle, relaxation time parameter) through the graphs.

Heat and Mass Transfer of a Peristaltic Electro-osmotic Flow of a Couple Stress Fluid through an Inclined Asymmetric Channel with Effects of Thermal Radiation and Chemical Reaction

The presented article addresses the electro-osmotic peristaltic flow of a couple stress fluid bounded in an inclined asymmetric micro-channel. The viscous dissipation, Joule heating and chemical reaction effects are employed simultaneously in the flow analysis. Heat and mass transfer have been studied under large wavelength and small Reynolds number. The resulting nonlinear systems are solved numerically. The influence of various dominant physical parameters is discussed for velocity, temperature distribution, concentration distribution and the pumping characteristics. Electro kinetic flow of fluids by micro-pumping through micro channels and micro peristaltic transport has accelerated considerable concern in accelerated medical technology and several areas of biomedical engineering. Deeper clarification of the fluid dynamics of such flow requires the continuous need for more delicate mathematical models and numerical simulations, in parallel with laboratory investigations.