Microfluidic Dynamics Research Articles

Optimization design and simulation of chip-level micro-gas columnar preconcentrator structure based on ANSYS

Abstract To achieve the efficient preconcentration of measured sample gas in microfluidic chips, this paper proposes a design and simulation scheme for the chip-level micro-gas columnar pre-concentrated structure based on ANSYS software. Firstly, four kinds of chip-level micro-gas columnar preconcentrators with circular, semi-circular, triangular, and rhombic shapes were designed, and the simulation analysis of gas-phase micro-fluidic dynamics was performed on the chip-level micro-gas columnar preconcentrator by ANSYS software. The influence of different design parameters on the pre-concentrated effect of level chips micro-gas columnar preconcentrator was discussed. The simulation results show that the arrangement is a triangle arranged in reverse parallel, and the preconcentration effect of the chip-level micro gas column preconcentrator is better.

Electroosmotic microchannel flow of blood conveying copper and cupric nanoparticles: Ciliary motion experiencing entropy generation using backpropagated networks

AbstractA novel mathematical model for a hybrid (Cu–CuO/blood) Jeffrey nanofluid passing a vertical symmetric microchannel along with an electroosmosis pump is presented. The focuses on the advancement of mathematical modeling techniques, its comprehensive analysis of microfluidic system dynamics, and its potential to inform the optimal design of devices using nanofluids with broad applications in various fields. Arrhenius's law is used to analyze endothermic–exothermic reactions and activation energy. The governing partial differential equations of the fixed frame are transformed into ordinary differential equations of the wave frame using self‐similarity transformations. Low Reynolds number and long‐wavelength approximations helped to find solutions of the equations by applying a suitable BVP solver in MATLAB. The fluid's velocity, temperature, concentration, and electroosmosis properties are studied graphically. Two‐dimensional contour plots of fluid velocity and three‐dimensional surface plots of fluid properties are discussed. Physically significant quantities of mass transfer rate, skin friction coefficient, entropy generation, and heat transfer rate are studied using contour plots. Artificial neural network simulation using Bayesian regularization backpropagation algorithms is analyzed for training state, error histogram, fit, performance, and regression plots. Conclusively, the comprehensive analysis of the fluid dynamics, entropy generation, mass and heat transfer, and in the microchannel, coupled with the successful implementation of artificial neural network simulation, contributes to an improved understanding of the system's behavior. Entropy generation was raised for enhanced Brownian motion number and reduced values of thermophoresis, activation energy, and endothermic–exothermic reaction parameters. This study's results can be used to improve the efficiency and effectiveness of microfluidic devices used in fields as diverse as electrical cooling and medicine delivery.

Integrating electric double layer time-varying and dual interface slip for predicting migration behavior of moisture and ions

Migration of moisture and chloride ions in calcium-silicate-hydrates (C-S-H) nanopores is important factor for controlling the durability of concrete and affecting the physical and chemical properties of cement-based binder. Quantitative analysis of experimental results indicates that the pore in C-S-H is mainly distributed on the nanometer scale. Due to the prominent interfacial effects at the nanoscale, moisture and ions in different regions within nanochannels exhibit distinct molecular structures and dynamic properties. Therefore, the wetting behavior of the synthesized C-S-H surface and its influence on microfluid dynamics analysis and boundary condition definition were systematically analyzed based on the contact angle experiment. Statistical thermodynamics were introduced to describe the time-varying characteristics of the electric double layer (EDL). With the interaction as the theoretical framework and interaction energy as an important parameter, the equilibrium behavior of interacting particles was studied to describe the stability of EDL system. The flow control equation and boundary conditions were modified considering the action of EDL. The transport model of moisture and chloride ions under the combined influence of electric double layer and dual interface slip was proposed. The results show that the existence of EDL impedes the movement of the fluid, while the dual slippage of water film and time-varying of EDL reduce the resistance. Quantitative analysis indicates the contribution ratios of water film slip and EDL time-varying can reach 85% and 29%, respectively. In addition, water film slip has a greater influence on water migration and EDL time-varying has a greater influence on ions. This research can provide new insights into the transport mechanism of water and chloride ions at micro-nanoscale.

Optofluidic transport and assembly of nanoparticles using an all-dielectric quasi-BIC metasurface

Manipulating fluids by light at the micro/nanoscale has been a long-sought-after goal for lab-on-a-chip applications. Plasmonic heating has been demonstrated to control microfluidic dynamics due to the enhanced and confined light absorption from the intrinsic losses of metals. Dielectrics, the counterpart of metals, has been used to avoid undesired thermal effects due to its negligible light absorption. Here, we report an innovative optofluidic system that leverages a quasi-BIC-driven all-dielectric metasurface to achieve subwavelength scale control of temperature and fluid motion. Our experiments show that suspended particles down to 200 nanometers can be rapidly aggregated to the center of the illuminated metasurface with a velocity of tens of micrometers per second, and up to millimeter-scale particle transport is demonstrated. The strong electromagnetic field enhancement of the quasi-BIC resonance increases the flow velocity up to three times compared with the off-resonant situation by tuning the wavelength within several nanometers range. We also experimentally investigate the dynamics of particle aggregation with respect to laser wavelength and power. A physical model is presented and simulated to elucidate the phenomena and surfactants are added to the nanoparticle colloid to validate the model. Our study demonstrates the application of the recently emerged all-dielectric thermonanophotonics in dealing with functional liquids and opens new frontiers in harnessing non-plasmonic nanophotonics to manipulate microfluidic dynamics. Moreover, the synergistic effects of optofluidics and high-Q all-dielectric nanostructures hold enormous potential in high-sensitivity biosensing applications.

Phase image correlation spectroscopy for detecting microfluidic dynamics.

It is essential to quantify the physical properties and the dynamics of flowing particles in many fields, especially in microfluidic-related applications. We propose phase image correlation spectroscopy (PICS) as a versatile tool to quantify the concentration, hydro-diameter, and flow velocity of unlabeled particles by correlating the pixels of the phase images taken on flowing particles in a microfluidic device. Compared with conventional image correlation spectroscopy, PICS is minimally invasive, relatively simple, and more efficient, since it utilizes the intrinsic phase of the particles to provide a contrast instead of fluorescent labeling. We demonstrate the feasibility of PICS by measuring flowing polymethylmethacrylate (PMMA) microspheres and yeast in a microfluidic device. We can envisage that PICS will become an essential inspection tool in biomedicine and industry.

Long‐Range‐Ordered Assembly of Micro‐/Nanostructures at Superwetting Interfaces

On-chip integration of solution-processable materials imposes stringent and simultaneous requirements of controlled nucleation and growth, tunable geometry and dimensions, and long-range-ordered assembly, which is challenging in solution process far from thermodynamic equilibrium. Superwetting interfaces, underpinned by programmable surface chemistry and topography, are promising for steering transport, dewetting, and microfluid dynamics of liquids, thus opening a new paradigm for micro-/nanostructure assembly in solution process. Herein, assembly methods on the basis of superwetting interfaces are reviewed for constructing long-range-ordered micro-/nanostructures. Confined capillary liquids, including capillary bridges and capillary corner menisci realized by controlling local wettability and surface topography, are highlighted for simultaneously attained deterministic patterning and long-range order. The versatility and robustness of confined capillary liquids are discussed with assembly of single-crystalline micro-/nanostructures of organic semiconductors, metal-halide perovskites, and colloidal-nanoparticle superlattices, which lead to enhanced device performances and exotic functionalities. Finally, a perspective for promising directions in this realm is provided.

Numerical study of microfluidic emulsion dynamics under the influence of heterogeneous surface wettability

Surface wettability plays a vital role in various natural phenomena and technical applications, such as coating, printing, membrane technology, microfluidic devices, and porous media flow. We numerically investigate the dynamics and stability of liquid–liquid dispersion flowing in a microfluidic channel with heterogeneous surface wettability, using a conservative phase-field lattice Boltzmann method. First, we validate the implementation of the wetting boundary conditions. We then perform three-dimensional simulations of a single drop motion immersed in another immiscible liquid in a square microchannel with alternating surface wettability: hydrophilic, hydrophobic, and again hydrophilic sections. The viscosity of the dispersed liquid (oil) is ten times higher than that of the continuous one (water), while the two liquids have equal densities. Depending on the drop length and Capillary number, calculated based on the drop velocity and the dynamic viscosity of the continuous phase, four different flow patterns are observed when the drop passes through the hydrophobic section. The distinct flow patterns include passing without any changes in drop shape or dynamics, adhesion of the dispersed liquid to the walls, phase inversion (i.e., water becomes the dispersed phase), and drop breakage. These outcomes are in close agreement with the experimental data. A detailed explanation of the choice of the numerical parameters is presented. The critical aspect of capturing the observed drop behavior is introducing an intervening thin-film of the continuous phase of at least three diffuse interface thicknesses (between the drop and channel walls).

Human Nonalcoholic Steatohepatitis on a Chip.

Nonalcoholic steatohepatitis (NASH), an advanced stage of nonalcoholic fatty liver disease (NAFLD), is a rapidly growing and global health problem compounded by the current absence of specific treatments. A major limiting factor in the development of new NASH therapies is the absence of models that capture the unique cellular structure of the liver microenvironment and recapitulate the complexities of NAFLD progression to NASH. Organ-on-a-chip platforms have emerged as a powerful approach to dynamically model diseases and test drugs. Herein, we describe a NASH-on-a-chip platform. Four main types of human primary liver cells (hepatocytes [HCs], Kupffer cells, liver sinusoidal endothelial cells, and hepatic stellate cells [HSCs]) were cocultured under microfluidic dynamics. Our chip-based model successfully recapitulated a functional liver cellular microenvironment with stable albumin and urea secretion for at least 2weeks. Exposing liver chips to a lipotoxic environment led to gradual development of NASH phenotypic characteristics, including intracellular lipid accumulation, hepatocellular ballooning, HSC activation, and elevation of inflammatory and profibrotic markers. Further, exposure of the chip to elafibranor, a drug under study for the therapy of NASH, inhibited the development of NASH-specific hallmarks, causing an ~8-fold decrease in intracellular lipids, a 3-fold reduction in number of ballooned HCs, a significant reduction in HSC activation, and a significant decrease in the levels of inflammatory and profibrotic markers compared with controls. Conclusion: We have successfully developed a microfluidic NASH-on-a-chip platform that recapitulates the main NASH histologic endpoints in a single chip and that can emerge as a powerful noninvasive, human-relevant, in vitro platform to study disease pathogenesis and develop novel anti-NASH drugs.

Microfluidic Templating: Microfluidic Templating of Spatially Inhomogeneous Protein Microgels (Small 32/2020)

In article number 2000432, Tuomas P. J. Knowles and co-workers demonstrate a simple microfluidic approach to produce spatially inhomogeneous protein microgels, using versatile crosslinking regimes and microfluidic dynamics under biocompatible conditions. The microgels are promising candidates for extracellular matrix analogues and tissue engineering scaffolds, which could open up new possibilities of micron-scaled constructs at the frontiers of engineering/biology/materials interfaces.

Optimizing Brownian escape rates by potential shaping

Brownian escape is key to a wealth of physico-chemical processes, including polymer folding and information storage. The frequency of thermally activated energy barrier crossings is assumed to generally decrease exponentially with increasing barrier height. Here, we show experimentally that higher, fine-tuned barrier profiles result in significantly enhanced escape rates, in breach of the intuition relying on the above scaling law, and address in theory the corresponding conditions for maximum speed-up. Importantly, our barriers end on the same energy on which they start. For overdamped dynamics, the achievable boost of escape rates is, in principle, unbounded so that the barrier optimization has to be regularized. We derive optimal profiles under 2 different regularizations and uncover the efficiency of N-shaped barriers. We then demonstrate the viability of such a potential in automated microfluidic Brownian dynamics experiments using holographic optical tweezers and achieve a doubling of escape rates compared to unhindered Brownian motion. Finally, we show that this escape rate boost extends into the low-friction inertial regime.

Superwettability-Based Interfacial Chemical Reactions.

Superwetting interfaces arising from the cooperation of surface energy and multiscale micro/nanostructures are extensively studied in biological systems. Fundamental understandings gained from biological interfaces boost the control of wettability under different dimensionalities, such as 2D surfaces, 1D fibers and channels, and 3D architectures, thus permitting manipulation of the transport physics of liquids, gases, and ions, which profoundly impacts chemical reactions and material fabrication. In this context, the progress of new chemistry based on superwetting interfaces is highlighted, beginning with mass transport dynamics, including liquid, gas, and ion transport. In the following sections, the impacts of the superwettability-mediated transport dynamics on chemical reactions and material fabrication is discussed. Superwettability science has greatly enhanced the efficiency of chemical reactions, including photocatalytic, bioelectronic, electrochemical, and organic catalytic reactions, by realizing efficient mass transport. For material fabrication, superwetting interfaces are pivotal in the manipulation of the transport and microfluidic dynamics of liquids on solid surfaces, leading to the spatially regulated growth of low-dimensional single-crystalline arrays and high-quality polymer films. Finally, a perspective on future directions is presented.

Toward a mechanistic understanding of microfluidic droplet-based extraction and separation of lanthanides

Droplet-based microfluidic extraction is a promising way for effective lanthanides extraction due to its outstanding mass transfer performance. The separation process can be greatly enhanced with the droplet-based microfluidic extraction technique. However, the interactions between mass transfer, microfluidic dynamics and extraction kinetics are still unclear, which has hindered further manipulation on microfluidic extraction to boost extraction performance. In this study, the mechanisms of microfluidic droplet-based extraction and separation intensification of lanthanides are for the first time unveiled by using a numerical simulation model. The limiting factors for the performance of droplet-based microfluidic extraction are identified through a model-based parametric analysis. The numerical analyses provide a comprehensive understanding of droplet-based microfluidic extraction systems and offer operation and optimization guidelines for future research in this area.

Non-Uniform Laser Surface Texturing of an Un-Tapered Square Pad for Tribological Applications

Femtosecond laser surface micro-texturing has emerged as a promising technology to enhance the tribological properties of different kinds of electromechanical devices. In this research paper, we have exploited the intrinsic flexibility and micrometric accuracy of femtosecond laser ablation to realize complex micro-structural modifications on the surface of a laboratory prototype of a steel thrust bearing (un-tapered) pad. The Bruggeman Texture Hydrodynamics theory (BTH) is employed for the design of the anisotropic and non-uniform texture maximizing the thrust load of the pad prototype. The preliminary experimental results, reported in this work, show that the non-uniform micro-texture largely affects the friction characteristics of the contact. In particular, in agreement with the BTH predictions, the tribo-system shows friction properties that are strongly sensitive to the direction of the sliding speed, as a consequence of the micro-fluid dynamics which are designed to occur only in a specific sliding direction. We suggest that the joint action of virtual prototyping (BTH lubrication theory) and ultrafast laser micro-prototyping can lead to unconventional and impressive results in terms of enhanced or tailored contact mechanics properties of the generic lubricated tribopair.

Experimental investigation of micro-channels produced in aluminum alloy (AA 2024) through laser machining

Aluminum and its alloys are growingly used in various applications including micro-channel heat exchangers and heat sinks to facilitate heat transfer though micro-fluidic flows. Micro-channels with precise control over geometrical features are very important in order to design micro-fluidic flow dynamics and its characteristics. In this research, Nd:YAG laser beam micro-milling has been utilized to produce micro-channels in aluminum alloy (AA 2024) having cross-sectional size of 400 × 200 µm2. The objective was to control the material removal rate (MRR) of the process in order to get the micro-channels’ geometries (width, depth and taperness of sidewalls) close to the designed geometries. In this context, parametric effects of predominant laser parameters on the process performance have been categorically studied. Quadratic mathematical models have further been developed to estimate the MRR and each geometrical aspect of micro-channels over different levels of laser parameters. Additionally, multi-objective optimization has been performed to get an optimized set of laser parameters generating the accurate machining geometries with appropriate material removal per laser scan. Finally, the models and optimization results were validated through confirmatory experimental tests. The results reveal that the precised micro-channel geometries can be obtained through laser beam micro-milling by selecting the appropriate combination of laser parameters (lamp current intensity of 84.48 %, laser pulse frequency of 35.70 kHz and laser scanning speed of 300 mm/s) that can collectively remove a required amount of material thickness per laser scan.

Qualitative and quantitative analyses of stroke dynamics and microfluidics of phacoemulsification probes operating in different modes

To compare phacoemulsification (phaco) tip movement, microfluidic dynamics, and tip-to-load interaction between longitudinal, torsional, and elliptical ultrasound (US) modalities. Phacodynamics Laboratory, Clínica Oftalmológica, Pasteur, Santiago, Chile. Experimental study. All experiments were performed using a fluid-filled optical test chamber and phaco tips that were US power activated. Tip movement was evaluated using stroke tracing and stroboscopy imaging techniques. Qualitative and quantitative assessments of microfluidic behavior were performed using bead seeding and high-speed shadowgraphy imaging combined with particle-image velocimetry and vector analysis. Material load interaction was measured using a rubber sphere that represented lens material. Longitudinal and torsional US tips showed precise forward-and-backward and side-to-side (lateral) movement, respectively. Elliptical US tips scribed a 2-dimensional ellipsoid path that slightly changed in shape and orientation plane at higher powers. Longitudinal and lateral components of tip motion were evident in elliptical mode. Regular fluid flow was observed with longitudinal mode (forward-directed flow away from the aspiration port) and torsional mode (steady backflow into the aspiration port). In elliptical mode, bead repulsion, erratic bursts of acoustic streaming, oblique backflow, and areas of multidirectional flow were observed. The longitudinal mode caused the material load to bounce against the tip, whereas the torsional mode maintained a consistent load attraction. In elliptical mode, the material load rotated slightly and bounced away from the tip in irregular intervals when attraction was achieved. Tip movement, microfluidic behavior, and material load interaction were related within but varied across US modalities. The elliptical mode showed a movement pattern with longitudinal and lateral components and irregular microfluidic behaviors. Dr. Zacharias received research funding from Alcon Laboratories, Inc. He has no financial or proprietary interest in any material or method mentioned.

Optofluidic bioimaging platform for quantitative phase imaging of lab on a chip devices using digital holographic microscopy

We propose a versatile 3D phase-imaging microscope platform for real-time imaging of optomicrofluidic devices based on the principle of digital holographic microscopy (DHM). Lab-on-chip microfluidic devices fabricated on transparent polydimethylsiloxane (PDMS) and glass substrates have attained wide popularity in biological sensing applications. However, monitoring, visualization, and characterization of microfluidic devices, microfluidic flows, and the biochemical kinetics happening in these devices is difficult due to the lack of proper techniques for real-time imaging and analysis. The traditional bright-field microscopic techniques fail in imaging applications, as the microfluidic channels and the fluids carrying biological samples are transparent and not visible in bright light. Phase-based microscopy techniques that can image the phase of the microfluidic channel and changes in refractive indices due to the fluids and biological samples present in the channel are ideal for imaging the fluid flow dynamics in a microfluidic channel at high resolutions. This paper demonstrates three-dimensional imaging of a microfluidic device with nanometric depth precisions and high SNR. We demonstrate imaging of microelectrodes of nanometric thickness patterned on glass substrate and the microfluidic channel. Three-dimensional imaging of a transparent PDMS optomicrofluidic channel, fluid flow, and live yeast cell flow in this channel has been demonstrated using DHM. We also quantify the average velocity of fluid flow through the channel. In comparison to any conventional bright-field microscope, the 3D depth information in the images illustrated in this work carry much information about the biological system under observation. The results demonstrated in this paper prove the high potential of DHM in imaging optofluidic devices; detection of pathogens, cells, and bioanalytes on lab-on-chip devices; and in studying microfluidic dynamics in real time based on phase changes.

Numerical Simulation Research of an Ultra-Micro Dispensing

Along with the miniaturization of products and the precision of micro-assembly, the ultra-micro dispensing is an important guarantee to realize precision assembly. In this paper, we analyze the dynamic process of an ultra-micro (fLclass) dispensing based on the micro-droplet surface tension. According to the analysis, the micro-fluid dynamics model is built in the CFD (Computational Fluid Dynamics) software Fluent14.0 program, and the working process is dynamically simulated based on the model. Furthermore, the experiment platform is established and actual dispensing process similar to the simulation is successfully acquired under the same conditions. Finally, the diameters of actual dispensing dots are compared with simulation values respectively under the same three sets of different dispensing parameters, and results show that actual values keep high consistency with the simulations, which verifies the correctness and feasibility of the proposed micro-fluid dynamics model.

Multiplex Particle Focusing via Hydrodynamic Force in Viscoelastic Fluids

We introduce a multiplex particle focusing phenomenon that arises from the hydrodynamic interaction between the viscoelastic force and the Dean drag force in a microfluidic device. In a confined microchannel, the first normal stress difference of viscoelastic fluids results in a lateral migration of suspended particles. Such a viscoelastic force was harnessed to focus different sized particles in the middle of a microchannel, and spiral channel geometry was also considered in order to take advantage of the counteracting force, Dean drag force that induces particle migration in the outward direction. For theoretical understanding, we performed a numerical analysis of viscoelastic fluids in the spiral microfluidic channel. From these results, a concept of the ‘Dean-coupled Elasto-inertial Focusing band (DEF)' was proposed. This study provides in-depth physical insight into the multiplex focusing of particles that can open a new venue for microfluidic particle dynamics for a concrete high throughput platform at microscale.

Nano and micro-scale fluid and plasma dynamics: present and future applications

In this letter, we illustrate the importance of fluid dynamics research by considering two particular areas of study: nano- and micro-scale fluid and plasma dynamics. We show how improved scientific knowledge of nano- and micro-fluid dynamics can significantly enhance our future. Application is also discussed regarding environmental aspects.

Microfluidic-Assisted Fabrication of Nanoparticles for Nanomedicine Application

This article provided an overview of recent patents on microfluidic-assisted fabrication of nanoparticles and their applications for nanomedicine. Microfluidic dynamics was predominantly characterized by laminar flow due to the small dimensions involved, which resulted in unique fluid morphologies and the production of polymer particles with an improved control over their sizes, size distributions, morphologies, and compositions. We compared capillary-based microsystem and microchannel-based microsystem, and presented novel structural improvements on microchips. New developments in microfabrication techniques provided complex, compact and highly integrated platforms that might produce more complex droplets. Advanced technologies and integrating or modular design may push the microchannelbased microsystem toward novel mutilfunctionalization to realize bio-encapsulation, transportation, mixing or injection, screening, and detection for biomedicine purpose. In the near future, the microchannel-based microsystem might function as not only the assay platforms, but also the implantable devices to monitor on-line. Keywords: Droplets, nanoparticles, microfluidic, capillary-based microsystem, microchannel-based microsystem, T-junction, flow focusing, emulsification, solidification, monodisperse, fusion, fluid transportation, mixing, detection, screening, Microfluidic-assisted fabrication, nanomedicine application, bio-encapsulation