Design Of Microfluidic Devices Research Articles

Saturation Equation: An Analytical Expression for Partial Saturation during Wicking Flow in Paper Microfluidic Channels.

The design and fabrication of paper-based microfluidic devices is critically dependent on modeling fluid flow through porous paper membranes. A commonly observed phenomenon is partial saturation, i.e., regions of the paper membrane not being filled completely due to pores of different sizes. The most comprehensive model to date of partial saturation during wicking flow in paper is the Richards equation. However, the solution to the Richards equation requires numerical solvers like COMSOL, which makes it largely inaccessible to the paper microfluidics and lateral flow assay community. There is therefore a need for a simple and appropriate model of partial saturation in paper membranes, easily usable by the wider research community. In the current work, we present an approach to model paper membranes as a bundle of parallel capillaries whose radii follow a two-parameter log-normal distribution. Application of the Washburn equation to the bundle provides a distribution of fluid fronts, which can be used to calculate saturation. Using this approach, we developed the "saturation equation"─an explicit analytical expression to calculate saturation as a function of space and time in 1D wicking flow. Experimentally obtained data for spatiotemporal saturation for four different paper materials were fit to this analytical model to obtain parameters for each material. Results obtained from this analytical model match well with both experimental data and numerical results obtained from the Richards equation. The availability of an explicit analytical expression for partial saturation will enable incorporation of the critical phenomenon of partial saturation in the design of paper microfluidic devices.

Exploring microrotational effects and temperature variations in electroosmotic peristalsis in tapered microchannel

AbstractThe current study is based on the effects of microrotational dynamics, microinertial effects, and temperature changes on electroosmotic peristalsis in a tapered microchannel. This has been addressed by an analytical study of heat transfer in the setting of electroosmotic peristaltic flow involving a micropolar fluid, specifically considering a symmetrically tapered channel. The Navier–Stokes equation, the Poisson–Boltzmann equation, the energy equation, and the micropolar fluid model are all included in the mathematical model. On the flow and temperature fields, a thorough parametric analysis is carried out, investigating the impacts of numerous variables, including the micropolar parameter, Prandtl number, Brinkman number, Grashof number, thermal conductivity ratio, and channel aspect ratio. The findings show that peristalsis and electroosmosis both contribute to higher heat transfer rates. Notably, the electroosmotic parameter and Brinkman number have a substantial impact on the distribution of temperature. The micropolar parameter and Brinkman number have a significant effect on the flow and temperature fields. Furthermore, electrokinetic phenomena are crucial in controlling the axial and spin velocities of the micropolar fluid. These findings have significant ramifications for the design and optimization of microfluidic devices in engineering and biomedical applications that employ the electroosmotic peristaltic flow of micropolar fluids.

Design and demonstration of an ultra-thin planar microscale capillary pumped loop for electronics thermal management

With new requirements for enhanced thermal management, the minimum size of modern compact electronic devices and the maximum allowable processing speeds of the underlying microprocessor chips have become fundamentally limited by Joule heating. Miniaturizing a conventional loop heat pipe (LHP) or capillary pumped loop (CPL) to enable an ultra-thin high-heat-flux thermal transport system can lead to a paradigm shift in electronics thermal management. However, the complex thermodynamics of a CPL flow loop and the altered behavior of surface tension forces and thermal transport effects at small length scales pose several challenges to the actual implementation of a planar microscale CPL. Here we report on the design aspects of a micro-CPL device fabricated on a 500μm-thick silicon wafer, and experimentally examine the process of evaporation and two-phase flow in the device. An optical study of liquid evaporation in two distinct planar evaporator topologies during device startup reveals the critical roles played by enhanced surface tension forces and increased parasitic heat flows. Critical microfluidic device design aspects that can ensure the successful startup and operation of these ultra-thin thermal management devices are thereby revealed. Device evaporation experiments reveal successful device startup under evaporative heat fluxes of 10–20 W/cm2.

Entropy generation analysis of a micropolar fluid in a corrugated channel with convective and slip conditions

This study focuses on examining the entropy generation in a corrugated channel, considering convective boundary conditions and slip flow, with a micropolar fluid. The governing equations for the micropolar fluid flow, including linear and angular momentum equations, as well as the energy equation, are solved using the perturbation technique. The effects of corrugations, slipping flow, and convective boundary conditions on the entropy generation and the flow behavior are analyzed. The results show that the entropy generation enhanced with the corrugation amplitude, while it reduced for the slip flow. Moreover, entropy generation is affected by the convective boundary conditions, and it is an increasing function with the convective heat transfer coefficient. Additionally, the study demonstrates that micropolar fluid exhibits distinct flow characteristics in comparison to classical Newtonian fluids. These findings have practical implications for the design and optimization of microfluidic devices, as well as for gaining insights into the behavior of micropolar fluids in various engineering applications.

Thermal and mass exchange in a multiphase peristaltic flow with electric-debye-layer effects and chemical reactions using machine learning

The present investigation delves into the analysis of mass and thermal transmission during the peristalsis of a two phase flow of a Prandtl fluid, within a symmetric channel by considering entropy generation and minimization. The considered flow is examined by taking into account the impacts of electroosmotic effects through Electric Debye Layer (EDL) and chemical reactions followed by the lubrication theory approximation. Numerical solutions are acquired for the consequential differential equations through artificial neural networks (ANN) based fitness functions. The artificial neural networks (ANN) based fitness function optimized through hybrid evolutionary algorithms especially ABC (artificial bee colony) and NNA (neural network algorithm) like ANN-ABC-NNA. For the efficiency and validation of the algorithm we conduct the one hundred (100) independent runs. The obtained results through ANN-ABC-NNA are compared with the exact solutions for validation of results. In the present examination, the velocity profile is noticed to increase by the rise in the electroosmotic factor and solid particles concentration, while it decreases for the Prandtl fluid parameter. This research holds practical significance in diverse applications, particularly in the design and optimization of microfluidic devices.

Improving liquid cancer biopsy through computer-aided microfluidic device design based on the tubular pinch effect and Deans flow

A blood test, called a liquid biopsy is being developed by several research groups for the early detection of cancer. The key challenge in this process is enrichment, or isolation, of the small number of cancer cells in blood serum from other cells. This study uses numerical simulations to design devices that advance the state of art in the enrichment of circulating cancer cells. In particular, the lift forces acting on neutrally buoyant small spherical particles in a Poiseuille flow bounded by a wall are modelled using numerical computation. Specifically, we explore the influence of the Reynolds number, distance to the wall, and particle size on these lift forces, building upon previous research on the Segre-Silberberg effect. By validating the mechanism by which particles concentrate at specific positions within the fluid, we confirm the existence of the Segre-Silberberg effect in this system. Subsequently, we apply a customized 3D model of a filtration device to investigate the Segre-Silberberg effect and Deans effect in a non-Poiseuille flow, which can be applied in liquid cancer biopsy. Our results demonstrate that this flow pattern could potentially be used to separate cancer cells from the mean flow. Finally, we apply the flow separation mechanisms in microfluidic design through a rapid 3D design and computational fluid dynamics (CFD) verification cycle. The popular spiral microfluidic design does not demonstrate strong flow separation pattern in our tests, while the sinusoidal design shows much more promise. Further research is needed to empirically evaluate these designs.

Investigation into the optoelectrowetting droplet transport mechanism.

To explore the optoelectronic wetting droplet transport mechanism, a transient numerical model of optoelectrowetting (OEW) under the coupling of flow and electric fields is established. The study investigates the impact of externally applied voltage, dielectric constant of the dielectric layer, and interfacial tension between the two phases on the dynamic behavior of droplets during transport. The proposed model employs an improved Young's equation to calculate the instantaneous voltage and contact angle of the droplet on the dielectric layer. Results indicate that, under the influence of OEW, significant variations in the interface contact angle of droplets occur in bright and dark regions, inducing droplet movement. Moreover, the dynamic behavior of droplet transport is closely associated with various parameters, including externally applied voltage, dielectric layer material, and interfacial tension between the two phases, all of which impact the contact angle and, consequently, the transport process. By summarizing the influence patterns of the three key parameters studied, the optimization of droplet transport performance is achieved. The study employs two-dimensional simulation models to emulate the droplet motion under the influence of the electric field, investigating the OEW droplet transport mechanism. The continuous movement of droplets involves three stages: initial wetting, continuous transport, and reaching a steady position. The findings contribute theoretical support for the efficient design of digital microfluidic devices for OEW droplet movement and the selection of key parameters for droplet manipulation.

Vasculature-on-a-chip technologies as platforms for advanced studies of bacterial infections.

Bacterial infections frequently occur within or near the vascular network as the vascular network connects organ systems and is essential in delivering and removing blood, essential nutrients, and waste products to and from organs. In turn, the vasculature plays a key role in the host immune response to bacterial infections. Technological advancements in microfluidic device design and development have yielded increasingly sophisticated and physiologically relevant models of the vasculature including vasculature-on-a-chip and organ-on-a-chip models. This review aims to highlight advancements in microfluidic device development that have enabled studies of the vascular response to bacteria and bacterial-derived molecules at or near the vascular interface. In the first section of this review, we discuss the use of parallel plate flow chambers and flow cells in studies of bacterial adhesion to the vasculature. We then highlight microfluidic models of the vasculature that have been utilized to study bacteria and bacterial-derived molecules at or near the vascular interface. Next, we review organ-on-a-chip models inclusive of the vasculature and pathogenic bacteria or bacterial-derived molecules that stimulate an inflammatory response within the model system. Finally, we provide recommendations for future research in advancing the understanding of host-bacteria interactions and responses during infections as well as in developing innovative antimicrobials for preventing and treating bacterial infections that capitalize on technological advancements in microfluidic device design and development.

Cilia flow of magnetized Eyring-Powell nanofluid in a vertical thermal channel with viscous dissipation: An application of Adomian decomposition method

In this study, authors explore how magnetic fields and the buoyancy force resulting from temperature differences work together. The study is focusing at how an Eyring-Powell nanofluid behaves in a ciliated channel when both natural convection and magnetic effects are at play. A technique called the symplectic metachoronal wave has been used to analyze this analysis. A physical assumption of small Reynolds number is considered to simplify the equations describing the flow rate of the Eyring-Powell nanofluid, making it easier to understand. To get a closed form solution, we have incorporated Adomian decomposition method (ADM). It has been observed that the flow is sped up by 10% with increase in the Eyring-Powell fluid parameter M. The quantity of heat transfer increases with increasing values of the Hartmann, Eyring-Powell fluid parameters, and Brinkmann numbers. This study has implications for bio-inspired engineering, medical applications, and the design of microfluidic devices.

Raman and Surface-Enhanced Raman Scattering Detection in Flowing Solutions for Complex Mixture Analysis.

Raman scattering provides a chemical-specific and label-free method for identifying and quantifying molecules in flowing solutions. This review provides a comprehensive examination of the application of Raman spectroscopy and surface-enhanced Raman scattering (SERS) to flowing liquid samples. We summarize developments in online and at-line detection using Raman and SERS analysis, including the design of microfluidic devices, the development of unique SERS substrates, novel sampling interfaces, and coupling these approaches to fluid-based chemical separations (e.g., chromatography and electrophoresis). The article highlights the challenges and limitations associated with these techniques and provides examples of their applications in a variety of fields, including chemistry, biology, and environmental science. Overall, this review demonstrates the utility of Raman and SERS for analysis of complex mixtures and highlights the potential for further development and optimization of these techniques. Expected final online publication date for the Annual Review of Analytical Chemistry, Volume 17 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Single Step Isolation of Extracellular Vesicles from Large-Volume Samples with a Bifurcated A4F Microfluidic Device.

Extracellular vesicles (EVs) hold immense potential for various biomedical applications, including diagnostics, drug delivery, and regenerative medicine. Nevertheless, the current methodologies for isolating EVs present significant challenges, such as complexity, time consumption, and the need for bulky equipment, which hinders their clinical translation. To address these limitations, we aimed to develop an innovative microfluidic system based on cyclic olefin copolymer-off-stoichiometry thiol-ene (COC-OSTE) for the efficient isolation of EVs from large-volume samples in a continuous manner. By utilizing size and buoyancy-based separation, the technology used in this study achieved a significantly narrower size distribution compared to existing approaches from urine and cell media samples, enabling the targeting of specific EV size fractions in future applications. Our innovative COC-OSTE microfluidic device design, utilizing bifurcated asymmetric flow field-flow fractionation technology, offers a straightforward and continuous EV isolation approach for large-volume samples. Furthermore, the potential for mass manufacturing of this microfluidic device offers scalability and consistency, making it feasible to integrate EV isolation into routine clinical diagnostics and industrial processes, where high consistency and throughput are essential requirements.

Blasius–Rayleigh–Stokes nanofluid dusty flow influenced by Cattaneo–Christov double diffusion and melting heat transfer — application of response surface methodology

This paper focuses on the study of Blasius–Rayleigh–Stokes nanofluid dusty flow with generalized Fourier and Fick laws under the influence of a transitive magnetic field. The Blasius–Rayleigh–Stokes nanofluid dusty flow has significant applications in various fields, including the design of heat exchangers, microfluidic devices and industrial processes involving the transportation of suspended particles in fluids. This paper considers the impact of melting heat transfer at the surface boundary. By employing relevant transformations, the mathematical model is transformed into a system of self-similar equations. The solution to this set of highly nonlinear equations is obtained using the bvp4c numerical method in combination with the response surface methodology (RSM) statistical approach. The results are presented through graphical illustrations and numerically calculated tabulated values. It is observed that the fitted model for the skin friction coefficient [Formula: see text] optimal. Moreover, the model parameters [Formula: see text], Q, [Formula: see text], M and L are linearly and quadratically significant in explaining the variation presented for skin friction coefficient [Formula: see text]. This indicates the response skin friction coefficient [Formula: see text] is minimized to 0.005 at [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] and is maximized to 1.387 at [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text].

Accelerated Computational Fluid Dynamics Simulations of Microfluidic Devices by Exploiting Higher Levels of Abstraction.

The design of microfluidic devices is a cumbersome and tedious process that can be significantly improved by simulation. Methods based on Computational Fluid Dynamics (CFD) are considered state-of-the-art, but require extensive compute time-oftentimes limiting the size of microfluidic devices that can be simulated. Simulation methods that abstract the underlying physics on a higher level generally provide results instantly, but the fidelity of these methods is usually worse. In this work, a simulation method that accelerates CFD simulations by exploiting simulation methods on higher levels of abstraction is proposed. Case studies confirm that the proposed method accelerates CFD simulations by multiple factors (often several orders of magnitude) while maintaining the fidelity of CFD simulations.

Order–disorder transitions within deformable particle suspensions in planar Poiseuille flow

Three-dimensional simulations of the ordering of elastic capsule suspensions within planar Poiseuille flow channels are reported. The simulations utilize the immersed boundary method coupled with the lattice Boltzmann method to capture the complex flow-induced capsule deformations and hydrodynamic interactions within the suspensions. A parametric study is presented whereby the confinement ratio and the particle deformability are varied independently within a two-dimensional range relevant to this ordering phenomenon. The initial distribution of capsules is random, and the simulations evolve the system from a disordered state to an ordered one, while an order parameter that quantifies the fraction of capsules belonging to one-dimensional train assemblies is computed throughout time. A monotonic increase in ordering is observed with increasing deformability. However, an optimal confinement ratio is identified corresponding to a peak in the order parameter. This peak is attributed to the competition between increasing long-range capsule attractions and decreasing in-plane capsule density (with fixed volume fraction) as the confinement ratio increases. Simulations are also performed to understand how dispersity in capsule size and deformability impact the degree of ordering. It is shown that ordering is quite sensitive to dispersity in capsule size, and much less sensitive to dispersity in deformability. Overall, the results provide important insights for the design of microfluidic devices.

Sheathless inertial particle focusing methods within microfluidic devices: a review.

The ability to manipulate and focus particles within microscale fluidic environments is crucial to advancing biological, chemical, and medical research. Precise and high-throughput particle focusing is an essential prerequisite for various applications, including cell counting, biomolecular detection, sample sorting, and enhancement of biosensor functionalities. Active and sheath-assisted focusing techniques offer accuracy but necessitate the introduction of external energy fields or additional sheath flows. In contrast, passive focusing methods exploit the inherent fluid dynamics in achieving high-throughput focusing without external actuation. This review analyzes the latest developments in strategies of sheathless inertial focusing, emphasizing inertial and elasto-inertial microfluidic focusing techniques from the channel structure classifications. These methodologies will serve as pivotal benchmarks for the broader application of microfluidic focusing technologies in biological sample manipulation. Then, prospects for future development are also predicted. This paper will assist in the understanding of the design of microfluidic particle focusing devices.

A review on the surface modification of materials for 3D-printed diagnostic devices.

Three-dimensional (3D) printing in tissue engineering and biosensing of analytes by using biocompatible materials or modifying surface structures is an upcoming area of study. This review discusses three common surface modification techniques, viz. alkaline hydrolysis, UV light photografting, and plasma treatment. Alkaline hydrolysis involves the reaction of an alkaline solution with the surface of a material, causing the surface to develop carboxyl and hydroxyl groups. This technique can enhance the biocompatibility, surface wettability, adhesion, printability, and dyeability of materials, such as acrylonitrile butadiene styrene (ABS), polycarbonate, and polylactic acid (PLA). This review also mentions details about some of the surface-modified 3D-printed diagnostic devices. Although most of the devices are modified using chemical processes, there are always multiple techniques involved while designing a diagnostic device. We have, therefore, mentioned some of the devices based on the materials used instead of categorising them as per modification techniques. 3D printing helps in the design of sophisticated shapes and structures using multiple materials. They can, therefore be used even in the design of microfluidic devices that are very useful for biosensing. We have also mentioned a few materials for printing microfluidic devices.

Isolation of acute myeloid leukemia blasts from blood using a microfluidic device.

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults and associated with poor prognosis. Unfortunately, most of the patients that achieve clinical complete remission after the treatment will ultimately relapse due to the persistence of minimal residual disease (MRD), that is not measurable using conventional technologies in the clinic. Microfluidics is a potential tool to improve the diagnosis by providing early detection of MRD. Herein, different designs of microfluidic devices were developed to promote lateral and vertical mixing of cells in microchannels to increase the contact area of the cells of interest with the inner surface of the device. Possible interactions between the cells and the surface were studied using fluid simulations. For the isolation of leukemic blasts, a positive selection strategy was used, targeting the cells of interest using a panel of specific biomarkers expressed in immature and aberrant blasts. Finally, once the optimisation was complete, the best conditions were used to process patient samples for downstream analysis and benchmarking, including phenotypic and genetic characterisation. The potential of these microfluidic devices to isolate and detect AML blasts may be exploited for the monitoring of AML patients at different stages of the disease.

A computational study of cell membrane damage and intracellular delivery in a cross-slot microchannel.

We propose a three-dimensional computational framework to simulate the flow-induced cell membrane damage and the resulting enhanced intracellular mass transport in a cross-slot microchannel. We model the cell as a liquid droplet enclosed by a viscoelastic membrane and solve the cell deformation using a well-tested immersed-boundary lattice-Boltzmann method. The cell membrane damage, which is directly related to the membrane permeability, is considered using continuum damage mechanics. The transport of the diffusive solute into the cell is solved by a lattice-Boltzmann model. After validating the computational framework against several benchmark cases, we consider a cell flowing through a cross-slot microchannel, focusing on the effects of the flow strength, channel fluid viscosity and cell membrane viscosity on the membrane damage and enhanced intracellular transport. Interestingly, we find that under a comparable pressure drop across the device, for cells with low membrane viscosity, the inertial flow regime, which can be achieved by driving a low-viscosity liquid at a high speed, often leads to much larger membrane damage, compared with the high-viscosity low-speed viscous flow regime. However, the enhancement can be significantly reduced or even reversed by an increase of the cell membrane viscosity, which limits cell deformation, particularly in the inertial flow regime. Our computational framework and simulation results may guide the design and optimisation of microfluidic devices, which use cross-slot geometry to disrupt cell membranes to enhance intracellular delivery of solutes.

A novel ratiometric design of microfluidic paper-based analytical device for the simultaneous detection of Cu2+ and Fe3+ in drinking water using a fluorescent MOF@tetracycline nanocomposite.

The regular and on-site monitoring of ions in drinking water is essential for safeguarding public health, ensuring high water quality, and preserving the ecological balance of aquatic ecosystems. Thus, developing a portable analytical device for the rapid, cost-effective, and visual on-site detection of multiple environmental pollutants is notably significant. In the present work, a novel ratiometric microfluidic paper-based analytical device (μPAD) was designed and developed for the simultaneous detection of Fe3+ and Cu2+ ions in water samples taking advantages from built-in masking zone. The μPAD was functionalized with a greenish-yellow fluorescent Zn-based metal-organic framework@tetracycline (FMOF-5@TC) nanocomposite, and the ratiometric design was based on the change in emission color from greenish yellow (FMOF-5@TC) to blue (FMOF-5). The μPAD consisted of one sample zone linked to two detection zones via two channels: the first channel was for the detection of both ions, while the second was intended for detecting only Cu2+ ions and comprised a built-in masking zone to remove Fe3+ ions prior to reaching the detection zone. The corresponding color changes were recorded with the aid of a smartphone and RGB calculations. The linear ranges were 0.1-80 μM for Cu2+ and 0.2-160 μM for Fe3+, with limits of detection of 0.027 and 0.019 μM, respectively. The simple μPAD design enabled the simultaneous detection of Cu2+ and Fe3+ ions in drinking water samples with excellent accuracy and precision, with spike recoveries of 81.28-96.36% and 83.01-102.33% for Cu2+ and Fe3+, respectively.

Effective colloidal emulsion droplet regulation in flow-focusing glass capillary microfluidic device via collection tube variation.

Colloidal emulsion droplets, created using glass capillary microfluidic devices, have been found in a myriad of applications, serving as subtle microcarriers, delicate templates, etc. To meet the objective requirements under varying circumstances, it is crucial to efficiently control the morphology and dimensions of the droplets on demand. The glass capillary collection tube is a crucial component of the flow-focusing microfluidic system due to its close association with the geometrical confinement of the multiphasic flow. However, there are currently no guidelines for the design of the morphology and dimensions of the glass capillary collection tube, which shall result in a delay in assessing serviceability until after the microfluidic device is prepared, thereby causing a loss of time and effort. Herein, an experimental study was conducted to investigate the effect of the geometrical characteristics of glass capillary collection tubes on the production of colloidal emulsion droplets. After characterizing the generated colloidal emulsion droplets, it was found that the geometrical variations of the glass capillary collection tube resulted in numerical disparities of droplets due to different degrees of flow-focusing effects. The stronger flow-focusing effect produced smaller droplets at a higher frequency, and the dimensional variation of colloidal emulsion droplets was more responsive to varying flow rates. Furthermore, the transformation from colloidal single-core double-emulsion droplets to multi-core double-emulsion droplets also changed with the flow rate due to the glass capillary collection tube morphology-determined varying flow-focusing effect. These experimental findings can offer qualitative guidance for the design of glass capillary microfluidic devices in the preliminary stage, thus facilitating the smooth production of desired colloidal emulsion droplets.