Microfluidics and Nanofluidics最新文献

In the context of mature oil fields, the management of water production stands out as a formidable challenge. Our prior research endeavors (Saikia et al. J Pet Sci Eng 2020, ACS Omega 2021) have introduced an innovative Pickering emulsified gel system tailored for the precise adjustment of relative permeability in high-temperature reservoirs. To make this system work better, it is required to fully understand how it controls water flow. Traditionally, conformance control studies rely on data from core flooding tests, CT scans, and nuclear magnetic resonance (NMR) techniques, among other methods. However, these traditional approaches often struggle to provide real-time visual data, which limits their accuracy in predicting how conformance mechanisms actually work. In our research study, using two distinct glass micromodels (Micromodel I-water-wet and Micromodel II-oil-wet), we conducted Pickering emulsified gel treatments at 105 °C. Microfluidic analysis revealed that the emulsion enters the pore space as slugs, coalescing during injection. The subsequent gelation of the aqueous phase restricts water flow, while oil preferentially flows through specific channels created by the separated oleic phase. These findings challenge the previously proposed Thin Film mechanism, suggesting instead a Relative Permeability Modified Channel Flow. This research provides a deeper understanding of the Pickering emulsified gel system’s conformance control mechanism, highlighting its potential for managing water production in high-temperature reservoirs.

We employ a three-dimensional numerical model to analyze the dynamics of single-phase flow in a parallel branched microchannel with varying geometric dimensions of constrictions. The primary objective is to delve into the intricacies of flow within microdevices featuring a branched network and constrictions. The findings illustrate nonlinear variations in velocity, pressure, acceleration, and shear stress along the streamwise direction, underscoring their significant dependence on the converging/diverging angles of the constrictions. To gain deeper insights into the effects of geometric parameters resulting from converging/diverging constrictions in microchannels, a geometric Reynolds number is introduced as the governing parameter for flow transition, further highlighting the novel approach. Our results demonstrate a notable improvement in the magnitude of inertial forces, a feature uncommon in simple microchannels. From the results, it is asserted that microdevices with higher converging–diverging angles combined with lower width ratios are a preferable choice compared to those with lower converging–diverging angles and higher width ratios. Such configurations exhibit lower pumping power, contributing to enhanced energy efficiency. These findings provide fundamental insights that can guide the design of necessary modifications aimed at improving the performance of micropumps or microvalves.

Microfluidic-MEMS (micro-electromechanical system) devices consist of complex subsystems in which the transfer of mass, momentum and energy is critical. This is often achieved by a pressure gradient-driven, low-speed rarefied gas transport in long micro-ducts. Gaseous rarefaction, and geometrical properties of micro-ducts, such as cross-section profile and surface roughness, play a decisive role in the segregation of the flow into inertia-driven and surface-dominated domains. In this work, a parallel stochastic kinetic particle solver that solves the low-variance Boltzmann Bhatnagar-Gross-Krook (BGK) formulation is utilized to study isothermal rarefied gas transport through polar and triangular cross-sections. The effect of geometrical features such as surface proximity to the inertial core and the role of corners, are characterized. A novel parameter to indicate surface influence is introduced, which can be gainfully used in MEMS design and optimization.

Microfluidics has emerged as a highly promising technology for miniaturizing chemical analysis laboratory into a single, small lab-on-a-chip device. In our previous research, we have developed an innovative approach to particle-based microfluidics by screen printing silica gel microparticles onto glass substrate to create a patterned porous material. In this article we demonstrate a multi-step sample analysis – combining conventional and affinity thin-layer chromatography with competitive assay for detection – along with blister reservoirs that can be integrated into the particle-based microfluidic point-of-care test. This integration achieves high analytical performance and makes the test simple to use. Biotin was chosen as the exemplary analyte, because measuring it is crucial in immunoassays, where high circulating biotin concentrations can lead to false results. This research also addresses the challenge of biotin interference in immunoassays by making it possible to produce rapid biotin tests. Need for these tests is particularly critical in emergency situations. Validation of the developed test demonstrated a dynamic range of 0.09 to 0.24 µg ml^− 1 and that artificial urine matrix does not have significant effect on the results. This would make it possible to assess whether the biotin interference occurs in urine sample immunoassays.

The utilization of external magnetic or electric fields, particularly through a Riga setup, markedly enhances flow dynamics by mitigating frictional forces and turbulent fluctuations, thereby facilitating superior flow management. Such improvements are especially beneficial in optimizing the operational efficiency of machinery and turbines. Our research focuses on the behavior of a weakly ionized fluid within a porous, infinitely extended Riga channel (or electromagnetic channel) set in a rotational framework affected by Hall and ion-slip electric fields. This model integrates the cumulative repulsions of an abruptly applied pressure gradient, electromagnetic forces, electromagnetic radiation, and chemical reactions. The physical configuration of the model features a stationary right wall and a left wall subjected to transverse vibrations, establishing a complex flow environment. This scenario is analytically modeled using time-dependent partial differential equations, with the Laplace transform (LT) method applied to achieve a closed-form solution for the flow controlling equations. Through detailed graphical and tabular data, the study explores the impact of various pivotal parameters on the model’s flow traits and quantities. Our results indicate that an upswing in the modified Hartmann number significantly enhances fluid flow within the channel, with the primary flow component showing marked improvement as Hall and ion-slip parameters amplify, and secondary flow component diminishing. Additionally, species concentration lowers with higher Schmidt numbers and chemical reaction rates, while an expanded modified Hartmann number correlate with enhanced shear stresses at the channel wall. Moreover, an elevation in the radiation parameter reduces the rate of heat transfer (RHT) at the vibrating wall, whereas RHT at the stationary wall improves. This study has profound implications across several fields, notably in fusion energy research, spacecraft propulsion systems, satellite operations, aerospace engineering, and advanced manufacturing technologies.

In the tumor microenvironment (TME), the interaction between cancer cells and the microvascular network plays a crucial role in cancer progression. It is also well known that an extremely low oxygen concentration is generated in the TME. However, the effects of oxygen concentration on the interaction between cancer cells and the microvascular network remain poorly understood. In the present study, we developed a microfluidic device with three gel channels and used this device to co-culture cancer cells and a microvascular network. We then investigated the cellular dynamics at different oxygen concentrations. Cancer cells and cells forming a microvascular network (endothelial cells and fibroblasts) were separately mixed with fibrin gels and placed in separate gel channels that flanked a middle gel channel lacking cells. During a seven-day co-culture, the dynamics of cancer cells and formation of a three-dimensional microvascular structure were observed. Cell culture was conducted at three different oxygen concentrations: atmospheric oxygen (21% O₂), physiological normoxia (5% O₂), and physiological hypoxia (1% O₂, resembling the TME). Inspection revealed that cancer cells migrated toward the microvascular network under the co-culture conditions, a property that was potentiated at lower oxygen levels. Under physiological normoxia, endothelial cells formed a thick, dense microvascular network rather than migrating towards the cancer cells. In contrast, under physiological hypoxia, endothelial cells did not exhibit angiogenesis toward cancer cells. These results suggest that the microfluidic device described here will be useful for investigating the interactions between cancer cells and microvascular network under various oxygen conditions.

The flow analysis of electrolyte solution in microchannel/capillary is essential in various applications of health care such as dialysis and diagnosis processes of biological fluids/samples. To investigate the flow analysis in a homogeneous and isotropic porous microchannel with two membranes fitted at the upper wall surface, a novel biophysical model is presented mathematically. The lower wall surface is kept stationary and negatively charged to analyse the influence of the electroosmosis mechanism. The membranes have a self-propagating pumping process with varying amplitude and phase lag. The continuity and momentum equations are considered to describe the fluid flow and the Poisson–Boltzmann equation is taken to analyse the distribution of the electric potential for the electrolyte solution in the normal direction to a charged surface. To derive the governing equations, we have considered the approximation of low Reynolds number and Debye-Hückel linearization. Using MATLAB coding, key results like velocity, pressure difference, skin friction, volumetric flow rate, and stream function are computed under the influence of significant parameters. Present study finds that the movement of the electrolyte solution can be driven by membrane-based pumping at a small scale and further regulated by electroosmosis. The resistance due to the porous medium impacts the velocity and volumetric flow rate but this resistance can be mitigated by increasing the strength of the external electric field. This analysis is potentially useful for developing membrane-based microfluidic devices to analyse the biological flow at the micro-scale.

In recent years, single cell isolation and analysis have become crucial, driven by the need to study rare cells in cell biology research, diagnostics, and personalized medicine. However, existing platforms for isolating small cell numbers are expensive, labor-intensive, and not widely accessible. To address this, we present a low-cost, repeatable microfluidic platform capable of retrieving 1-100 cells with high accuracy and minimal sample loss. The system utilizes a 2D hydrodynamic focusing chip and a pipette tip as a cell reservoir, enhanced by a flexible hydraulic reservoir (FHR) to prevent sample loss. Cells are collected using a syringe pump-driven flow, monitored in real-time under a microscope, and counted using image processing software. To validate the platform, MCF7 breast cancer cells were passed through the microchannel, with target retrieval numbers ranging from 1 to 100 cells. The average retrieved cell count was found to be 1.0 ± 0.0, 9.2 ± 2.4, 46.0 ± 5.9 and 98.5 ± 6.2 for 1, 10, 50, and 100 targeted number of cells, respectively. The counting accuracy of the code was demonstrated by the average deviation between the code count and retrieved number of cells being 0 ± 0.6, -0.3 ± 1.7, -1.6 ± 0.9, and 3.9 ± 4.8, respectively for 1, 10, 50, and 100 targeted cells. The process took less than 10 min, with cell counts matching targets closely and demonstrating high accuracy. Importantly, cell viability remained unaffected post-process. This method offers a cost-effective, robust solution for precise cell counting and retrieval, suitable for various downstream applications.

Standing surface acoustic waves (sSAW) emerged as a flexible tool for precise manipulation of spherical and non-spherical objects in Lab-on-a-Chip devices. While the manipulation of suspended particles and cells in acoustofluidic devices is mostly dominated by acoustic forces due to acoustic scattering and the acoustically induced fluid flow, surface acoustic waves are inherently linked to an inhomogeneous electric field. The superimposed effects of dielectrophoretic forces and torques on polarizable particles are less explored in microfluidics using sSAW. In this study, a thorough analysis of the physical interplay of acoustophoresis and dielectrophoresis aims to bridge this gap. In comprehensive experiments, the dielectrophoretic impact on the behavior of spherical and non-spherical particles is distinguished by screening the electric field of the sSAW inside the micro channel locally. As a result, particles are forced into trapping locations across the entire channel height. However, the height position close to the bottom differs between the screened and non-screened region. Regardless of the shape of the particles used in this study, particles are forced towards the bottom at the region with screening, while being levitated at regions without screening. This indicates clearly the influence of the electric field in close vicinity to the substrate surface. Furthermore, the unintuitive preferred orientation of prolate spheroids perpendicular to the pressure nodes of the sSAW recently reported, is confirmed in both region regardless of the presence of the electric field. Based on a three-dimensional numerical model, this orientation results not only due to the acoustic torque but is also caused by the dielectrophoretic torque, which complement each other. The experimental and numerical findings are in excellent agreement and provide deep insights into the underlying physical mechanisms responsible for patterning and orientation of the particles.

Electrocoalescence is a valuable phenomenon for merging droplets and is widely used in various applications such as the demulsification of crude oil, chemical or biological reaction using a small volume and so on. The ‘non-coalescence’ or ‘partial coalescence’ regimes, at which the droplet pair does not completely merge, appear under particular conditions, and researchers figured out these conditions using an equal-sized droplet pair. However, actual applications involve the merging of an unequal-sized droplet pair; the conditions for the non-coalescence or partial coalescence of unequal-sized droplet pair have not been clearly established. In this study, we evaluated the electrocoalescence behavior of a droplet pair with varying the droplet radius ratio, the initial distance between droplets, and the strength of electric fields, and found the conditions when non-coalescence and partial coalescence occur for unequal- and equal-sized droplet pairs. We discovered that unequal-sized droplet pair demonstrates non-coalescence and partial coalescence more frequently than equal-sized pair. Additionally, non-coalescence and partial coalescence occurred for lower strength of electric field as droplet size ratio and initial distance between droplets increased. Finally, we demonstrate that the unequal formation of the cone angle for unequal-sized droplet pair causes different electrocoalescence behaviors compared with equal-sized droplet pair. We anticipate that this study will contribute to the identification of an appropriate electric field range for diverse electrocoalescence applications.