Microfluidics and Nanofluidics最新文献

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.

Nitrocellulose microspheres have garnered extensive use in propellants and launching agents due to their inherent safety, robust flowability, and high explosive power. However, conventional preparation methods for these microspheres are often hampered by complex processes, low safety factor and poor sphericity. This study explores an innovative approach to nitrocellulose microsphere fabrication utilizing microfluidic technology. We designed and assembled two high-throughput preparation devices—a coaxial and a centrifugal device—employing 3D printing technology. Our findings demonstrate an 18-fold increase in efficiency over traditional single-pass microfluidic techniques. Additionally, we examined the impact of these devices on the microspheres’ size distribution. The proposed device showcases significant advantages, including reduced cost, enhanced efficiency, and shorter production cycles, indicating promising potential for wide-scale application in nitrocellulose microsphere preparation.

The performance of hollow fiber membrane contactor for CO₂ removal using MEA-based nanofluid was experimentally evaluated. Different types of nanoparticles, including Al₂O₃, Fe₃O₄, and functionalized MWCNT in this study. The influence of various operating conditions including gas and absorbent flow rates, absorbent concentration, and nanofluid characteristics on separation performance was thoroughly examined. The results showed that compared to conventional amine solvents, the nanofluid absorbents significantly enhance CO₂ absorption performance. In comparison to the base fluid, the mass transfer coefficient was raised by 320, 120, and 40% for 0.15 wt% MWCNT, Al₂O₃ and Fe₂O₃, respectively. The MWCNT showed much more compliance with amine solvents due to its carboxyl functional groups and higher surface area which make it more stable in a strong polar mixture. The study underscores the importance of stability, viscosity, and shear stress of nanofluids as key parameters affecting CO₂ absorption performance.

In the present study, we explore the dynamics of bubble formation in a flow-focusing device designed for gas-non-Newtonian liquid two-phase flow. The flow-focusing device with a cross-section of a square (300 μm × 300 μm) is constructed on polydimethylsiloxane using lithographic techniques and subsequently sealed with polymethylmethacrylate. A high-speed camera is employed to document the process of bubble formation during the experiment, complemented by computational fluid dynamics methods for an in-depth analysis. The gas is nitrogen, and the liquid is sodium carboxymethyl cellulose solutions with mass fractions of 0.1, 0.2, and 0.3%, respectively. The inlet flow rates of gas and liquid are set at 1–2 ml/min in the simulation and the experiment, and the observed flow patterns are all slug flows. Experimental findings suggest that the duration of bubble formation can be bifurcated into two distinct parts. The first part is predominantly influenced by the velocity of the inlet gas, and the correlation coefficient between velocity and time is −0.56, while the second part is impacted by the shear-thinning properties of the liquid, which are correlated with the flow index and viscosity coefficient of the non-Newtonian liquids, and the correlation coefficients are −0.47 and 0.48, respectively. The computational fluid dynamics results of gas-non-Newtonian liquid two-phase flow with gas and liquid flow rates of 2 ml/min corroborate that the manifestation of the aforementioned time segmentation phenomenon primarily depends on the vortex intensity at the bubble’s head and the orientation of pressure gradients. When the bubble neck size approaches 0, the viscosity of the surrounding liquid decreases rapidly, and alterations in the velocity field near the bubble neck trigger fluctuations in the viscosity of the non-Newtonian liquid, thereby influencing the bubble formation process.

The Molecular Tagging (MT) technique is a promising methodology for locally measuring velocity and temperature fields in rarefied gas flows. Recently, Molecular Tagging Velocimetry (MTV) has been successfully applied to gas flows in mini-channels in the continuum regime at high pressure and early slip-flow regime at lower pressure. As the operating pressure decreases, diffusion effects become more pronounced, and in MTV, they hinder the extraction of the correct velocity profile by simply dividing the displacement profile of the tagged molecular line by time of flight. To address this issue, a reconstruction method that considers Taylor dispersion was previously developed to extract the velocity profile, considering the diffusion effects of the tracer molecules within the carrier gas. This reconstruction method successfully extracted the correct velocity profile in the continuum flow regime. However, the method still faces challenges in the slip-flow regime. Since there is currently no consensus in the literature regarding the kinetic diameter value of acetone vapor, the diffusion coefficient estimation is uncertain especially at low pressures. This is why, in this study, we propose an original optical method to measure the diffusion coefficient of acetone vapor. This is achieved by linking the temporal evolution of the spatial photoluminescence distribution of acetone vapor to the diffusion coefficient via the Chapman-Enskog theory. Our research provides measurements of these parameters for a wide range of pressures (0.5–10 kPa) at ambient temperature.

The formation of double-emulsions or core/shell microdroplets in microchannels, essential for various chemical applications, traditionally relies on costly and time-consuming laboratory methods. In this regard, computational fluid dynamics (CFD) and artificial neural network (ANN) techniques were employed. The present study developed ANN models to predict the relationship between shell thickness and double-emulsion size in a double-T microchannel, using two datasets comprising 180 experimental and CFD data points. Assessing this relationship involved analyzing various input factors, including the Capillary, Weber (case A), and Reynolds numbers (case B) of the core, shell, and continuous phases. Among twelve training algorithms and four activation functions, the Levenberg–Marquardt (LM) algorithm with sigmoidal activation functions (Tansig and Logsig), in contrast to the linear activation functions (Poslin and Purelin), achieved the highest predictive accuracy. Additionally, the predictive accuracy of ANN models was found to be significantly improved when trained using a combination of capillary and Weber numbers, as opposed to models trained only using capillary, Weber, and Reynolds numbers. The optimal neural network architectures were [10 5] neurons for case A (tansig and logsig) and [8] neurons for case B (tansig), yielding coefficients of determination (R²) of 0.99 and 0.98, respectively. These models demonstrated high precision and effective generalization, evidenced by statistical measures such as R², MSE, RMSE, AAD, %AARD, and computational time. Moreover, their ability to generalize within the training dataset further substantiates their predictive capacity.