Microfluidics and Nanofluidics最新文献

Understanding the slip behaviors on the graphene surfaces is crucial in the field of nanofluidics and nanofluids. The reported values of the slip length in the literature from both experimental measurements and simulations are quite scattered. The presence of low concentrations of functional groups may have a greater impact on the flow behavior than expected. Using non-equilibrium molecular dynamics simulations, we specifically investigated the influence of hydroxyl-functionalized graphene surfaces on the boundary slip, particularly the effects related to hydrogen bond dynamics. We observed that hydroxyl groups significantly hindered the sliding motion of neighboring water molecules. Hydrogen bonds can be found between hydroxyl groups and water molecules. During the flow process, these hydrogen bonds continuously form and break, resulting in the energy dissipation. We analyzed the energy balance under different driving forces and proposed a theoretical model to describe the slip length which also considers the influence of hydrogen bond dynamics. The effects of the driving force and the surface functional group concentration were also studied.

Kinetic theory and modeling have been proven extremely suitable in computing the flow rates in rarefied gas pipe flows, but they are computationally expensive and more importantly not practical in design and optimization of micro- and vacuum systems. In an effort to reduce the computational cost and improve accessibility when dealing with such systems, two efficient methods are employed by leveraging machine learning (ML). More specifically, random forest regression (RFR) and symbolic regression (SR) have been adopted, suggesting a framework capable of extracting numerical predictions and analytical equations, respectively, exclusively derived from data. The database of the reduced flow rates W used in the current ML framework has been obtained using kinetic modeling and it refers to nonlinear flows through circular tubes (tube length over radius (l in [0,5]) and downstream over upstream pressure (p in [0,0.9])) in a very wide range of the gas rarefaction parameter (delta in [0,10^3]). The accuracy of both RFR and SR models is assessed using statistical metrics, as well as the relative error between the ML predictions and the kinetic database. The predictions obtained by RFR show very good fit on the simulation data, having a maximum absolute relative error of less than (12.5%). Various expressions of the form of (W=W(p,l,delta )) with different accuracy and complexity are acquired from SR. The proposed equation, valid in the whole range of the relevant parameters, exhibits a maximum absolute relative error less than (17%). To further improve the accuracy, the dataset is divided into three subsets in terms of (delta) and one SR-based closed-form expression of each subset is proposed, achieving a maximum absolute relative error smaller than (9%). Very good performance of all proposed equations is observed, as indicated by the obtained accuracy measures. Overall, the present ML-predicted data may be very useful in gaseous microfluidics and vacuum technology for engineering purposes.

With continuous efforts of researchers all over the world, the field of inertial microfluidics is constantly growing, to cater to the requirements of diverse areas like healthcare, biological and chemical analysis, materials synthesis, etc. The scale, automation, or unique physics of these systems has been expanding their scope of applications. In this review article, we have provided insights into the fundamental mechanisms of inertial microfluidics, the forces involved, the interactions and effects of different applied forces on the suspended particles, the underlying physics of these systems, and the description of numerical studies, which are the prime factors that govern designing of effective and practical devices.. Further, we describe how various forces lead to the migration and focusing of suspended particles at equilibrium positions in channels with different cross-sections and also review various factors affecting the same. We also focus on the effect of suspended particles on the flow of fluids within these systems. Furthermore, we discuss how Dean flows are created in a curved channel and how different structures affect the creation of secondary flows, and their application to mixing, manipulating, and focusing particles as fluid. Finally, we describe various applications of microfluidics for diagnostic and other clinical purposes, and discuss the challenges and advancements in this field. We anticipate that this manuscript will elucidate the basics and quantitative aspects of inertial fluid dynamic effects for application in biomedicines, materials synthesis, chemical process control, and beyond.

Graphical abstract

Active sorting of particle in the dielectrophoresis microfluidic channel by applying the boundary element method and point-particle approach is investigated. In this paper, we investigate the dynamics of particle sorting for various particle sizes, electrode potential, electrode spacing, and relative permittivity. The microfluidic device consists a straight mother channel, two inlets, two outlets, and up and down triangular electrodes. The boundary element method is applied to numerically solve the integral equations of the Laplace differential equation of electric potential and Stokes differential equation. In continue, the dynamics of particle separation using the point-particle approach is investigated. Numerical results indicate that there are three different particle sorting regimes. They are called by up-outlet, down-outlet, and trapped regimes. The results illustrate that there are a good agreement between two numerical approaches.

In this work, we have reported continuous flow synthesis of 1-ethyl-3-methylimidazolium ethyl sulfate ionic liquid in a PTFE micro-capillary. A Y-shaped microfluidic junction is used to mix the incoming reactants. Effects of independent parameters like velocity, reaction temperature, and micro-capillary diameter on product yield, rate of production, and space–time yield are reported. Yield is seen to increase monotonically as reaction temperature is increased, while it reduces with an increase in diameter of the micro-capillary. A maxima in yield is observed as flow velocity is increased. A space–time yield of 1258.4 g/min.L is obtained at a reaction temperature of 80 ⁰C using a 300 µm micro-capillary. A two-dimensional computational fluid dynamics (CFD) model of the reacting system has been developed to confirm and explain the observed experimental trends. The simulations were able to qualitatively predict the experimental trends. The simulations also investigated the effect of shapes of different obstacles placed in the flow path.

The active manipulation of particle and cell trajectories in fluids by high-frequency standing surface acoustic waves (sSAW) allows to separate particles and cells systematically depending on their size and acoustic contrast. However, process technologies and biomedical applications usually operate with non-spherical particles, for which the prediction of acoustic forces is highly challenging and remains a subject of ongoing research. In this study, the dynamical behavior of prolate spheroids exposed to a three-dimensional acoustic field with multiple pressure nodes along the channel width is examined. Optical measurements reveal an alignment of the particles orthogonal to the pressure nodes of the sSAW, which has not been reported in literature so far. The dynamical behavior of the particles is analyzed under controlled initial conditions for various motion patterns by imposing a phase shift on the sSAW. To gain detailed understanding of the particle dynamics, a three-dimensional numerical model is developed to predict the acoustic force and torque acting on a prolate spheroid. Considering the acoustically induced streaming around the particle, the numerical results are in excellent agreement with experimental findings. Using the proposed numerical model, a dependence of the acoustic force on the particle shape is found in relation to the acoustic impedance of the channel ceiling. Hence, the numerical model presented herein promises high progress for the design of separation devices utilizing sSAW, exploiting an additional separation criterion based on the particle shape.

We investigate analytically and experimentally the flow rate through a biochip in a circuit involving a peristaltic pump and reservoirs with liquid/air interfaces. Peristaltic pumps are a convenient way to achieve recirculation in microfluidic circuits. We consider different cases: reservoirs in contact with ambient air, tight reservoirs, and imperfect tightness leading to air or liquid leaks. We demonstrate that if changes in hydraulic resistance are slow enough, i.e., if cells do not proliferate too fast, the system may reach an equilibrium, with a difference in liquid height between inlet and outlet reservoir compensating the pressure drop in the biochip. We compute the flow rate through the biochip in the transient regime as well as the characteristic time. We also show that depending on the circuit dimensions, this equilibrium may never be reached. We provide guidelines to design tubings and reservoirs to avoid this situation and ensure a smooth recirculation at a desired flow rate, which is a necessary condition for dynamic cell culture.

The miniaturization of microfluidic systems plays a pivotal role in achieving portability and compactness. However, conventional microfluidic systems heavily rely on external bulky facilities, such as syringe pumps and compressed air supplies, for continuous flow, which restricts their dissemination across various applications. To address this limitation, micropumps have emerged as a potential solution for portable power supply in microfluidic systems, with piezoelectric micropumps being widely adopted. Nonetheless, the inherent pulsatile mechanism of piezoelectric micropumps leads to unstable flow, necessitating appropriate mitigation for applications requiring flow stability. This research introduces an innovative hybrid pumping system that integrates a wirelessly controlled micropump with a 3D-printed modular microfluidic low-pass-filter. The primary objective of this system is to offer a portable and stable flow source for microfluidic applications. The system design and characterization are based on a three-element circuit model. Experimental results demonstrate a highly stabilized flow rate of 657 ± 7 µL/min. Furthermore, the versatility of the system is showcased by successfully forming droplets with a polydispersity ranging from 1.5% to 4%, comparable to that of bulky commercial pumping systems. This hybrid pumping system offers a promising solution for applications necessitating portable and stable flow sources, and its reconfigurability suggests potential integration into multifunctional microfluidic platforms.

Most of the existing microfluidic chip fabrication techniques are very complex, time-consuming, costly, and are not amenable to mass manufacturing. Impending commercialization of lab-on-a-chip devices demand development of new microfabrication methods that involve least procedural complexities using cost-effective materials. This paper proposes an inexpensive and time-efficient procedure for constructing microfluidic devices on a flexographic sheet which is available as commercial-off-the-shelf material, using a mould-free soft-lithography approach. Microchannel design is transferred to a negative-resist photopolymer sheet (PPS) using collimated ultraviolet (UV) rays and etching is performed to remove unexposed material. The microchannel network is sealed on the top by a photopolymer sheet of the same material and pressure-assisted bonding is performed in the presence of UV. The cross-linking between photopolymers in the mating surfaces ensures relatively high bond strength and perfect sealing. Simple and complex microchannel network with 100–500 (upmu)m width is created using this method and various characterization tests are performed. A functional leakage test ensured that the fabricated chip could withstand 200 kPa pressure at a maximum flow rate of 12 mL/min. Cell culture, biomolecule visualization, and droplet mixing dynamics are studied in the microchip to demonstrate its practical utility. Moreover, a large-area chip with 260 (times) 190 mm(^2) is created using PPS with this three-step method. Most importantly, this method could mass produce 24 microchips with multiple designs within a span of 2 h. In other words, the average time incurred for the fabrication of a single microchip (50 (times) 30 mm(^2)) is less than 5 min. Results suggest that it is a promising method flexible enough to create large-sized chips and to bulk-fabricate microchips having versatile channel designs with high fidelity. Since flexographic infrastructure and materials are very cheap and common in resource-limited settings, the proposed method assumes more importance in the context of rapid commercialization of lab-on-a-chip devices.