Microfluidics and Nanofluidics最新文献

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.

Gold nanostars are valuable materials for nanomedicine, energy conversation, and catalysis. Microfluidic synthesis offers a simple and controlled means to produce nanoparticles as they offer precise fluid control and improve heat and mass transfer. 3D-printed microfluidics are a good alternative to PDMS devices because they are affordable to produce and can be more easily integrated with active mixing strategies. 3D-printed microfluidics has only been applied to the production of silver and gold nanospheres, but not complex structures like gold nanostars. Synthesis of gold nanostars requires highly effective mixing to ensure uniform nucleation and growth. In this work, we present a 3D-printed microfluidic device that utilizes an efficient vibrating sharp-tip acoustic mixing system to produce high-quality and reproducible gold nanostars via a seedless and surfactant-free method. The vibrating sharp-tip mixing device can mix three streams of fluid across ~ 300 μm within 7 ms. The device operates with flow rates ranging from 10 μL/min to 750 μL/min at low power requirements (2–45 mW). The optical properties of the resulting nanotars are easily tuned from 650 to 800 nm by modulating the input flow rate. Thus, the presented 3D-printed microfluidic device produces high-quality gold nanostars with tunable optical and physical properties suitable for extensive applications.

Polydimethylsiloxane (PDMS) is a popular material to rapidly manufacture microfluidic deterministic lateral displacement (DLD) devices for particle separation. However, manufacturing and operation challenges are encountered with decreasing device dimensions required to separate submicron particles. The smaller dimensions, notably, cause high hydraulic resistance, resulting in significant pressure even at relatively low throughputs. This high pressure can lead to PDMS deformation, which, in turn, influences the device performance. These effects may often be overlooked in the design and operation of devices but provide a systematic source of error and inaccuracies. This study focuses in detail on these effects and investigates pillar deformation in detail. Subsequently, we discuss a potential solution to this deformation using thermal annealing to stiffen the PDMS. We evaluate the influence of stiffness on the separation performance at elevated sample flow rates with submicron particles (0.45 and 0.97 µm diameter). An excellent separation performance at high throughput is successfully maintained in stiffer PDMS-based DLD devices, while the conventional devices showed decreased separation performance. However, the increased propensity for delamination constrains the maximal applicable throughput in stiffer devices. PDMS deformation measurements and numerical simulations are combined to derive an iterative model for calculating pressure distribution and PDMS deformation. Finally, the observed separation characteristics and encountered throughput constraints are explained with the iterative model. The results in this study underline the importance of considering pressure-induced effects for PDMS-based DLD devices, provide a potential mitigation of this effect, and introduce an approach for estimating pressure-induced deformation.

The viscous and thermal velocity slip coefficients of various monatomic gases are computed via the linearized classical Boltzmann equation, with ab initio potential, subject to Maxwell and Cercignani–Lampis boundary conditions. Both classical and quantum interatomic interactions are considered. Comparisons with hard sphere and Lennard–Jones potentials, as well as the linearized Shakhov model are performed. The produced database is dense, covers the whole range of the accommodation coefficients and is of high accuracy. Using symbolic regression, very accurate closed form expressions of the slip coefficients, easily implemented in the future computational and experimental works, are deduced. The thermal slip coefficient depends, much more than the viscous one, on the intermolecular potential. For example, in the case of diffuse scattering, the relative differences in the viscous slip coefficient data between HS and AI potentials are less than 4%, whilst the corresponding ones in the thermal slip coefficient data are about 6% for He, reaching 15% for Xe. Quantum effects are considered for He, at temperatures 1–10⁴ K to deduce that deviations from the classical behaviour are not important in the viscous slip coefficient, but they become important in the thermal slip coefficient, where the differences between the classical and quantum approaches reach 15% at 1 K. The computational effort of solving the linearized Boltzmann equation with ab initio and Lennard–Jones potentials is the same. Since ab initio potentials do not contain any adjustable parameters, it is recommended to use them at any temperature.

We present a multiscale method for simulating non-equilibrium lubrication flows. The effect of low pressure or tiny lubricating geometries that gives rise to rarefied gas effects means that standard Navier–Stokes solutions are invalid, while the large lateral size of the systems that need to be investigated is computationally prohibitive for Boltzmann solutions, such as the direct simulation Monte Carlo method (DSMC). The multiscale method we propose is applicable to time-varying, low-speed, rarefied gas flows in quasi-3D geometries that are now becoming important in various applications, such as next-generation microprocessor chip manufacturing, aerospace, sealing technologies and MEMS devices. Our multiscale simulation method provides accurate solutions, with errors of less than 1% compared to the DSMC benchmark results when all modeling conditions are met. It also shows computational gains over DSMC that increase when the lateral size of the systems increases, reaching 2–3 orders of magnitude even for relatively small systems, making it an effective tool for simulation-based design.

Blood plasma is used in more than 90% of blood diagnosis tests, microfluidics devices for separating plasma from whole blood can be utilised to multiple clinical laboratory and point-of-care diagnostics. To separate blood plasma, this research developed a structural design for microfluidic channels. The blood flow behaviour in microchannels has been modelled using the Euler–Euler Laminar Flow Model in COMSOL Multiphysics™. Differently designed microchips with segregating microchannels were created and subjected to investigation. Investigations were done on the geometrical impact of microchannels on plasma separation. Simulation results show that channel model contributes little in displacement or isolating the cells in low flow rate and become a difficult model in the case of blood separation, because it involves capturing the intricate fluid–particle interactions, such as hydrodynamic forces, particle–wall interactions, and particle–particle interactions. Studies on the angle between the main channel and side channels in trifurcation as well as bifurcation, different separator shapes, such as triangular, square, and serpentine, with a focus on the serpentine separator width with outlet bifurcation, show that there is a sudden change in flow direction of the cell free layer to obtain more plasma with a higher purity. By altering the angle of the outlet bifurcation and linearly increasing the diameter of the serpentine, an optimum design with many channels has been presented and evaluated.