Microfluidics and Nanofluidics最新文献

A compelling solution to the issue of high heat flux generated by flexible electronic devices has been found in liquid-based microfluidic cooling devices. It has been earlier realized that the varying microchannel hydrodynamics influences the overall heat transfer in these devices. However, microfluidic cooling devices that incorporate intricate microchannels have not been explored to their full potential. In this study, we investigate the use of 3-D intricate microchannel geometries in microfluidic heat sinks, their generated hydrodynamics, and their profound impact on the overall heat transfer process. Utilizing 3D-printed scaffold removal technology, three distinct microfluidic devices were fabricated, each distinguishable by its cross-sectional shape of the microchannel designs (coil, square, and triangle). These microfluidic devices, based on Polydimethylsiloxane-Graphene oxide (PDMS-GO) as substrate material, have been examined experimentally and numerically for their heat dissipation capacities under constant temperature heat source of 358 K at flow rates ranging from 40 to 400 μL/min. Experimental observation illustrates that the coil-microchannel configuration exhibited superior heat dissipation capabilities, outperforming both the square and triangle microchannels across all flow settings. Furthermore, numerical simulations corroborated this experimental finding by providing insights into through-plane temperature distribution, heat transfer coefficient, pressure drop, and channel hydrodynamics. Our study intends to advance the understanding of microchannel cooling, as well as emphasizes the importance of geometrical configuration towards optimal electronic hotspot cooling.

Cylindrical column with packed stationary phase is the workhorse of liquid chromatography systems. These stationary phases are commonly classified on the basis of different form factors namely, beads and monoliths for protein chromatography. Monolithic rods are one of the important geometries derived from polymers through complex polymerization schemes with additional requirements such as cross-linkers and specific reaction conditions. To address these practical difficulties and enable ease of fabrication at laboratory scale, acrylic copolymers are hypothesized to perform as a monolithic stationary phase suitable for protein chromatography. The present work proposes a rapid fabrication technique to obtain monolithic rods that could be reconditioned without any of the above additional steps. It is characterized with monolith diameter that could be controlled using acrylic copolymer concentration. Formation of the copolymeric stationary phase inside microchannel led to annular geometry and in turn, demonstrated fabrication of moon-shaped channels (MSCs) for the first time in literature. An online monitoring system facilitated tracer breakthrough analysis with MSCs to report sharp peak front and an estimate of channel void volume. Breakthrough curves with single protein validated the selection of blue dextran as tracer and indicated retention of proteins due to electrostatic interactions on the functional copolymer surface.

We developed a surface-enhanced Raman scattering (SERS)-active plasmonic core-satellite nanostructure and incorporated it into a membrane filter-integrated microfluidic device for continuous monitoring of molecules in solution. The core-satellite nanostructures were fabricated by immobilizing a high number density of gold nanoparticles (AuNPs) on silica beads.to create many nanogaps among the AuNPs. The sizes of the nanogaps were fine-tuned by adding a silver (Ag) shell to optimize the SERS activity. In addition, citrate molecule, the capping agent of the nanoparticles, was displaced by alkali halides. The displacement not only reduced the SERS signals of citrate but also enhanced the adsorption of target molecules. The alkali halide-treated core-satellite nanostructures were accumulated onto a membrane filter integrated into a microfluidic device, serving as a uniform and sensitive SERS substrate. By increasing the volume of the sample solution flowing through the membrane filter, we increased the number of molecules adsorbed to the nanostructures, amplifying the intensities of their characteristic Raman peaks. Our microfluidic SERS device demonstrated continuous SERS detection of malachite green at a concentration as low as 500 fM. In summary, while various core-satellite nanostructures and microfluidic SERS devices have been reported, the integration of the membrane filter-containing microfluidic device with the core-satellite nanostructures facilitated sensitive and continuous molecule detection in our study.

Interface tracking simulations of gas–liquid Taylor flow in horizontal square microchannels were carried out to understand the relation between the pressure drop in the bubble part and the curvatures at the nose and tail of a bubble. Numerical conditions ranged for 0.00159 ≤ Ca_T ≤ 0.0989, 0.0817 ≤ We_T ≤ 25.4, and 8.33 ≤ Re_T ≤ 791, where Ca_T, We_T, and Re_T are the capillary, Weber, and Reynolds numbers based on the total volumetric flux. The dimensionless pressure drop in the bubble part increased with increasing the capillary number and the Weber number. The curvature at the nose of a bubble increased and that at the tail of a bubble decreased as the capillary number increased. The variation of the curvature at the tail of a bubble was more remarkable than that at the nose of a bubble due to the increase in the Weber number, which was the main cause of large pressure drop in the bubble part at the same capillary number. The relation between the bubble velocity and the total volumetric flux was also discussed. The distribution parameter of the drift-flux model without inertial effects showed a simple relation with the capillary number. A correlation of the distribution parameter, which is expressed in terms of the capillary number and the Weber number, was developed and was confirmed to give good predictions of the bubble velocity.

Microfluidic devices have been widely used to measure the diffusion coefficients and hydrodynamic radii of various molecules, especially proteins. The existing devices that use diffusion-based gradient generation apply obstacles such as membranes or hydrogels to avoid additional fluid flow affecting the evolution of concentration distribution and precise measurement. Here, a free-diffusion based microfluidic device was developed which is capable of measuring the diffusion coefficients of various, different-sized proteins and dyes without using any obstacles by minimizing pressure differences due to its symmetrical geometry. The fluorescent detection and the ease of application of the device enable accelerated measurements and interpretation of results. Time-lapse pictures of 30 s were taken of the diffusion profiles and a custom-made self-written Python program was used to fit the profiles to the theoretical functions and calculate the diffusion coefficients. Diffusion coefficients of bovine serum albumin, immunoglobulin G and rhodamine B were determined with this method and compared to their theoretical and experimental values.

The aim of this study was to prepare, characterize and evaluate liposomes co-encapsulated with curcumin and quercetin using a droplet-based microfluidic device. Curcumin and quercetin co-encapsulated liposomes made of phosphatidylcholine and cholesterol were synthesized using a droplet-based microfluidic device with different flow rate ratios of 9:1, 6:1, 3:1 and 1:1 of the aqueous to organic phase at 100 to 160 µl/min flow rate. The dynamic light scattering technique showed that 9:1 and 6:1 flow rate ratios at 140 and 160 µl/min flow rates, respectively provide desired particle size range of 200–250 nm and 0.17–0.23 polydispersity index. The greatest encapsulation and loading efficiency achieved for curcumin and quercetin was 68 ± 9.2%, 14 ± 1.8%, and 36 ± 2.7%, 7.2 ± 0.5%, respectively with 6:1 flow rate ratio. Cell uptake studies performed on human oral carcinoma cells, FaDu using confocal laser scanning microscopy showed that the liposomes were taken up within 2 h. Clathrin and caveolin-mediated pathways contribute to the cell uptake of liposomes. The FaDu cell viability was reduced to 49 ± 2.2, 69 ± 1.5 and 47 ± 3.5% after incubation with liposomes containing curcumin (80 µM), quercetin (86 µM) and combination (32 µM of curcumin and 26 µM of quercetin), respectively. Apoptosis assay showed that the combination liposomes inhibit FaDu cell growth through apoptosis induced cell death. In conclusion, co-encapsulated liposomes can be prepared by microfluidics-based method and curcumin and quercetin combination liposomes are effective against oral carcinoma.

Graphical Abstract

Accommodation Coefficients (ACs) are used in slip models to determine some important parameters for flowing dilute gases on solid surfaces such as: Cercignani–Lampis–Lord (CLL) model, drag coefficient, slip velocity, shear stress, and temperature jump. These coefficients in slip, transitional, and free molecular flow regimes take values other than unity. As a result, determining these coefficients for different gases and surfaces is crucial, especially where the continuum assumption with no-slip conditions at the surface is inaccurate. These coefficients can be extracted using experimental and simulation methods with different techniques. This paper provides a review of studies that have been conducted to determine the ACs, with a particular focus on the tangential momentum accommodation coefficient (TMAC), using both experimental and simulation methods. The research mainly pertains to microfluidics and nanofluidics. The reviewed studies have concluded that there is no clear relationship between the molecular weight of a gas and it’s TMAC. Also, the values of ACs depend on various factors.

Microfluidics is an area that allows the design and construction of microchips. The most common fabrication of these chips is expensive and difficult to access, requiring a specialized laboratory, with instruments that need to be monitored by experienced technicians and high-cost materials, then new techniques are sought to facilitate their production. Here, we present a fabrication methodology that combines the 3D printer resolution, and the polydimethylsiloxane flexibility to create hydrophobic and biocompatible microfluidics chips which are connected to a microfluidic control system. Transparent, and leak-free polydimethylsiloxane microchips were achieved with a width and a height of 250 µm. This strategy allows to produce at least, 20 chips using the same resin mold. The pressure at which the chip can work is from 2.4 kPa to 124 kPa. This work provides a low-cost alternative for academic and research groups to create their own microfluidic systems and use the microfluidic advantages in all types of applications including biosensor building, studies in medicine, biology, nanoscience, environmental technology, chemistry, etc., since it allows a controlled manipulation of one or more fluids in a certain area where a sensor can be placed, generate a reaction, among others.

Alginate-based microcapsules are promising carriers for drugs and biomedical agents due to their biodegradability, biocompatible character, and easy availability. Through microfluidic technology, we've achieved highly uniform alginate microencapsulation, exhibiting remarkable monodispersity. Despite alginate's favorable attributes, such as biocompatibility, its limited stability and mechanical properties pose challenges for drug delivery applications. Our research addresses this limitation by introducing a cross-linked alginate/kappa-carrageenan (Alg/κ-Car) co-polymer, enabling the fabrication of microgels through microfluidic devices. Our study demonstrates significant enhancements in Alg microgel properties with the incorporation of κ-Car. Comparative analyses of Alg/κ-Car and Alg microgels revealed substantial improvements in morphology, gel network, and stability attributed to the κ-Car addition. Notably, loading BSA as a model protein showcased enhanced drug carrier capabilities of the microgel when κ-Car was present. The release half-life of BSA within 1.5 wt.% Alg microgel was approximately 1.5 h, which extended to about 3 h when substituting 0.5 wt.% of Alg with κ-Car. This shift signifies a more controlled BSA release.

Graphical abstract

Focusing and separation of cells by microfluidic techniques are significant steps in many applications, such as single-cell analysis and disease diagnosis. Among the microfluidic techniques, passive magnetophoresis, as a label-free manner, can manipulate samples by means of magnetic field. Nowadays, most magnetic fields are generated by permanent magnets and electromagnets with large size. However, it is difficult to assemble a magnetic array using permanent magnets or electromagnets to optimize the field distribution. To produce a flexible magnetic field, a micro-magnet made by NdFeB powder and polydimethyl siloxane is proposed in this paper, and those magnetized micro-magnets are arranged into different arrays according to the arrangements of their magnetization directions. Meanwhile, a microfluidic chip containing magnetized micro-magnet arrays is designed for focusing and separating polystyrene microbeads with different diameters. The focusing and separation behaviors of microbeads in the designed microfluidic system are numerical and experimental investigated. In addition, the effects of flow rate and the arrangement of the magnetic micro-magnet array on microbead focusing and separation are discussed. Finally, a multistage microfluidic chip is designed to successfully isolate 5 μm-diameter, 10 μm-diameter, and 15 μm-diameter microbeads from their mixture at a flow rate of 240 μL/min with high purity.