Microfluidics and Nanofluidics最新文献

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.

Micromixers become the core elements of lab-on-chip (LOC) devices used for mixing fluid samples at a very small scale. For modest Reynolds numbers, the nature of fluid movement is laminar across the microchannel hence mixing is challenging. Numerous designs of micromixers for mixing enhancement inside microfluidic devices have been developed to solve this issue. The current investigation looks at the performance of two distinct versions of passive micromixers i.e. simple T micromixer (STMM) and vortex T micromixer (VTMM), employing different angular configurations (i.e. 30°, 60°, 90°, 120° and 150°) on their inlet channel to monitor the consistency of blending for the Reynolds number in a range of 10–150. Numerical investigations were done by performing simulations on these geometrical arrangements to evaluate the level of mixing, pressure gradient and cost of mixing. The outcome indicates the performance of mixing is dependent on the angular arrangement of inlet channels. For STMM, the layout with inlet channels at 120° performs most effectively, whereas, for VTMM, the configuration with inlets at 90° performs best.

In this article, we discuss the bioinspired peristaltic pumping mechanism of an elastic non-Newtonian fluid whose rheology is characterized by the Phan-Thien-Tanner model in a microfluidic configuration. We consider the effect of an electroosmotic body force originating from electrical double layer phenomena formed in the wall of the fluidic channel of finite length. The considered configuration is consistent with the natural contraction of the oesophagus wall that does not involve expansion beyond the stationary boundary. Employing lubrication theory and assuming the underlying flow to be in the creeping flow regime, we outline the transport equations pertaining to the chosen peristaltic set up. The transport equations are then solved using a well-established method consistent with perturbation technique. By depicting the pressure variation and wall shear stress graphically for a continuous wave train, we aptly discuss the time-averaged net throughput and flow developed at channel inlet of the chosen pathway and demonstrate the eventual consequences of these flow patterns for a window of viscoelastic and electrokinetic parameters. The outcomes obtained from this model establishes that the underlying flow owing to the peristaltic pumping mechanism strongly relies on the rheological parameter (varepsilon W{e}^{2}). These inferences are expected to be of extensive importance in designing peristalsis pump, mimicking features of the physiological system, for achieving unidirectional flow of complex fluids with improved efficiency, frequently used in biochemical/biomicrofluidic applications.

The encapsulation of cells within droplets is a crucial aspect of various cell analysis applications. Current research has focused on accurately detecting and identifying cell types or cell counts within droplets using object detection in bright-field images. However, there are only a few in-depth investigations into the impact of the image data quality acquired from optical systems on computer vision models. This study examines several popular machine learning object detection models to analyze scenarios complicating the identification of bead locations within a droplet, posing challenges for computer vision models. A microfluidic droplet generation system was developed and implemented, coupled with optical devices to capture images of encapsulated beads within the droplet. To identify the most efficient model, a specific dataset was meticulously selected from the overall data, encompassing images depicting overlapping beads and edge-drifting scenarios. The proposed method achieved up to 98.2% accuracy on the testing dataset and 95% in real-time testing with the YOLOv8 model, enhancing bead count precision within droplets and clarifying the correlation between accuracy and frame recognition thresholds. This work holds particular importance in single-cell sorting, where precision is critical in ensuring meaningful outcomes, particularly concerning rare cell types such as cancer cells.