Search Results (81)

Rapid and uniform mixing of high-viscosity fluids remains a critical challenge in microfluidics. The inertial effects are strongly suppressed at high viscosity, making it difficult to generate chaotic advection. To address this limitation, a three-dimensional micromixer inspired by the DNA double-helix structure is proposed. The three-dimensional helix microchannel introduces additional torsional forces to generate revolution flows, in addition to the centrifugal forces, which leads to Dean vortices. Fluids not only rotate along the microchannel axis but also revolute along the helix axis. This is analogous to planetary motion, in which a planet spins on its own axis while simultaneously revolving around the sun. Such revolution effects lead to rotation–revolution flows, which significantly enhances chaotic advection. It was found that for 10 cSt silicone oils, the DNA micromixer achieved mixing performance above 98% at Re = 40, outperforming the planar serpentine and splitting-and-recombining (SAR) micromixers. Even for higher-viscosity fluids, the DNA micromixer achieved mixing performance above 95% at Re = 60 for 50 cSt silicone oil and at Re = 120 for 100 cSt silicone oil, whereas that of the traditional passive micromixers fell below 36%. This work demonstrates that the rotation–revolution flows induced by the three-dimensional helix microchannels could effectively intensify chaotic advection, providing an efficient pathway for high-viscosity fluids mixing. Full article

Changing the structures of microchannels has become an effective strategy for improving the mixing performance of passive micromixers. In this study, we propose a novel micromixer with variable section units through changing the geometric parameters including the type, the position, the number, and the ratio of the variable section units. The effects of these geometric parameters on the mixing performance were numerically investigated and parametrically compared. The results showed that the type of Gra channel, the initial position, a number of 4, and the ratio of 1:4 should be selected. With this selected configuration, the mixing efficiency of the micromixer can be significantly enhanced, with the mixing index exceeding 0.96 at a Reynolds number of 100. These findings demonstrate an effective design strategy for developing passive micromixers. Full article

High-efficiency mixing and precise droplet generation are essential for the broad application of microfluidic chips in biology, chemistry, and medicine, with integrated micromixer and microdroplet generator systems playing an increasingly important role in diagnostics and drug detection. This review offers a comprehensive and systematic overview of micromixers and microdroplet generators, covering their classification, working principles, performance characterization, and integration strategies. Passive and active micromixers, the latter employing pressure, electric, acoustic, magnetic, and thermal fields to enhance mixing, are summarized with a critical discussion of their advantages, limitations, and structural optimization. Various droplet generation methods, including crossflow, flow focusing, coflow, step emulsification, and active techniques, are examined alongside key parameters affecting droplet size, monodispersity, and generation frequency. Performance characterization metrics for both components, including mixing efficiency, mixing time, pressure drop, droplet size distribution, generation frequency, and stability, are also discussed. The review then focuses on integration, emphasizing two primary architectural strategies: mixing reagents before encapsulation and inducing mixing within droplets after formation. Synergistic applications in single cell analysis, materials synthesis, and drug screening are presented. Notably, unlike previous reviews that treat micromixers or droplet generators separately, this review uniquely emphasizes architectural integration and critically evaluates the associated trade-offs. Current challenges and future directions, including material selection, fabrication techniques, and practical application-oriented considerations, are also addressed. Full article

Today, microfluidics has become a revolutionary field of engineering due to its wide range of applications, including lab-on-a-chip devices, microscale biochemical reactors, drug delivery systems, and disease diagnostics. Efficient fluid mixing has been a significant challenge in these systems due to the dominance of laminar flow and low-Reynolds number conditions, where mixing relies primarily on slow molecular diffusion. It is very difficult to achieve rapid mixing and homogeneous mixing within a limited length. In this study, a bioinspired passive micromixer is developed based on the cristae architecture of mitochondria, which is known for maximizing surface area and transport efficiency in biological systems. The micromixer incorporates cristae-like microstructures within a straight microchannel to produce continuous flow deflection, stretching, and folding, thereby promoting chaotic advection without relying on external energy sources. It also includes mitochondrial granules, such as micropillars, within the channel to disrupt streamline flow. Thus, a numerical investigation was conducted to design four different micromixer geometries: conventional T-channel, and T-channels with a single, double and triple matrix of cristae. The analysis was performed in COMSOL Multiphysics, in which “Laminar flow” and “Transport of diluted species” physics were used, and a stationary study was executed. Simulations were conducted at different Reynolds numbers (Re = 0.1–100) to observe the feasibility of the proposed designs. For analysis, the mixing index and concentration profiles at the outlet and along the length were also examined. The results showed that the high cristae density channel performed well, achieving a mixing index of 95.85% at Re = 0.1 and 85.84% at Re = 100, proving that the proposed mitochondria-inspired cristae Mito-mixer delivers efficient mixing over a broad Reynolds-number range while maintaining a compact, length-efficient design. Full article

Micromixers are crucial for rapid and homogeneous mixing in lab-on-a-chip systems. This study presents a novel passive micromixer that synergistically combines a Zigzag channel with D-shaped obstacles to enhance mixing across a broad Reynolds number (Re) range of 0.1–50. The design leverages flow splitting, recombination, and the generation of localized high-velocity streams to effectively disrupt laminar flow. A comprehensive parametric study optimized key geometric parameters, including obstacle dimensions (b₂, a₂) and the number of mixing units (n). Results show that optimizing b₂ to 500 μm and increasing a₂ to 250 μm significantly enhances mixing efficiency. Mechanistic analysis reveals that centrifugal forces in the Zigzag channel work synergistically with obstacle-induced perturbations to stretch and fold the fluid interface, promoting transverse transport. The optimized mixer, fabricated and experimentally validated, achieves a high mixing index (>0.85) under all Re conditions. This work provides valuable design insights for developing efficient, compact micromixers for micro-total analysis systems. Full article

Passive micromixers can be used in a wide range of chemical applications for reagent preparation as well as chemical analysis. To investigate a micromixer with high performance under various Re conditions, based on the research of previous scientists, we hereby parameterize three influential factors on the structural design of the micromixer. In this study, we chose five distinct level values from a set of three influential factors of the micromixer, based on the results of a one-way impact analysis to ascertain their degree of influence. For five different Re cases, the Taguchi orthogonal test was performed using the selected five-level values, the fluid mixing efficiency was examined numerically, and we used the orthogonal table L₂₅5⁶. Finally, a set of optimization parameters was selected. An optimized micromixer structural model with high mixing efficiency under different Re conditions has been achieved. The degree of stirring of the optimized micromixer and the comparison curves before and after the optimization were also analyzed. We have also manufactured and tested the micromixer of this design. The simulation results show that the mixing efficiency of “the After Optimized Y-shaped channel Koch fractal Cesàro construction” micromixer (AOYKC) designs in this paper is increased by 15.99%, 21.19%, 19.34%, 11.41%, and 0.04% at Re = 0.1, 1, 10, 20, and 100. Full article

This study introduces the Double-Diamond Reactor (DDR), a novel planar passive microreactor designed to overcome the following conventional limitations: inefficient mass transfer, high flow resistance, and clogging. The DDR integrates splitting–turning–impinging (STI) hydrodynamic principles via CFD-guided optimization, generating chaotic advection to enhance mixing. Experimental evaluations using Villermaux–Dushman tests showed a segregation index ($X_s$) as low as 0.027 at 100 mL·min⁻¹, indicating near-perfect mixing. In BaSO₄ nanoparticle synthesis, the DDR achieved a 46% smaller average particle size (95 nm) and narrower distribution (${\sigma }_g=1.27$) compared to reference designs (AFR-1), while maintaining low pressure drops (<20 kPa at 60 mL·min⁻¹). The DDR’s superior performance stems from its hierarchical flow division and concave-induced vortices, which eliminate stagnant zones. This work demonstrates the DDR’s potential for high-throughput nanomaterial synthesis with precise control over particle characteristics, offering a scalable and energy-efficient solution for advanced chemical processes. Full article

To enhance passive mixing in microchannels, T-shaped double-spiral and serpentine microchannels with identical curvature radii were designed and numerically analyzed across a Reynolds number (Re) range of 1 to 300. The double-spiral microchannel exhibited superior mixing performance at Re ≤ 200, which is primarily attributed to the efficient utilization of Dean vortices. In contrast, the serpentine microchannel showed better performance at Re ≥ 250, benefiting from the early formation of four-vortex structures induced by periodic curvature reversals. To further enhance the performance of the serpentine microchannel at low Re, groove structures with varying orientation angles were incorporated. The introduction of the groove structures generated lateral secondary flows that not only increased flow disturbances but also disrupted the symmetry of the Dean vortices. Among these configurations, Structure 2, with a 45° angle between the groove direction and centrifugal force, exhibited the most pronounced enhancement in vortex intensity, as the secondary flows induced by the grooves synergistically interacted with the Dean vortices. This configuration resulted in the highest mixing enhancement (>50%). This study provides valuable insights into geometry-driven mixing mechanisms and offers design guidelines for high-efficiency micromixers across a wide range of Re. Full article

We propose a novel passive micromixer based on multiple passages and analyze its mixing performance comprehensively. The multiple passages are constructed with straight channels, making them easier to manufacture, compared to conventional SAR micromixers and other micromixers based on curved channels. Its mixing performance has been demonstrated to be superior to that of the previous micromixers across a broad range of Reynolds numbers. Five distinct designs incorporating converging passages were explored to study the significance of the number of passages on the mixing performance. Across a broad range of Reynolds number ranges (0.1 to 80), the two-passage design significantly improved mixing performance, with a degree of mixing (DOM) consistently exceeding 0.84. Particularly, the mixing enhancement is prominent within the low and intermediate range of Reynolds numbers ($\mathrm{R}\mathrm{e}\le 20)$. This enhancement in the regime of molecular diffusion dominance stems from the elongated interface between the two fluids. The mixing enhancement in the transition regime is due to a secondary flow being generated on the cross-section normal to the main stream direction. The intensity of this secondary flow is significantly influenced by the number of multiple passages. The optimal number for the present micromixer design is two. The DOM remains almost constant for the submergence of multiple passages in the range of 40 to 70 (μm). Full article

In recent years, microfluidics has emerged as an interdisciplinary field, receiving significant attention across various biomedical applications. Achieving a noticeable mixing of biofluids and biochemicals at laminar flow conditions is essential in numerous microfluidics systems. In this research work, a new kind of micromixer design integrated with an Archimedes screw is designed and investigated using numerical simulation and experimental approaches. First, the geometrical parameters such as screw length (l), screw pitch (p) and gap (s) are optimized using the Design of Expert (DoE) approach and the Central Composite Design (CCD) method. The experimental designs generated by DoE are then numerically simulated aiming to determine Mixing Index (MI) and Performance Index (PI). For this purpose, COMSOL Multiphysics with two physics modules—laminar and transport diluted species—is used. The results revealed a significant influence of screw length, screw pitch and gap on mixing performance. The optimal design achieved is then scaled up and fabricated using a 3D additive manufacturing technique. In addition, the optimal micromixer design is numerically and experimentally investigated at diverse Reynolds numbers, ranging from 2 to 16. The findings revealed the optimal geometrical parameters that produce the best result compared to other designs are a screw length of 0.5 mm, screw pitch of 0.23409 mm and a 0.004 mm gap. The obtained values of the mixing index and the performance index are 98.47% and 20.15 Pa⁻¹, respectively. In addition, a higher mixing performance is achieved at the lower Reynolds number of 2, while a lower mixing performance is observed at the higher Reynolds number of 16. This study can be very beneficial for understanding the impact of geometrical parameters and their interaction with mixing performance. Full article

Microbial contamination is an important factor threatening the safety of Chinese medicine preparations, and microfluidic detection methods have demonstrated excellent advantages in the application of rapid bacterial detection. In our study, a novel optical biosensor was developed for the rapid and sensitive detection of Salmonella in traditional Chinese medicine on a microfluidic chip. Immune gold@platinum nanocatalysts (Au@PtNCs) were utilized for specific bacterial labeling, while magnetic nano-beads (MNBs) with a novel high-gradient magnetic field were employed for the specific capture of bacteria. The immune MNBs, immune Au@PtNCs, and bacterial samples were introduced into a novel passive microfluidic micromixer for full mixing, resulting in the formation of a double-antibody sandwich structure due to antigen–antibody immune reactions. Subsequently, the mixture flowed into the reaction cell, where the MNBs-Salmonella-Au@PtNCs complex was captured by the magnetic field. After washing, hydrogen peroxide-tetramethylbenzidine substrate (H₂O₂-TMB) was added, reacting with the Au@PtNCs peroxidase to produce a blue reaction product. This entire process was automated using a portable device, and Salmonella concentration was analyzed via a phone application. This simple biosensor has good specificity with a detection range of 9 × 10¹–9 × 10⁵ CFU/mL and can detect Salmonella concentrations as low as 90 CFU/mL within 74 min. The average recoveries of the spiked samples ranged from 76.8% to 109.5% Full article

This study presents an innovative passive micromixer design featuring convergent–divergent sinusoidal walls, evaluated using the Villermaux–Dushman protocol. Five distinct designs were fabricated and tested, demonstrating superior mixing efficiency without additional obstructions. Testing of flow rates from 1000 to 50 mL/h revealed that the square-wave micromixer had the highest efficiency due to repeated fluid perturbations from its 90-degree angles. The loop-wave mixer performed the worst due to its lack of angles. The circular and box-wave mixers outperformed the loop-wave and backward arrow mixers due to their split and recombination effects. These designs, especially the circular and box-wave designs, offer optimal mixing for short-length applications, improving the efficiency and manufacturing simplicity for biomedical and biochemical analyses. Full article

In this study, three-dimensional simulations were conducted on a new passive micromixer to assess the thermal and hydrodynamic behaviors of Newtonian and non-Newtonian fluids subjected to low generalized Reynolds numbers (0.1 to 50) and shear-thinning properties. To acquire a more profound comprehension of the qualitative and quantitative fluctuations in fluid fraction using the CFD Fluent Code, the mass mixing index, rheological behavior, performance index, mixing energy cost, mass fraction distributions, temperature contours, and pressure drop were compared to illustrate the importance of the mixer geometry in the context of two miscible fluids with varying inlet temperatures. The selected geometry is characterized by a robust chaotic flow that substantially enhances thermal and hydrodynamic performance across all Reynolds numbers. A mass mixing exceeding 72.5% is obtained when Re = 5, reaching 93.5% when Re = 50. Furthermore, the evolution of thermal mixing for all behavior indexes reaches a step of 98% with minimal pressure losses. This work enabled the demonstration of a chaotic geometry in a highly efficient mixing system, leading to enhanced thermal performance for both Newtonian and non-Newtonian fluids. The results of the hydrodynamic and thermal characterization of the mixing of shear-thinning fluids within the micromixers under investigation are conclusive. Full article

A novel passive micromixer equipped with circulation promoters is proposed, and its mixing performance is simulated over a broad range of Reynolds numbers ($0.1\le \mathrm{R}\mathrm{e}\le 100$). To evaluate the effectiveness of the circulation promoters, three different configurations are analyzed in terms of the degree of mixing (DOM) at the outlet and the associated pressure drop. Compared to other typical passive micromixers, the circulation promoter is shown to significantly enhance mixing performance. Among the three configurations of circulation promoters, Case 3 demonstrates the best performance, with a DOM exceeding 0.96 across the entire range of Reynolds numbers. At Re = 1, the DOM of Case 3 is 3.7 times larger than that of a modified Tesla micromixer, while maintaining a comparable pressure drop. The mixing enhancement of the present micromixer is particularly significant in the low and intermediate ranges of Reynolds numbers ($\mathrm{R}\mathrm{e}<40).$ In the low range of Reynolds numbers ($\mathrm{R}\mathrm{e}\le 1$), the mixing enhancement is primarily due to circulation promoters directing fluid flow from a concave wall to the opposite convex wall. In the intermediate range of Reynolds numbers ($2\le \mathrm{R}\mathrm{e}<40$), the mixing enhancement results from fluid flowing from one concave wall to another concave wall on the opposite side. Full article

We propose a novel passive micromixer leveraging STC (split-to-circulate) flow characteristics and analyze its mixing performance comprehensively. Three distinct designs incorporating submerged circular walls were explored to achieve STC flow characteristics, facilitating flow along a convex surface and flow impingement on a concave surface. Across a broad Reynolds number range (0.1 to 80), the present micromixer substantially enhances mixing, with a degree of mixing (DOM) consistently exceeding 0.84. Particularly, the mixing enhancement is prominent within the low and intermediate range of Reynolds numbers ($0.1<\mathrm{R}\mathrm{e}<20)$. This enhancement stems from key flow characteristics of STC: the formation of saddle points around convex walls and flow impingement on concave walls. Compared to other passive micromixers, the DOM of the present micromixer stands out as notably high over a broad range of Reynolds numbers ($0.1\le \mathrm{R}\mathrm{e}\le 80$). Full article