Microfluidics and Nanofluidics最新文献

Microchemical devices offer significant advantages for liquid-liquid systems; however, microscale transport in alkane-water systems with large interfacial tension remains poorly understood. This study investigates the dodecane-water system in microchannels to reveal previously unreported aspects of droplet formation, hydrodynamics, and mass transfer. The results demonstrate that droplet size is governed by the interplay between shear and interfacial forces, as well as the flow rate of the dispersed phase, highlighting behaviors not observed in conventional systems. The volumetric mass-transfer coefficient is also determined and correlated with dimensionless numbers. The superficial mass-transfer coefficient was further extracted from experimental results and shown to be strongly influenced by internal convection within slugs. These findings provide new insights into microscale transport phenomena and offer guidance for the optimization of microchemical processes in alkane-water systems.

We describe an approach to enhancing microfluidic mixing by generating acoustic microstreaming flows around microposts in a microfluidic device. Specifically, we synthesize microposts with various cross-sectional shapes (i.e., circles, triangles, and stars) using photocrosslinkable polymers, allowing for precise control over their geometry. We also ensure unobstructed micropost vibration via carefully designed gaps between the microposts and the channel ceiling. Experimental findings reveal that the shape of microposts is critical in influencing microstreaming patterns and mixing efficiency. Circular microposts generate semi-symmetrical circular vortices, resulting in superior mixing performance (86.7%). In contrast, star-shaped microposts, despite having sharper edges and forming pairs of microvortices around their vertices, produce the lowest mixing performance (56.5%). This trend correlates with the microposts’ moment of inertia (MOI); circular posts exhibit the lowest MOI and thus oscillate more readily, whereas star-shaped posts are geometrically more resistant to bending, limiting vibration amplitude and reducing streaming strength. Further characterization of the microstreaming flow patterns in a static aqueous solution reveals that the lower mixing performance of star-shaped micropillars is likely due to the impact of the spacing between the microposts and the emergence of counter-rotating pairs of microvortices, leading to destructive interference. Triangular microposts exhibit moderate mixing performance, generating a pair of opposing vortices around each vertex. Increasing the actuation voltage and reducing the flow rates further improves mixing across all micropost shapes. These findings highlight the significance of micropost design and arrangement in enhancing the performance of microfluidic acoustic mixers.

Capillarity is a key mechanism for fluid control in microfluidic devices, enabling, for example, liquid movement without external pumps. This study develops and validates an analytical model to describe the velocity and displacement of the liquid meniscus in three-dimensional microfluidic channels with walls exhibiting different wettability. Particular focus is placed on the transient behavior of the meniscus during the initial phases of channel filling, a critical yet often overlooked aspect for optimizing flow control. This is especially relevant given the growing adoption of capillary pumps and valves in microfluidic systems. To evaluate the validity and reliability of the proposed model under diverse operating conditions, channels with different geometries and dimensional ratios were fabricated using various materials and techniques. Experimental results confirm the model’s accuracy, even in complex configurations, with relative errors ranging from 7(%) to 10(%).

Droplet-based microfluidics has emerged as a core technology in developing Lab-On-A-Chip systems thanks to miniaturization, rapid analytical response, and low cross-contamination risk. As a result, detecting and characterizing dispersed phases is crucial across several applications, including biological research, drug development, clinical diagnostics, and the synthesis of micro/nanoparticles. Despite efforts to achieve high sensitivity, specificity, speed, and robustness, current fabrication technologies remain challenging, costly, and complex, which limits broader adoption. Thus, this work presents the design and fabrication of a modular droplet-based sensor system integrating off-the-shelf electronic components and PMMA-based flow-focusing microfluidic chips. The system employs an optical light source and light detector for detection, counting, and characterizing water-in-oil systems, enabling on-chip measurement of droplet length, volume, and monodispersity. Experimental validation demonstrated high accuracy, with a 2.06% error rate and a coefficient of variation of 2.35%, confirming stable and monodisperse droplet generation across multiple channel widths. Furthermore, the proposed sensor system offers an affordable, user-friendly, and easy-to-fabricate modular design, with an easily interchangeable microfluidic module. These findings support the development of an ASSURED (Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, and Deliverable to end-users) Lab-on-PCB system.

Although point-of-care testing (POCT) chips offer the advantages of fluid manipulation without external energy and easy portability, they exhibit significant variability in fluid control due to individual operational differences. Therefore, this study developed a finger-actuated quantitative drive module, achieving quantitative fluid driving through its bolt-driven component screwing mechanism, spring return motion, and designed contact point size. The quantitative relationship between its key parameters and fluid-driven volume was elucidated through experiments, providing a theoretical basis for flow control. In addition, we further systematically characterize the consistency of this module’s driving performance. The results indicate that under a single-contact condition, the standard deviation of the single-drive volume for different operators is less than 5%. When using multi-contact parallel control, the maximum volume deviation of each contact is only 0.12 µL, demonstrating good consistency in parallel control. Finally, we integrated the module into our independently developed blood type detection chips and verified its excellent multi-fluid mixing ability through dual color tracing experiments. In double-blind blood type detection experiments, it was able to obtain blood type determination results consistent with traditional test tube methods within 5 min. This work provides an innovative solution for fluid quantitative drive control of POCT chips and demonstrates significant application potential in medical scenarios such as bedside diagnosis and on-site testing.

The fabrication of microfluidic chips using mechanical micromilling offers a promising method for rapid prototyping. This study investigates the use of mechanical micromilling to produce microchannels in Polymethyl methacrylate for flocculant testing, which requires precision and smooth surfaces to ensure effective fluid flow and mixing. The dimensional accuracy of the fabricated microchannels was evaluated using a coordinate measuring machine, and surface quality was analysed through scanning electron microscopy and confocal microscopy. The coordinate measuring measurements indicated high consistency across most features, but significant deviations were observed in specific regions, suggesting challenges in achieving tight tolerances for certain geometric features. The scanning electron micrographs analysis revealed surface imperfections, including excess burrs and feed marks, which could negatively impact fluid flow in microchannels. Confocal microscopy confirmed the presence of high surface roughness, with pronounced peaks and valleys that could disrupt flow and increase resistance in microfluidic applications. The findings highlight the need to optimise process parameters to improve surface quality. Optimisation of the micromilling parameters and post-processing techniques is necessary to enhance surface quality for the microfluidic device to meet the stringent requirements necessary for effective flocculant testing.

The use of shaped microchannels has become increasingly prevalent in heat engine and microelectronics industries due to their exceptional heat dissipation efficiency. However, limited research has addressed the evaporation characteristics of special-shaped capillaries under inclined orientations. At the capillary scale, the effects of gravity and surface tension are comparable, making their interplay particularly relevant. This study investigates the combined impact of gravity and capillary driving forces on the ethanol evaporation characteristics at the opening of triangular capillary tubes with different inclination angles. The temperature distribution and morphological changes of the meniscus during evaporation were explored using infrared thermography and video microscopy. Additionally, the internal flow structure of the meniscus was analyzed using particle image velocimetry technique (PIV). Comparisons were made among the evaporation characteristics at the opening of capillary tubes with different inclination angles (0°, 30°, 60°, and 90°) and cross-sectional shapes (circular and triangular). The results show that the inclination angle of triangular capillary tubes significantly influences the liquid level, corner liquid film thickness, temperature distribution, and flow pattern during ethanol evaporation. Increased inclination angle reduces the corner liquid film thickness, enhances heat transfer efficiency, and accelerates the evaporation rate. However, when the corner liquid film becomes excessively thin, liquid supply is impeded, which hinders the overall evaporation process. The fastest evaporation rate is observed at an inclination angle of 60°, accompanied by the lowest and most uniform temperature distribution at the meniscus.

Understanding the transport behavior of micron-sized particles in the respiratory zone is crucial for assessing health effects of inhaled aerosols, including environmental pollutants and therapeutic drugs. However, experimentally capturing the detailed trajectories of aerosol particles entering the alveoli and understanding the underlying mechanisms of particle transport remain to be further studied. This study experimentally and numerically investigated the detailed trajectories of microparticles transported by alveolar airflows across a range of Reynolds number (Re) conditions. These trajectories clearly illustrate how particles enter and become trapped in the alveoli during both inhalation and exhalation. This study also highlights the critical influence of flow Re, particle diameter, and initial particle position on particle transport behavior. At higher Re, flows tend to drive particles, those near the duct wall, deep towards the alveolar center in spiral paths. Smaller particles (< 1.5 µm) exhibit prolonged suspension, enabling deeper lung penetration. Moreover, in the low-Re alveolar region, particles initially positioned close to the alveoli have an advantage in entering the alveoli and being trapped. This research offers valuable data for improving our understanding of particle transport behavior within the alveolar region, and has potential implications for drug delivery applications.

Milk adulteration is a significant issue, particularly in regions where food safety regulations are weak or inadequately enforced. A cost-effective and straightforward paper-based lab-on-a-chip (LOC) microfluidic device has been developed using a technique known as selective wax impregnation. This technology is advantageous as it requires neither costly equipment nor specialised workers. It can detect prevalent milk adulterants such as urea, detergent, boric acid, soap, and hydrogen peroxide by a combination of chemiluminescent and colorimetric chemical reactions. This provides both visual and quantitative results. A crucial aspect of this technique is its utilisation of a smartphone to capture images, which are subsequently processed on-site using ImageJ software. This device effectively enhances food safety in resource-limited areas and facilitates community-level quality control without dependence on centralised laboratories. It is user-friendly, portable, and cost-effective to produce.

We present a new microfluidic method for the characterization of emulsion stability against coalescence within a microfluidic droplet-making device. In our device, the merging of droplets can be actively controlled under a wide range of flow conditions, using a simple structure. The new method combines features of already existing passive and active methods, hence we refer to it as a “hybrid” method. Our hybrid method allows for a relatively easy integration within any PDMS (polydimethysiloxane)-based microfluidic device comprising a droplet-making structure, since it employs a simple single-layer PDMS geometry. The main device structure comprises 2 pressure chambers, placed symmetrically along a locally expanded main channel, through which the droplets are flowing. By inducing an overpressure in the pressure chambers, a change of the cross-sectional area of the main channel is reached, which influences the droplets’ velocities and their mutual distance, and thus the coalescence rate. To test our hypotheses on the working principle of the device and to test its performance, we carry out systematic experiments at varying flow rates and applied pressures. These experiments confirm the hypothesized working principle of the device and indicate that the method is suitable for characterizing emulsion stability. Moreover, we show that the hybrid method is capable of actively controlling the creation of on-demand coalescence patterns and even of triggering specific single coalescence events. This indicates that the hybrid method, when integrated into a droplet-making device, can offer a promising approach both for characterizing the stability of emulsions and for controlling on-demand droplet coalescence.