Search Results (227)

Phase-change microcapsules offer significant advantages for thermal energy storage and regulation. However, conventional mechanical agitation fabrication methods encounter difficulties in achieving monodispersity, precise size control, and structural uniformity. Droplet microfluidics emerges as a promising alternative, enabling controllable production of microcapsules with tunable sizes (1–1000 μm), programmable core–shell configurations, and high encapsulation efficiency. This review comprehensively summarizes recent advances in microfluidic strategies for phase-change microcapsules fabricating, including single encapsulation, multi-core encapsulation, and high-throughput parallelization and their applications in solar energy storage, building thermal regulation, electronics cooling, and smart textiles. The review highlights key challenges for future advancement which will unlock the full potential of microfluidics-engineered phase-change microcapsules in next-generation thermal energy technologies. Full article

In this work, we investigate the fundamental usability of fluorescent DNA-templated silver nanoclusters (DNA-AgNCs) as sensors for Point-of Care-Testing (PoCT) applications. We developed a microfluidic platform for the generation of droplets containing DNA-AgNCs in defined, different chemical environments. The droplets are read out fluorescently at two different emission wavelengths. For the pre-evaluation for the usage of biologically relevant matrices with DNA-AgNCs, the response of two different DNA-AgNCs to a variation in pH and sodium chloride concentration was acquired. Our compact and simple setup can detect DNA-AgNCs well below 100 nM and allows the characterization of the fluorescence response of DNA-based biohybrid nanosensors to changes in the chemical environment within short measurement times. The model DNA-AgNCs remain fluorescent throughout the physiologically relevant chloride concentrations and up to 150 mM. Upon shifts in pH, the DNA-AgNCs showed a complex fluorescence intensity response. The model DNA-AgNCs differ strongly in their response characteristics to the applied changes in their environments. With our work, we show the feasibility of the use of DNA-AgNCs as sensors in a simple microfluidic setup that can be used as a building block for PoCT applications while highlighting challenges in their adaption for use with biologically relevant matrices. Full article

Microfluidics is a rapidly advancing field focused on optimizing microdevices for applications such as organ-on-a-chip systems and enhancing laboratory analyses. Understanding the physical parameters of droplet generation is crucial for these devices. Computational fluid dynamics (CFD) techniques are essential for providing insights into the limitations and efficiency of numerical methods for studying fluid dynamics and improving our understanding of various application conditions. However, the influence of different numerical methods on the analysis of physical parameters in problems involving droplet generation in microchannels remains an area of ongoing research. This study implements the Volume of Fluid (VOF) method to investigate key physical parameters, including droplet size and the effect of the capillary number on fluid regimes, in droplet generation within a microchannel featuring a T-junction geometry. We compare the VOF method with the widely used Level Set Method (LSM) to evaluate its suitability for this context. The results show that the VOF method agrees with the LSM in fundamental outcomes, such as the reduction in droplet diameter as the flow rate ratio increases and the identification of the capillary number’s influence on fluid regime classification. The VOF method provides a clearer understanding of transitions between fluid regimes by detecting stages of non-uniformity in droplet size. It identifies a transition region between regimes with variations in droplet size, proving to be effective at mapping fluid flow regimes. This study highlights the potential of the VOF method in offering more detailed insights into instabilities and transitions between fluid regimes at the microscale. Full article

This study proposes a simple yet versatile microfluidic strategy for fabricating monodisperse alginate hydrogel microspheres using a symmetric flow-focusing device. The system integrates three key innovations: (1) Cost-effective mold fabrication: A paper-based positive master replaces conventional SU-8 photoresist, significantly simplifying device prototyping. (2) Surfactant-free droplet generation: Alginate hydrogel droplets are formed at the first flow-focusing junction without requiring interfacial stabilizers. (3) In situ solidification with coalescence suppression: Acetic acid-infused corn oil is introduced at the adjacent junction, simultaneously triggering ionic crosslinking of alginate via pH reduction while preventing droplet aggregation. Notably, the hydrogel microspheres can be efficiently harvested through oscillatory aqueous phase separation, removing post-fabrication washing steps (typically 6–8 cycles for surfactant and oil removal). This integrated approach demonstrates exceptional advantages in fabrication simplicity, process scalability, and operational robustness for high-throughput hydrogel microsphere production. Full article

Flexographic printing, traditionally used in the packaging industry, has emerged as a promising technology for microfluidic device fabrication due to enabling high resolution and being commercially available at a low cost compared to conventional techniques. This review explores the adaptation of a photopolymer flexographic printing plate mold (FMold) for microfluidics, examining its advantages, challenges, and applications. It offers a state-of-the-art view of the application of FMold for microfluidic systems, which offers a unique opportunity in terms of cost-effectiveness, scalability, and rapid prototyping. Applications are diverse: FMold has enabled the fabrication of microfluidic devices used in enhanced oil recovery to prepare rock-on-a-chip models, droplet generation and storage, suspension cell culture, monoclonal antibody production, complex cell differentiation pattern creation, phage screening, drug screening, cell detection, and cancer stem cell culture. Since its first appearance in 2018, FMold has been utilized in 50 publications in different laboratories around the world. Key advancements, current research trends, and future prospects are discussed to provide a comprehensive overview of this evolving tool. Full article

Rapid mixing is widely prevalent in the field of microfluidics, encompassing applications such as biomedical diagnostics, drug delivery, chemical synthesis, and enzyme reactions. Mixing efficiency profoundly impacts the overall performance of these devices. However, at the micro-scale, the flow typically presents as laminar flow due to low Reynolds numbers, rendering rapid mixing challenging. Leveraging the vortices within a droplet of the Taylor flow and inducing chaotic convection within the droplet through serpentine channels can significantly enhance mixing efficiency. Based on this premise, we have developed a droplet micromixer that integrates the T-shaped channels required for generating Taylor flow and the serpentine channels required for inducing chaotic convection within the droplet. We determined the range of inlet liquid flow rate and gas pressure required to generate Taylor flow and conducted experimental investigations to examine the influence of the inlet conditions on droplet length, total flow rate, and mixing efficiency. Under conditions where channel dimensions and liquid flow rates are identical, Taylor flow achieves a nine-fold improvement in mixing efficiency compared to single-phase flow. At low Reynolds number (0.57 ≤ Re ≤ 1.05), the chip can achieve a 95% mixing efficiency within a 2 cm distance in just 0.5–0.8 s. The mixer proposed in this study offers the advantages of simplicity in manufacturing and ease of integration. It can be readily integrated into Lab-on-a-Chip devices to perform critical functions, including microfluidic switches, formation of nanocomposites, synthesis of oxides and adducts, velocity measurement, and supercritical fluid fractionation. Full article

Droplet-based microfluidics (DBM) has emerged as a powerful tool for a wide range of biochemical applications, from single-cell analysis and drug screening to diagnostics and tissue engineering. This review provides a comprehensive overview of the latest advancements in droplet generation and trapping techniques, highlighting both passive and active approaches. Passive methods—such as co-flow, cross-flow, and flow-focusing geometries—rely on hydrodynamic instabilities and capillary effects, offering simplicity and integration with compact devices, though often at the cost of tunability. In contrast, active methods exploit external fields—electric, magnetic, thermal, or mechanical—to enable on-demand droplet control, allowing for higher precision and throughput. Furthermore, we explore innovative trapping mechanisms such as hydrodynamic resistance networks, microfabricated U-shaped wells, and anchor-based systems that enable precise spatial immobilization of droplets. In the final section, we also examine active droplet sorting strategies, including electric, magnetic, acoustic, and thermal methods, as essential tools for downstream analysis and high-throughput workflows. These manipulation strategies facilitate in situ chemical and biological analyses, enhance experimental reproducibility, and are increasingly adaptable to industrial-scale applications. Emphasis is placed on the design flexibility, scalability, and biological compatibility of each method, offering critical insights for selecting appropriate techniques based on experimental needs and operational constraints. Full article

Conventional laboratory methods for handling valuable biological samples typically use pipettes or needles, which are prone to issues such as dead volume and sample waste. Furthermore, the sampling and processing of pathogenic bacteria, such as Escherichia coli (E. coli) in environmental wastewater, require labor-intensive procedures with multiple complex steps. To overcome these limitations, we developed a pipette integrated with a microfluidic chip for bacteria sampling and delivery. This pipette can provide the negative pressure to microfluidic chips for sampling, the constant temperature unit for biological reaction, and programs for automatic control (suction, heating, liquid discharge, and cleaning) and display. The droplet chip employs a cross-channel structure to generate droplets and incorporates a designated droplet storage and detection area. Utilizing this innovative device, we have demonstrated the generation, transportation, and storage of pL droplets, as well as quantitatively detected E. coli samples across various concentrations. The test results have demonstrated the overall reliability and data consistency of the system. Overall, our device achieves the precise sampling of pL volumes, offering a simple yet promising solution for the sampling and delivery of bio-samples in remote settings. Full article

Concentration gradient generation plays a pivotal role in advancing applications across drug screening, chemical synthesis, and biomolecular studies, yet conventional methods remain constrained by labor-intensive workflows, limited throughput, and inflexible gradient control. This study presents a novel multilayer microfluidic chip leveraging shear flow-driven partitioning–recombination mechanisms to enable the flexible and high-throughput generation of concentration gradient droplets. The chip integrates interactive upper and lower polydimethylsiloxane (PDMS) layers, where sequential fluid distribution and recombination are achieved through circular and radial channels while shear forces from the oil phase induce droplet formation. Numerical simulations validated the dynamic pressure-driven concentration gradient formation, demonstrating linear gradient profiles across multiple outlets under varied flow conditions. The experimental results revealed that the shear flow mode significantly enhances mixing uniformity and droplet generation efficiency compared to continuous flow operations, attributed to intensified interfacial interactions within contraction–expansion serpentine channels. By modulating hydrodynamic parameters such as aqueous- and oil-phase flow rates, this system achieved tunable gradient slopes and droplet sizes, underscoring the intrinsic relationship between flow dynamics and gradient formation. The proposed device eliminates reliance on complex channel networks, offering a compact and scalable platform for parallelized gradient generation. This work provides a robust framework for optimizing microfluidic-based concentration gradient systems, with broad implications for high-throughput screening, combinatorial chemistry, and precision biomolecular assays. Full article

Hydrogel particles are essential in biological applications because of their distinctive capacity to retain water and encapsulate active molecules within their three-dimensional structure. Typical particle sizes range from nanometers (10–500 nm) to micrometers (1–500 µm), depending on the specific application and method of preparation. These characteristics render them optimal carriers for the administration of active compounds, facilitating the regulated and prolonged release of pharmaceuticals, including anticancer agents, antibiotics, and therapeutic proteins. Hydrogel particles can exhibit various morphologies, including spherical, rod-shaped, disk-shaped, and core–shell structures. Each shape offers distinct advantages, such as improved circulation time, targeted drug delivery, or enhanced cellular uptake. Additionally, hydrogel particles can be engineered to respond to various stimuli, such as temperature, pH, light, magnetic fields, and biochemical signals. Furthermore, their biocompatibility and capacity to acclimate to many biological conditions make them appropriate for sophisticated applications, including gene treatments, tissue regeneration, and cell therapies. Microfluidics has transformed the creation of hydrogel particles, providing precise control over their dimensions, morphology, and stability. This technique facilitates reproducible and highly efficient production, reducing reagent waste and optimizing drug encapsulation. The integration of microfluidics with hydrogels provides opportunities for the advancement of creative and effective solutions in contemporary medicine. Full article

The handling and fluidization of amorphous soft solids, such as emulsions, foams, or gels, is crucial in many technological processes. This is generally achieved by applying mechanical stress that overcomes a critical threshold, known as yield stress, below which these systems behave as elastic solids. However, the interaction with the walls can facilitate the transition from solid to fluid by activating rearrangements of the fluid constituents close to the wall, resulting in increased fluidity of the system up to distances greater than the spatial scale of the rearrangements. We address the impact of wedge-shaped microroughness on activating the fluidization of emulsion droplets in pressure-driven flow through microfluidic channels. We realize the micro wedges by maskless photolithography to texture one wall of the channel and measure the velocity profiles for flow directed accordingly and against the increasing ramp of the wedge-shaped grooves. We report the enhancement of the emulsion flow in the direction of the climbing ramp of the wedge activated by increasing the magnitude of the pressure gradient. A gain for the volumetric flow rate is registered with respect to the opposite direction as being to $30\%$, depending on the pressure drop. Full article

In practical applications of droplet actuation using digital microfluidic (DMF) systems based on electrowetting-on-dielectric (EWOD), various electrode failures can still arise due to diverse operational conditions. To improve droplet transport efficiency, this study proposes a heuristic-elite genetic algorithm (HEGA) for droplet path planning. We introduce a heuristic method and a bidirectional elite fragment recombination method to address the challenge of poor initialization quality in genetic algorithms, particularly in complex environments. These approaches aim to enhance the global search capability and accelerate the algorithm’s convergence. Simulations were performed using MATLAB, and the results indicate that compared to the basic ant colony algorithm, the proposed method reduces the average number of turning points by approximately 17.23% and the average search time by about 92.60%. In multi-droplet transport applications, the algorithm generates optimal paths for test droplets while maintaining fast convergence. Additionally, it effectively prevents droplets from accidentally contacting or merging in non-synthesis areas, ensuring improved testing outcomes for the chip. Full article

Microfluidic devices are greatly affected by the materials used. The materials used in previous studies had problems in various aspects, such as processing, adsorption, and price. This study will investigate the materials needed to overcome such problems. Various microfluidic devices based on the perfluorinated compound perfluoropolyether (PFPE) were fabricated and mixed with hydrophilic and amphiphilic monomers, including poly(ethylene glycol) diacrylate, polyethylene glycol monomethacrylate, poly(ethylene glycol) methyl ether methacrylate, acrylic acid, and 2-hydroxyethyl methacrylate. A PFPE-based sheet with a repeating structure of hydrophobic and hydrophilic groups was fabricated. Thus, the hydrophilicity of highly hydrophobic PFPE was enhanced. The fluidic channel was engraved on a PFPE-based sheet using laser cutting and a fabricated microfluidic device. The channels of microfluidic devices are micro-scale (100 µm~300 µm). The lipid nanoparticles and droplets generated through the microfluidic device demonstrated uniform particles continuously. Full article

Step emulsification (SE) is renowned for its robustness in generating monodisperse emulsion droplets at arrayed nozzles. However, few studies have explored poly(dimethylsiloxane) (PDMS)-based SE devices for producing monodisperse oil-in-water (O/W) droplets and polymeric microspheres with diameters below 20 µm—materials with broad applicability. In this study, we present a PDMS-based microfluidic SE device designed to achieve this goal. Two devices with 264 nozzles each were fabricated, featuring straight and triangular nozzle configurations, both with a height of 4 µm and a minimum width of 10 µm. The devices were rendered hydrophilic via oxygen plasma treatment. A photocurable acrylate monomer served as the dispersed phase, while an aqueous polyvinyl alcohol solution acted as the continuous phase. The straight nozzles produced polydisperse droplets with diameters exceeding 30 µm and coefficient-of-variation (CV) values above 10%. In contrast, the triangular nozzles, with an opening width of 38 µm, consistently generated monodisperse droplets with diameters below 20 µm, CVs below 4%, and a maximum throughput of 0.5 mL h⁻¹. Off-chip photopolymerization of these droplets yielded monodisperse acrylic microspheres. The low-cost, disposable, and scalable PDMS-based SE device offers significant potential for applications spanning from laboratory-scale research to industrial-scale particle manufacturing. Full article

Microfluidic devices have revolutionized biosensing by enabling precise manipulation of minute fluid volumes across diverse applications. This review investigates the incorporation of machine learning (ML) into the design, fabrication, and application of microfluidic biosensors, emphasizing how ML algorithms enhance performance by improving design accuracy, operational efficiency, and the management of complex diagnostic datasets. Integrating microfluidics with ML has fostered intelligent systems capable of automating experimental workflows, enabling real-time data analysis, and supporting informed decision-making. Recent advances in health diagnostics, environmental monitoring, and synthetic biology driven by ML are critically examined. This review highlights the transformative potential of ML-enhanced microfluidic systems, offering insights into the future trajectory of this rapidly evolving field. Full article