Microfluidic Research Research Articles

Optimizing Hot Embossing of Poly(methyl methacrylate) Microfluidic Chip

Microfluidic research become a more important research field in mechanical and bioengineering fields. The application of microfluidic positively relates to the ability to manufacture micro or precision. Nowadays, the manufacturing in this area is aimed at around 100-500 µm. Here, a hot embossing method is reported to realize microchannel with height and width dimensions of 150-300 µm and 600-800 µm, respectively. This study also shows that the margin factor between the mould/dies to the realized dimension is 50-70% and 5-7% for height and width, respectively.

Hydrodynamic characteristics of detachment length and flow mapping in T-junction circular microchannel

This study investigates the droplet formation process in T-junction circular microchannels, emphasizing the influence of wetting properties and contact angles under various operating conditions. A coupled Volume-of-Fluid (VOF)/Level-set multiphase model is employed for Computational Fluid Dynamics (CFD) simulations to accurately capture the microscale phenomena. The effects of contact angles ranging from 125° to 145°, two-phase flow velocities (0.04–0.25 m/s), and interfacial tension (0.035–0.055 N/m) are systematically analyzed. The findings reveal that these parameters significantly impact the detachment length and flow patterns, with four distinct flow regimes identified: dripping, slug, jetting, and annular flow. New dimensionless correlations for slug and detachment lengths are developed and validated through experimental data, offering improved predictive capabilities. The comprehensive flow mapping provided in this study enhances the understanding of multiphase flows in microchannels, offering valuable insights for the optimization of microfluidic device design and practical applications such as extractive desulphurization. These contributions present a novel approach to integrating contact angle effects into microfluidic research, addressing previously overlooked aspects and providing robust guidelines for future studies.

A Synergistic Overview between Microfluidics and Numerical Research for Vascular Flow and Pathological Investigations.

Vascular diseases are widespread, and sometimes such life-threatening medical disorders cause abnormal blood flow, blood particle damage, changes to flow dynamics, restricted blood flow, and other adverse effects. The study of vascular flow is crucial in clinical practice because it can shed light on the causes of stenosis, aneurysm, blood cancer, and many other such diseases, and guide the development of novel treatments and interventions. Microfluidics and computational fluid dynamics (CFDs) are two of the most promising new tools for investigating these phenomena. When compared to conventional experimental methods, microfluidics offers many benefits, including lower costs, smaller sample quantities, and increased control over fluid flow and parameters. In this paper, we address the strengths and weaknesses of computational and experimental approaches utilizing microfluidic devices to investigate the rheological properties of blood, the forces of action causing diseases related to cardiology, provide an overview of the models and methodologies of experiments, and the fabrication of devices utilized in these types of research, and portray the results achieved and their applications. We also discuss how these results can inform clinical practice and where future research should go. Overall, it provides insights into why a combination of both CFDs, and experimental methods can give even more detailed information on disease mechanisms recreated on a microfluidic platform, replicating the original biological system and aiding in developing the device or chip itself.

Magnetically-responsive microwall arrays with path-guide for directional transportation of droplets

This research provides a comprehensive exploration of the development and characterization of magnetically responsive microwall arrays (MRMAs), presenting a novel approach to precise droplet manipulation. The proposed fabrication process involves microscale wall arrays created using carbonyl iron particles embedded in polydimethylsiloxane through a replica molding process. The MRMAs demonstrate a unique response to magnetic fields, enabling precise control over droplet movement. Through superhydrophobic coatings and meticulously adjusted magnetic fields, the system facilitates the efficient movement of droplets along predefined routes, achieving outstanding accuracy in droplet directionality and positioning. The experiments highlight the capability of MRMAs to merge differently colored droplets, underscoring their potential in long-distance droplet transportation. The results suggest applications in microfluidic systems, lab-on-a-chip devices, and targeted drug delivery, marking a significant advancement in microfluidic research.

Study on the Cleanup Mechanism of Microemulsion Acid Based on Microfluidic Experiment

Summary During an acid fracturing treatment, the preflush and spent acid injected by multistage alternate injection will enter the matrix; this part of the aqueous phase entering the matrix will cause serious water blocking damage during crude oil production, hinder the migration of crude oil in the matrix, and reduce the well productivity. There is a large amount of small-sized pore throats in low-permeability bioclastic limestone reservoirs. The small-sized pore throats are important channels for hydrocarbon flow and are more vulnerable to water blocking under the effect of capillary pressure. The multistage alternating injection of microemulsion acid is a key technology to unlock the commercial potential of low-permeability porous limestone reservoirs, which has the advantages of high acid conductivity, long action distance, less solid residue, and low water blocking damage. This technology has demonstrated good usability in field tests, and the relevant laboratory studies mainly focus on understanding the stimulation effect of microemulsion acid through macroscopic core experiments. But there is still no clear explanation at the microscopic level for why this system can expand its invasion range and mitigate the water blocking damage. To evaluate the effect of microemulsion acid in limestone reservoirs and provide a reference for its application, the properties and mechanism of this system are studied in this paper, while the systems commonly used in the acid pressing process (spent acid without cleanup additive, spent acid added with cleanup additive, and spent emulsified acid) are selected as the control group. According to the characteristics of multimode pore throat in limestone reservoir, a special micromodel with CaCO3 coating is developed. The microfluidic research is carried out to visually present the dynamics of multiphase flow during different spent acids invasion and flowback processes. The cleanup mechanism of microemulsion acid was revealed, while highlighting its application advantages through comparative analysis.

Visualization and Analysis of Mapping Knowledge Domain of Fluid Flow Related to Microfluidic Chip.

Microfluidic chips are important tools to study the microscopic flow of fluid. To better understand the research clues and development trends related to microfluidic chips, a bibliometric analysis of microfluidic chips was conducted based on 1115 paper records retrieved from the Web of Science Core Collection database. CiteSpace and VOSviewer software were used to analyze the distribution of annual paper quantity, country/region distribution, subject distribution, institution distribution, major source journals distribution, highly cited papers, coauthor cooperation relationship, research knowledge domain, research focuses, and research frontiers, and a knowledge domain map was drawn. The results show that the number of papers published on microfluidic chips increased from 2010 to 2023, among which China, the United States, Iran, Canada, and Japan were the most active countries in this field. The United States was the most influential country. Nanoscience, energy, and chemical industry and multidisciplinary materials science were the main fields of microfluidic chip research. Lab on a Chip, Microfluidics and Nanofluidics, and Journal of Petroleum Science and Engineering were the main sources of papers published. The fabrication of chips, as well as their applications in porous media flow and multiphase flow, is the main knowledge domain of microfluidic chips. Micromodeling, fluid displacement, wettability, and multiphase flow are the research focuses in this field currently. The research frontiers in this field are enhanced oil recovery, interfacial tension, and stability.

Evolution of 3d printing technology in fabrication of microfluidic devices and biological applications: a comprehensive review

Lab-on-a-chip or LOC is a term that is used to describe microfluidic devices that integrate multiple analyte detection, which are normally carried out in a laboratory, into one micro-chip unit and may have applications in diverse fields such as electronics, medicine and biomedical domains. Even though microfluidics has advanced greatly during the past decade due to increased needs for portability, reduced sample requirement and multiple analyte detection capabilities biological research has not adopted the technology at the required pace. This may be owing to the time-consuming and expensive process involved in the microfabrication of biochips, the requirement of specialised setup facilities and the extremely high cost associated with microfluidics as compared to conventional technologies. In recent years, three-dimensional (3D) printing has piqued curiosity in the scientific community. It has the potential to create complex, high-resolution structures and that too in a short timeframe depending upon device complexity. This could inspire progressive research in microfluidics, particularly finding applications in biomedical engineering and point-of-care diagnostics. This article gives an overview of how 3D printing aids in the manufacture of microfluidic devices for biological applications, as well as the existing 3D printing methods which are utilised for fabrication and the future perspective in the development of microfluidic devices.

Characterizing the Janus colloidal particles in AC electric field and a step towards label-free cargo manipulation

In recent years, researchers have been exploring Janus particles, a unique type of colloidal system, which has gained enormous attention across diverse fields, from soft matter physics to biology. These particles, possessing an asymmetric surface, can be manipulated in the fluid using external energy sources. This versatility makes them suitable for mimicking biological systems and applications like cargo transportation, drug delivery, biosensing, and environmental cleanup. The study focuses on the response of metal-dielectric (Ti-PMMA) Janus spheres in the AC field, created through the Physical Vapor Deposition (PVD) technique. When subjected to a uniform AC electric field, these particles exhibit different dynamic behaviors at various frequency ranges. The particles show diverse responses from induced-charge electrophoresis (ICEP: 500 Hz-80 kHz) to reversed motion (r: ICEP:100 kHz-1 MHz) and linear chain formation (1 MHz). Additionally, they randomly cluster near the lower characteristic frequency (800 Hz) of the ICEP, whereas they exhibit the 3D motion at frequencies (100 Hz) below this lower characteristic value. The mechanisms behind these dynamic phenomena could be explained by considering the concept of electric double layer (EDL), self-dielectrophoresis (sDEP), dipolar interactions, hydrodynamic interactions, and electrothermal effects. These active Janus Colloids are further leveraged to manipulate 1 µm diameter PMMA passive microparticles and E. coli bacteria at 1 kHz, showcasing their potential applications in cargo delivery under various microfluidic research areas. The manipulation of payloads could be explained based on dielectrophoretic trapping due to locally generated field gradients around the surface of the Janus sphere. Therefore, the present work offers an unprecedented opportunity to study such out-of-equilibrium complex active matter systems and create novel functional materials. Moreover, it could also be extended as a fuel-free microrobotics system for various biomedical applications such as sensing and on-demand drug or cargo delivery inside the microfluidics chamber.

Accelerating the development of inertial microfluidic devices using numerical modelling and machine learning

Inertial microfluidics allows for passive, label-free manipulation of particles suspended in a fluid. Physical experiments can understand the underlying mechanisms to an extent whereby inertial microfluidic devices are used in real-world applications such as disease diagnostics. However, design processes are often iterative and device optimisation can be improved. Numerical modelling has complementary capabilities to physical experiments, with access to full flow field data and control of design parameters. Numerical modelling is used to uncover the fundamental mechanisms in inertial microfluidics and provides evidence for physical experiments. In recent years, numerical modelling has been increasingly coupled to machine learning algorithms to uncover additional physics and provide fast solutions. In this perspective, I discuss the role numerical modelling will play in future inertial microfluidic device research and the opportunities to combine numerical modelling with machine learning algorithms. Two key areas for future research applying machine learning are highlighted; fast predictions of flow fields and the optimisation of design parameters. Developments in these areas would significantly reduce the resources required in device design and have the potential to uncover new applications.

Physics-informed neural network for solving Young–Laplace equation and identifying parameters

Capillarity is prevalent in nature, daily life, and industrial processes, governed by the fundamental Young–Laplace equation. Solving this equation not only deepens our understanding of natural phenomena but also yields insight into industrial advancements. To tackle the challenges posed by traditional numerical methods in parameter identification and complex boundary condition handling, the Young–Laplace physics-informed neural network (Y–L PINN) is established to solve the Young–Laplace equation within tubular domain. The computations on the classical capillary rise scenario confirm the accuracy of the proposed method on the basis of the comparison with Jurin's law, experimental data, and numerical results. Furthermore, the Y–L PINN method excels in parameter identification, e.g., contact angle, Bond number, and so on. These numerical examples even demonstrate its excellent predictive ability from the noisy data. For the complex boundary, it is rather convenient to obtain the liquid meniscus shapes in vessels, which is in good agreement with the experimental results. We further examine the variation of meniscus profile with wetting condition or discontinuous boundary. Importantly, the Y–L PINN method could directly solve the Young–Laplace equation with discontinuous wetting boundary without additional techniques. This work provides valuable insight for material wettability assessments, microstructure preparation, and microfluidics research.

Realizing the multifunctional microfluidic flow manipulation based on hydrodynamic metamaterials

From their initial application to the fields of chemistry and biology, microfluidic chips used as micro total analysis systems have developed into new technologies to satisfy the requirements of various societal industries. Microchannels are essential components of microfluidic chips; they play a vital role in connecting the inlet and outlet as well as determining the flow distribution and reagent mixing. Microfluidic research has always been devoted to minimizing energy dissipation, fluid resistance, and pressure drop to realize energy-efficient microfluidic chips. This study proposes a new theory for manipulating the flow in microchannels based on hydrodynamic metamaterials according to the spatial transformation theory. In particular, hydrodynamic metamaterials are specifically designed to construct flow shifters, flow splitters, and flow combiners, and theoretical and numerical simulations are performed to assess their hydrodynamic performance. The systematic design of hydrodynamic metamaterial devices proposed in this work establishes a theoretical framework to achieve a steady flow state without inducing unstable flow disturbances in complex-shape microchannels.

Latest Trends In 3D Printed Microfluidics

Over the last decade, there has been a large interest in the use of 3D printing to manufacture microfluidic devices, since it has the ability to circumvent traditional fabrication techniques limitations. These include being unable to really make complex three-dimensional architectures, expensive and time-consuming processes to change device designs, and difficulty transitioning from prototyping to mass production. In this literature review, we will look at the current trends in 3D printed microfluidics, as well as recent advances and new developments in fabrication techniques, materials, and applications. Integration of 3D printing in microfluidics research has helped in the rapid prototyping of fluidic channels and structures with high complexity at an effective cost. Applications of 3D printed microfluidics are described in the areas of healthcare, diagnostics, chemical synthesis, and biotechnology. This paper also delineates the challenges and future prospects of 3D printed microfluidics, giving insight into potential research directions and technological developments.

Nanoparticle manipulation based on chiral plasmon effects.

Chiral plasmonic structures have garnered increasing attention owing to their distinctive chiroptical response. Localized surface plasmon resonance can significantly enhance the circular dichroism and local electromagnetic field of chiral plasmonic structures, resulting in enhanced electromagnetic forces acting on surrounding nanoparticles. Moreover, the circular dichroism response of chiral structures provides an effective means for macroscopic adjustment of microscopic electromagnetic fields. However, chiral plasmon effects are naturally related to angular momentum, and particle control studies of chirality usually focus on angular momentum. This paper proposes a particle manipulation method utilizing chiral light-matter interactions. Through optimization of the optical response of the chiral structure, the direction of electromagnetic forces exerted on surrounding polystyrene particles reverses upon a change in the incident light's handedness. According to this characteristic, the movement direction control of polystyrene particles with a diameter of 100 nm was achieved. By altering the handedness of a single circularly polarized light, more than 94% high-precision particle manipulation was achieved, reducing the complexity of particle manipulation. This microfluidic method has significant implications for advancing microfluidic research and chiral applications.

The egg-counter: a novel microfluidic platform for characterization of Caenorhabditis elegans egg-laying.

Reproduction is a fundamental process that shapes the demography of every living organism yet is often difficult to assess with high precision in animals that produce large numbers of offspring. Here, we present a novel microfluidic research platform for studying Caenorhabditis elegans' egg-laying. The platform provides higher throughput than traditional solid-media behavioral assays while providing a very high degree of temporal resolution. Additionally, the environmental control enabled by microfluidic animal husbandry allows for experimental perturbations difficult to achieve with solid-media assays. We demonstrate the platform's utility by characterizing C. elegans egg-laying behavior at two commonly used temperatures, 15 and 20 °C. As expected, we observed a delayed onset of egg-laying at 15 °C degrees, consistent with published temperature effects on development rate. Additionally, as seen in solid media studies, egg laying output was higher under the canonical 20 °C conditions. While we validated the Egg-Counter with a study of temperature effects in wild-type animals, the platform is highly adaptable to any nematode egg-laying research where throughput or environmental control needs to be maximized without sacrificing temporal resolution.

Surface-Wetting Characteristics of DLP-Based 3D Printing Outcomes under Various Printing Conditions for Microfluidic Device Fabrication.

In recent times, the utilization of three-dimensional (3D) printing technology, particularly a variant using digital light processing (DLP), has gained increasing fascination in the realm of microfluidic research because it has proven advantageous and expedient for constructing microscale 3D structures. The surface wetting characteristics (e.g., contact angle and contact angle hysteresis) of 3D-printed microstructures are crucial factors influencing the operational effectiveness of 3D-printed microfluidic devices. Therefore, this study systematically examines the surface wetting characteristics of DLP-based 3D printing objects, focusing on various printing conditions such as lamination (or layer) thickness and direction. We preferentially examine the impact of lamination thickness on the surface roughness of 3D-printed structures through a quantitative assessment using a confocal laser scanning microscope. The influence of lamination thicknesses and lamination direction on the contact angle and contact angle hysteresis of both aqueous and oil droplets on the surfaces of 3D-printed outputs is then quantified. Finally, the performance of a DLP 3D-printed microfluidic device under various printing conditions is assessed. Current research indicates a connection between printing parameters, surface roughness, wetting properties, and capillary movement in 3D-printed microchannels. This correlation will greatly aid in the progress of microfluidic devices produced using DLP-based 3D printing technology.

Micromixing within microfluidic devices: Fundamentals, design, and fabrication

As one of the hot spots in the field of microfluidic chip research, micromixers have been widely used in chemistry, biology, and medicine due to their small size, fast response time, and low reagent consumption. However, at low Reynolds numbers, the fluid motion relies mainly on the diffusive motion of molecules under laminar flow conditions. The detrimental effect of laminar flow leads to difficulties in achieving rapid and efficient mixing of fluids in microchannels. Therefore, it is necessary to enhance fluid mixing by employing some external means. In this paper, the classification and mixing principles of passive (T-type, Y-type, obstructed, serpentine, three-dimensional) and active (acoustic, electric, pressure, thermal, magnetic field) micromixers are reviewed based on the presence or absence of external forces in the micromixers, and some experiments and applications of each type of micromixer are briefly discussed. Finally, the future development trends of micromixers are summarized.

Inexpensive and rapid fabrication of PDMS microfluidic devices for biological testing applications using low cost commercially available 3D printers

Polydimethylsiloxane (PDMS) elastomers have been extensively used in the development of microfluidic devices, capable of miniaturizing biomolecular and cellular assays to the microlitre and nanolitre range, thereby increasing the throughput of experimentation. PDMS has been widely used due to its optical clarity and biocompatibility, among other desirable physical and chemical properties. Despite the widespread use of PDMS in microfluidic devices, the fabrication process typically via soft lithography technology requires specialized facilities, instruments, and materials only available in a limited number of laboratories. To expand microfluidic research capabilities to a greater scientific population, we developed and characterized a simple and robust method of fabricating relatively inexpensive PDMS microfluidic devices using readily available reagents and commercially available three-dimensional (3D) printers. The moulds produced from the 3D printers resolve designed microfluidic channel features accurately with high resolution (>100 µm). The critical physical and chemical post-processing modifications we outline here are required to generate functional and optically clear microfluidic devices.

Accelerating intelligent microfluidic image processing with transfer deep learning: A microchannel droplet/bubble breakup case study

Deep learning has recently been leveraged in the microfluidic research for intelligent image processing. However, it usually requires massive human efforts to label sufficient images for obtaining a precise deep learning model. We herein propose an integrated microfluidic image processing method based on transfer deep learning for the rapid deployment of Mask R-CNN, which is capable of reutilizing models trained in previous microfluidic domains to accelerate the analysis of droplets and bubbles in the images of the target microfluidic domain. The transfer deep learning is validated in the microfluidic research with a constrictive microchannel, which is commonly used to break large droplets or bubbles to enhance emulsification. With only 40 labeled images and about 10 min training, the integrated image processing method achieves precise recognition results for both droplets and bubbles in the microfluidic experiments. Applying the trained Mask R-CNN to unlabeled images, the breakup of droplets is found to be highly dependent on the low flow rate, but the bubble breakup is much easier to happen in the same microfluidic equipment. Critical conditions of droplet breakup and size laws of droplet and bubble are precisely determined based on the recognition results of the trained Mask R-CNN.

Developments and Applications of Microfluidic Pumps and Valves

Microfluidic technology is used a lot in modern engineering. Microfluidic pumps and valves are key topics of microfluidic research today. Microfluidic pumps and valves have long life of equipment with low power waste. They can transport liquids like water and oil. Microfluidic pumps and valves are widely used in household appliances, cooling systems and medical devices. However, there is still a research gap on the improvement of the performance of the microfluidic pumps and valves. Therefore, this paper summarizes the recent developments and applications of the design and optimization techniques for micropumps and microvalves. The basic principle of topology optimization technique for micro-pumps and valves and its applications are detailed. Research findings are summarized. Suggestions are put forward to provide useful guidelines for future research. Overall, this paper can be served as a useful reference for those who would like to know the optimization design method of microfluidic pumps and valves.

Monolithically 3D-Printed Microfluidics with Embedded µTesla Pump.

Microfluidics has earned a reputation for providing numerous transformative but disconnected devices and techniques. Active research seeks to address this challenge by integrating microfluidic components, including embedded miniature pumps. However, a significant portion of existing microfluidic integration relies on the time-consuming manual fabrication that introduces device variations. We put forward a framework for solving this disconnect by combining new pumping mechanics and 3D printing to demonstrate several novel, integrated and wirelessly driven microfluidics. First, we characterized the simplicity and performance of printed microfluidics with a minimum feature size of 100 µm. Next, we integrated a microtesla (µTesla) pump to provide non-pulsatile flow with reduced shear stress on beta cells cultured on-chip. Lastly, the integration of radio frequency (RF) device and a hobby-grade brushless motor completed a self-enclosed platform that can be remotely controlled without wires. Our study shows how new physics and 3D printing approaches not only provide better integration but also enable novel cell-based studies to advance microfluidic research.