Microscale Channels Research Articles

Neural network-enabled, all-electronic control of non-Newtonian fluid flow.

Real-time, all-electronic control of non-Newtonian fluid flow through a microscale channel is crucial for various applications in manufacturing and healthcare. However, existing methods lack the sensitivity required for accurate measurement and the real-time responsiveness necessary for effective adjustment. Here, we demonstrate an all-electronic system that enables closed-loop, real-time, high-sensitivity control of various waveforms of non-Newtonian fluid flow (0.76 μl min-1) through a micro-sized outlet. Our approach combines a contactless, cuff-like flow sensor with a neural-network control program. This system offers a simple, miniaturized, versatile, yet high-performance solution for non-Newtonian fluid flow control, easily integrated into existing setups.

Study of the Flow Characteristics of Pumped Media in the Confined Morphology of a Ferrofluid Pump With Annular Microscale Constraints

Abstract The driving mechanism of ferrofluid micropumps under the constraints of an annular microscale morphology is not fully understood. The gap between microfabrication technology and the fundamental theory of microfluidics has become a substantial obstacle to the development and application of ferrofluid micropumps. In this study, we first theoretically analyzed the Knudsen numbers of millimeter-scale microfluids using Jacobson's molecular hard sphere model, obtaining the initial conclusion that liquid flow conforms to the continuum hypothesis in geometric morphologies with characteristic dimensions greater than 7 × 10−8 m. Subsequently, using a microscopic lens combined with the particle image velocimetry optical measurement method, the flow patterns in millimeter-scale annular flow channels were captured and we observed wall slip phenomena in which the slip length of the millimeter-scale channel approached the micron level. The slip velocity and flowrate through the cross section of the microscale channel followed a logarithmic function relationship and could be divided into rapid growth, slow growth, and stable stages. As the characteristic scale of the channel was further reduced, the linear relationship between the slip velocity and cross-sectional flowrate in the rapid growth stage was broken, and the nonlinear relationship approximated an exponential function. Finally, a theoretical model for the flow behavior of the driving fluid in a ferrofluid micropump was established using slip boundary conditions. The flow patterns in microscale ring flow under slip conditions conformed to a quadratic function.

Periodic Flows in Microfluidics.

Microfluidics, the science and technology of manipulating fluids in microscale channels, offers numerous advantages, such as low energy consumption, compact device size, precise control, fast reaction, and enhanced portability. These benefits have led to applications in biomedical assays, disease diagnostics, drug discovery, neuroscience, and so on. Fluid flow within microfluidic channels is typically in the laminar flow region, which is characterized by low Reynolds numbers but brings the challenge of efficient mixing of fluids. Periodic flows are time-dependent fluid flows, featuring repetitive patterns that can significantly improve fluid mixing and extend the effective length of microchannels for submicron and nanoparticle manipulation. Besides, periodic flow is crucial in organ-on-a-chip (OoC) for accurately modeling physiological processes, advancing disease understanding, drug development, and personalized medicine. Various techniques for generating periodic flows have been reported, including syringe pumps, peristalsis, and actuation based on electric, magnetic, acoustic, mechanical, pneumatic, and fluidic forces, yet comprehensive reviews on this topic remain limited. This paper aims to provide a comprehensive review of periodic flows in microfluidics, from fundamental mechanisms to generation techniques and applications. The challenges and future perspectives are also discussed to exploit the potential of periodic flows in microfluidics.

Microscale channels produced by micro friction stir channeling (μFSC)

The current literature lacks comprehensive research on the processing limits of the Friction Stir Channeling process (FSC) for creating the smallest continuous and integral channels, using tools with threaded probes 2 mm in diameter or smaller. This study pioneers the exploration of the extreme limits of the microscale FSC process, with potential applications in the development of ultra-compact heat exchangers, seeking to enhance the efficiency and sustainability of these systems. Customized tools were designed and manufactured, with predefined dimensions and geometries to establish a set of parameters that consistently produce continuous microchannels, maximizing the hydraulic diameter within the constraints of each tool's specifications and geometry. Comprehensive evaluations—including continuity, watertightness, micro-computed tomography, neutron computed tomography, microhardness testing, and thermal measurements—were conducted to ensure the channels' structural integrity and suitability for super-compact heating and cooling applications. Internal channels were successfully created using tools with threaded probes measuring 2.0, 1.0, and 0.5 mm in diameter, and corresponding shoulder diameters of 5, 4, and 3.5 mm, within 5 mm thick AW1050-H111 aluminum alloy plates. The smallest channel achieved a hydraulic diameter of 191 μm, using a 0.5 mm diameter threaded probe, thus qualifying it as a microchannel. The thermal performance of a compact heat exchanger model was also tested, demonstrating that despite the high cost associated with tool production, particularly due to the specialized manufacturing processes required, the FSC process remains viable, reliable, and repeatable for the production of mini- and micro-channels.

Organic synaptic transistor showing ultralow energy consumption with a microscale channel by laser ablation

Low energy consumption per synaptic event is important for artificial synapses in applications of highly integrated and large-scale neuromorphic computing systems. Reducing the channel length of a synaptic transistor is an effective method to achieve this goal because such devices can work under low operating voltage and current. In this Letter, we use femtosecond laser ablation to fabricate a microscale slit in an Ag film as the channel of an organic synaptic transistor to obtain low energy consumption. The length of the shortest channel is only 1.6 μm. As a result, the device could be driven by a 50 μV drain bias voltage while output 855 pA excitatory postsynaptic current under a gate spike of 50 mV and 30 ms. The calculated energy consumption per synaptic event is 1.28 fJ, which is comparable to that of a biological synapse (1–10 fJ per synaptic event). Femtosecond laser ablation has been demonstrated a rapid and effective process for the fabrication of microscale channel with high resolution for synaptic transistor, showing large potential for the development of neuromorphic electronics.

Acoustofluidics-enhanced biosensing with simultaneously high sensitivity and speed

Simultaneously achieving high sensitivity and detection speed with traditional solid-state biosensors is usually limited since the target molecules must passively diffuse to the sensor surface before they can be detected. Microfluidic techniques have been applied to shorten the diffusion time by continuously moving molecules through the biosensing regions. However, the binding efficiencies of the biomolecules are still limited by the inherent laminar flow inside microscale channels. In this study, focused traveling surface acoustic waves were directed into an acoustic microfluidic chip, which could continuously enrich the target molecules into a constriction zone for immediate detection of the immune reactions, thus significantly improving the detection sensitivity and speed. To demonstrate the enhancement of biosensing, we first developed an acoustic microfluidic chip integrated with a focused interdigital transducer; this transducer had the ability to capture more than 91% of passed microbeads. Subsequently, polystyrene microbeads were pre-captured with human IgG molecules at different concentrations and loaded for detection on the chip. As representative results, ~0.63, 2.62, 11.78, and 19.75 seconds were needed to accumulate significant numbers of microbeads pre-captured with human IgG molecules at concentrations of 100, 10, 1, and 0.1 ng/mL (~0.7 pM), respectively; this process was faster than the other methods at the hour level and more sensitive than the other methods at the nanomolar level. Our results indicated that the proposed method could significantly improve both the sensitivity and speed, revealing the importance of selective enrichment strategies for rapid biosensing of rare molecules.

Role of graphene oxide infusion in concrete to elevate strength and fire performance in construction concrete

The study is centered on optimizing graphene oxide (GO) concentration in M30 designer mix concrete, aiming to enhance its performance under elevated temperatures and fire conditions. The findings revealed a significant 40 % increase in compressive strength with the addition of 0.05 wt% GO to M30 grade concrete after 28 days of curing in water. GO played a crucial role in mitigating the impact of high temperatures under heating in furnace and fire exposure under flame, resulting in reduced crack formation and a delayed temperature rise during thermal loading. In heat resistance assessments, GO concrete exhibited a substantial delay in temperature rise compared to plain concrete under controlled furnace conditions, showcasing superior resistance to elevated temperatures. Thermogravimetric analysis and Differential TG analysis elucidated the superior retention of water and hydrated products in GO concrete, even after exposure to high temperatures. Fire exposure tests demonstrated that GO concrete exhibited a much lower surface temperature (less than 50 °C) opposite to the flame (flame temperature ∼ 700 °C) within a 15 cm width of concrete. Additionally, fewer and less severe cracks appeared in the GO concrete compared to plain concrete, showcasing its anti-spalling behavior. The altered matrix porosity of GO concrete, creating nano- and microscale channels, contributed to reduced vapor pressure and mitigated crack formation. This comprehensive study underscores the potential of GO as a versatile additive in concrete, offering enhancements in strength, heat resistance, and fire performance for sustainable and resilient infrastructure development.

Degradation of superhydrophobic aluminium overhead line conductor surfaces

AbstractIt has been shown that noise emissions from HV overhead line conductors can be reduced under rain conditions by making their surfaces superhydrophobic. The working environment makes ensuring the longevity of any treatment a major challenge. The degradation of various superhydrophobic surfaces generated by applying a superhydrophobic coating and patterning microscale channels is assessed under an AC electric field (18 kV/cm) with continuous water spray. By examining the droplet distribution on the surfaces during the degradation and the surface roughness before and after degradation, the authors demonstrate that no water droplets were found on the microscale patterned surface, but droplets were formed on the coated surface after degradation. The surface roughness reduction of the coated surface and microscale patterned surface was 29.8% and 11.3%, respectively, indicating that the microscale patterned surface has better durability than the superhydrophobic coating under the AC electric stress.

Advancement in Generation and Application of Microfluidic Chip Technology

Microfluidics is an interdisciplinary topic of research that draws inspiration from other areas such as fluid dynamics, microelectronics, materials science, and physics. Microfluidics has made it possible to create microscale channels and chambers out of a broad variety of materials by borrowing ideas from a number of different fields. This has opened up exciting possibilities for the development of platforms of any size, shape, and geometry using a variety of approaches. One of the most significant advantages of microfluidics is its versatility in applications. Microfluidic chips can be used for a variety of purposes, such as incorporating nanoparticles, encapsulating and delivering drugs, targeting cells, analyzing cells, performing diagnostic tests, and cultivating cells. This adaptability has led to the development of several device-like systems for use in a range of settings. In this study, we explore cutting-edge novel applications for microfluidic and nanofabrication technologies. We examine current developments in the area of microfluidics and highlight their potential for usage in the medical industry. We pay special attention to digital microfluidics, a recently developed and very useful technique for illness diagnosis and monitoring. The originality of microfluidics is found in the fact that it allows for the miniaturization of complex systems and processes, paving the way for the creation of cutting-edge gadgets with wide-ranging practical applications. Microfluidics has the potential to transform various fields, including medicine, biotechnology, environmental monitoring, and more. The development of novel microfluidic platforms, coupled with advancements in digital microfluidics, promises to revolutionize the way we diagnose, treat, and monitor diseases.

Microscale advection governs microbial growth and oxygen consumption in macroporous aggregates.

Most microbial life on Earth is found in localized microenvironments that collectively exert a crucial role in maintaining ecosystem health and influencing global biogeochemical cycles. In many habitats such as biofilms in aquatic systems, bacterial flocs in activated sludge, periphyton mats, or particles sinking in the ocean, these microenvironments experience sporadic or continuous flow. Depending on their microscale structure, pores and channels through the microenvironments permit localized flow that shifts the relative importance of diffusive and advective mass transport. How this flow alters nutrient supply, facilitates waste removal, drives the emergence of different microbial niches, and impacts the overall function of the microenvironments remains unclear. Here, we quantify how pores through microenvironments that permit flow can elevate nutrient supply to the resident bacterial community using a microfluidic experimental system and gain further insights from coupled population-based and computational fluid dynamics simulations. We find that the microscale structure determines the relative contribution of advection vs diffusion, and even a modest flow through a pore in the range of 10 µm s-1 can increase the carrying capacity of a microenvironment by 10%. Recognizing the fundamental role that microbial hotspots play in the Earth system, developing frameworks that predict how their heterogeneous morphology and potential interstitial flows change microbial function and collectively alter global scale fluxes is critical.IMPORTANCEMicrobial life is a key driver of global biogeochemical cycles. Similar to the distribution of humans on Earth, they are often not homogeneously distributed in nature but occur in dense clusters that resemble microbial cities. Within and around these clusters, diffusion is often assumed as the sole mass-transfer process that dictates nutrient supply and waste removal. In many natural and engineered systems such as biofilms in aquatic environments, aggregates in bioremediation, or flocs in wastewater treatment plants, these clusters are exposed to flow that elevates mass transfer, a process that is often overlooked. In this study, we show that advective fluxes can increase the local growth of bacteria in a single microenvironment by up to 50% and shape their metabolism by disrupting localized anoxia or supplying nutrients at different rates. Collectively, advection-enhanced mass transport may thus regulate important biogeochemical transformations in both natural and engineered environments.

Optimizing the methodology for accurate and accessible slip length measurement with atomic force microscopy

The remarkable performance of cooling devices employing nano- and microscale channels has drawn considerable interest, highlighting the need for surfaces with large slip lengths to improve their efficiency. However, the large errors in slip length associated with existing techniques hinder a clear understanding of slip phenomena. In this paper, we evaluate existing analytical methods for slip length measurement with atomic force microscopy (AFM) and propose a new reliable method. We performed force curve measurements on mica, silica and highly ordered pyrolytic graphite surfaces in water using an AFM equipped with a colloidal probe. The obtained force curves were analyzed through three methods: two commonly utilized procedures, namely the recursive and intercept methods, and a novel one called the two-parameter method which we developed. Our analyses showed that the recursive method yielded slip lengths with relatively large errors, fluctuation of ±5.8 nm, which were due to inaccuracies in the cantilever's spring constant and the fluid viscosity. On the other hand, it was found that the intercept method leads to restrictions on the choice of fitting range because of the simplified formula for viscous drag. As a result, by altering the data range, the calculated slip length shows significant variations within the ranges of ±27.5 nm. The two-parameter method, unlike the standard ones, overcome these drawbacks. This method requires no pre-measured parameters, and the slip length fluctuation is independent of the fitting range and only ±3.6 nm, which is around 2/3 of that observed in the recursive method and 1/8 of that in the intercept method. Our study optimizes existing analytical protocols and offers a new way for accessible and reliable calculations of slip lengths.

Turbulence models performance to predict fluid mechanics and heat transfer characteristics of fluids flow in micro-scale channels

The predictability of the mathematical models on the details and the phenomenology for microscale flow conditions is an open topic in the literature. In this sense, this work evaluates the capacity of the following turbulence models: standard k − ε , RNG k − ε , k − ω standard, k − ω SST , Realizable k − ε , and Low-Re k − ε to predict the fluid mechanics and heat transfer characteristics of low Global Warming Potential (GWP) fluid flow in a 1.1 mm ID microchannel. These turbulence models are evaluated for Reynolds Numbers up to 104. The numerical results for velocity profile, friction factors, and Nusselt Numbers are validated with analytical and experimental data published in previous works for R134a, R1234yf, R1234ze(E), and R600a. Parametric behaviors of pressure drop and heat transfer coefficient are presented and analyzed. The results indicate that each of the models describes the qualitative behavior of flow and heat transfer processes. On the other hand, the quantitative results indicate that the Low-Re k − ε , k − ω , and k − ω SST models demonstrate an acceptable prediction of some variable’s behavior. Numerically, the Low-Re k − ε model presents an accurate prediction with the lowest mean absolute.

A liquid–metal-based microscale calorimetric in-chip flow sensor for flow rate measuring

Abstract This work proposes a liquid–metal-based calorimetric micro-flow sensor within a polydimethylsiloxane (PDMS) chip. It can measure the flow rate of fluid in microscale channels, with a range as low as several microliters per minute. This in-chip sensor is proposed to solve the issue of detecting the flow rate in microfluidic systems. To make the sensor compatible with PDMS microfluidic chips, low-melting-point gallium-based alloy and bismuth-based (bi-based) alloy are used to make the micro heater and bi-metal thermocouples, for these alloys can be easily injected into a PDMS chip to form electrodes. To minimize heat resistance (or temperature difference) between fluid and the detecting ends of thermocouples, these ends are directly exposed to liquid in the flow channel with the help of a special reversible bonding technology. Thermocouples are connected in series to improve the sensor’s response. A novel method to bond and electrically connect the sensor to a print circuit board is also elaborated. Since the calorimetric flow sensor is sensitive to heating power, fluid temperature and environment cooling, a dimensionless parameter less independent of these factors is deduced from heat transfer theory, and this idea is used in result processing to offset the bad effect. Experiments with pure water show that this sensor can be used to detect flow rates, with a resolution up to 4 µl min−1 mV−1 and a range of 12 µl min−1 in this case, and that at different heating powers, the thermal potential results vary significantly whereas the dimensionless results nearly keep the same. Present work indicates that this sensor has the potential to be integrated into a PDMS microfluidic system and to provide accurate and stable results if a dimensionless method is used in data processing.

Analyzing the effects of helical flow in blood vessels using acoustofluidic-based dynamic flow generator

The effects of helical flow in a blood vessel are investigated in a dynamic flow generator using surface acoustic wave (SAW) in the microfluidic device. The SAW, generated by an interdigital transducer (IDT), induces acoustic streaming, resulting in a stable and consistent helical flow pattern in microscale channels. This approach allows rapid development of helical flow within the channel without directly contacting the medium. The precise design of the window enables the creation of distinct unidirectional vortices, which can be controlled by adjusting the amplitude of the SAW. Within this device, optimal operational parameters of the dynamic flow generator to preserve the integrity of endothelial cells are found, and in such settings, the actin filaments within the cells are aligned to the desired state. Our findings reveal that intracellular Ca2+ concentrations vary in response to flow conditions. Specifically, comparable maximum intensity and graphical patterns were observed between low-flow rate helical flow and high-flow rate Hagen-Poiseuille flow. These suggest that the cells respond to the helical flow through mechanosensitive ion channels. Finally, adherence of monocytes is effectively reduced under helical flow conditions in an inflammatory environment, highlighting the atheroprotective role of helical flow. Statement of SignificanceHelical flow in blood vessels is well known to prevent atherosclerosis. However, despite efforts to replicate helical flow in microscale channels, there is still a lack of in vitro models which can generate helical flow for analyzing its effects on the vascular system. In this study, we developed a method for generating steady and constant helical flow in microfluidic channel using acoustofluidic techniques. By utilizing this dynamic flow generator, we were able to observe the atheroprotective aspects of helical flow in vitro, including the enhancement of calcium ion flux and reduction of monocyte adhesion. This study paves the way for an in vitro model of dynamic cell culture and offers advanced investigation into helical flow in our circulatory system.

Microfluidics in smart food safety.

The evolution of food safety practices is crucial in addressing the challenges posed by a growing global population and increasingly complex food supply chains. Traditional methods are often labor-intensive, time-consuming, and susceptible to human error. This chapter explores the transformative potential of integrating microfluidics into smart food safety protocols. Microfluidics, involving the manipulation of small fluid volumes within microscale channels, offers a sophisticated platform for developing miniaturized devices capable of complex tasks. Combined with sensors, actuators, big data analytics, artificial intelligence, and the Internet of Things, smart microfluidic systems enable real-time data acquisition, analysis, and decision-making. These systems enhance control, automation, and adaptability, making them ideal for detecting contaminants, pathogens, and chemical residues in food products. The chapter covers the fundamentals of microfluidics, its integration with smart technologies, and its applications in food safety, addressing the challenges and future directions in this field.

Neuroinflammatory response on a newly combinatorial cell-cell interaction chip.

Neuroinflammation is a common feature in various neurological disorders. Understanding neuroinflammation and neuro-immune interactions is of significant importance. However, the intercellular interactions in the inflammatory model are intricate. Microfluidic chips, with their complex micrometer-scale structures and real-time observation capabilities, offer unique advantages in tackling these complexities compared to other techniques. In this study, microfluidic chip technology was used to construct a microarray physical barrier structure with 15 μm spacing, providing well-defined cell growth areas and clearly delineated interaction channels. Moreover, an innovative hydrophilic treatment process on the glass surface facilitated long-term co-culture of cells. The developed neuroinflammation model on the chip revealed that SH-SY5Y cytotoxicity was predominantly influenced by co-cultured THP-1 cells. The co-culture model fostered complex interactions that may exacerbate cytotoxicity, including irregular morphological changes of cells, cell viability reduction, THP-1 cell migration, and the release of inflammatory factors. The integration of the combinatorial cell-cell interaction chip not only offers a clear imaging detection platform but also provides diverse data on cell migration distance, migration direction, and migration angle. Furthermore, the designed ample space for cell culture, along with microscale channels with fluid characteristics, allow for the study of inflammatory factor distribution patterns on the chip, offering vital theoretical data on biological relevance that conventional experiments cannot achieve. The fabricated user-friendly, reusable, and durable co-culture chip serves as a valuable in vitro tool, providing an intuitive platform for gaining insights into the complex mechanisms underlying neuroinflammation and other interacting models.

Fast-response fiber organic electrochemical transistor with vertical channel design for electrophysiological monitoring.

Fiber organic electrochemical transistors (OECTs) hold significant promise for in vivo bio-signal amplification due to their minimally invasive and seamless integration with biological tissues. However, their use in monitoring rapid physiological changes, such as electrophysiological signals, has been constrained by slow response time, arising from their extensive channel dimensions. Here, we introduce a novel fiber OECT designed with a micro-scale vertical channel (F-vOECT) that substantially reduces the response time by an order of magnitude to 12 ms and achieves a maximum transconductance of 16 mS at zero gate bias, marking a substantial improvement over previous fiber OECTs. This compact and flexible fiber device demonstrates robust performance under cyclic switching, dynamic deformation and exhibits excellent biocompatibility. When subcutaneously implanted in rats, the F-vOECT enables stable, continuous electrocardiogram monitoring for 7 days, successfully identifying episodes of atrioventricular block. These capabilities illustrate its potential for clinical electrophysiological diagnostics. The design strategy of F-vOECT opens new avenues for developing fast-responsive fiber bioelectronic devices.

Solute Transport in Engineered Living Materials Using Bone‐Inspired Microscale Channel Networks

Solute Transport in Engineered Living Materials Using Bone‐Inspired Microscale Channel Networks

Solute Transport in Engineered Living Materials Using Bone‐Inspired Microscale Channel Networks

Engineered living materials (ELMs) are an emerging class of materials that are synthesized and/or populated by living cells to achieve novel functionalities including self‐healing and sensing. Providing nutrients to living cells within an ELM over prolonged periods remains a major technical challenge that limits the service life of ELMs. Bone maintains living cells for decades by delivering nutrients through a network of nanoscale channels punctuated by microscale pores. Nutrient transfer in bone is enabled by mechanical loading experienced by the material during regular use. Herein, the geometric traits of the network of channels and pores that can be used in ELMs to allow mechanical loading to enable nutrient delivery to resident cell populations are identified in a manner seen in bone. Transport occurs when deformation in the microscale pore network exceeds the volume of the connecting channels. Computational models show that transport is enhanced at greater loading magnitudes and lower loading frequencies. The computational results are confirmed using experiments with microfluidic systems. In the findings, quantitative design principles are provided for channel‐pore networks capable of sustained delivery of nutrients to living cells within materials.

Scalable Ultralight Wood-Inspired Aerogel with Vertically Aligned Micrometer Channels for Highly Efficient Solar Interfacial Desalination.

An ultralight material that simultaneously combines remarkably rapid water transportation, highly efficient photothermal conversion, and excellent thermal insulation is highly desired for solar-driven interfacial desalination but was challenging. In this work, inspired by the unique natural structure of wood, we developed an ultralight aerogel by ice-templated synthesis as an integrated interfacial evaporator for solar-driven water production. The interior features vertically aligned biomimetic microscale channels facilitating rapid transportation of water molecules, while an improved photothermal interface allows high solar absorption and conversion via nonradiative relaxation and molecular vibrations. The biomimetic aerogel is ultralight with a density as low as 0.06 g/cm3, especially its fabrication is size- and shape-programmable as a whole and easily scalable. Additionally, the outstanding thermal insulation of the aerogel focuses heat precisely at the evaporation interface, reducing ineffective heat loss, while the uniformly distributed large-sized channels promote the dynamic convection of high concentration salt ions on the evaporator surface. Consequently, the evaporator shows broadband light absorption of 92.7%, leading to a water evaporation rate reaching 4.55 kg m-2 h-1 under 3 simulated solar irradiations, much higher than that of other reported evaporators with randomly distributed pores. This work provides new insight into advanced hybrid aerogels for highly efficient and durable solar-driven interfacial desalination systems.