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The DEP force is usually calculated from the object's point of view using the interaction of the object's induced dipole moment with the inducing field. Recently, we described the DEP behavior of high- and low-conductive 200-µm 2D spheres in a square 1 × 1-mm chamber with a plane-versus-pointed electrode configuration from the system's point of view. Here we extend our previous considerations to the plane-versus-plane and pointed-versus-pointed electrode configurations. The trajectories of the sphere center and the corresponding DEP forces were calculated from the gradient of the system's overall energy dissipation for given starting points. The dissipation's dependence on the sphere's position in the chamber is described by the numerical "conductance field", which is the DC equivalent of the capacitive charge-work field. While the plane-versus-plane electrode configuration is field-gradient free without an object, the presence of the highly or low-conductive spheres generates structures in the conductance fields, which result in very similar DEP trajectories. For both electrode configurations, the model describes trajectories with multiple endpoints, watersheds, and saddle points, very high attractive and repulsive forces in front of pointed electrodes, and the effect of mirror charges. Because the model accounts for inhomogeneous objectpolarization by inhomogeneous external fields, the approach allows the modeling of the complicated interplay of attractive and repulsive forces near electrode surfaces and chamber edges. Non-reversible DEP forces or asymmetric magnitudes for the highly and low-conductive spheres in large areas of the chamber indicate the presence of higher-order moments, mirror charges, etc. [ABSTRACT FROM AUTHOR]

The majority of in vitro studies focusing upon particle–lung cell interactions use static models at an air–liquid interface (ALI). Advancing the physiological characteristics of such systems allows for closer resemblance of the human lung, in turn promoting 3R strategies. PATROLS (EU Horizon 2020 No. 760813) aimed to use a well-characterised in vitro model of the human alveolar epithelial barrier to determine how fluid-flow dynamics would impact the outputs of the model following particle exposure. Using the QuasiVivoTM (Kirkstall Ltd., York, UK) system, fluid-flow conditions were applied to an A549 + dTHP-1 cell co-culture model cultured at the ALI. DQ12 and TiO2 (JRCNM01005a) were used as model particles to assess the in vitro systems' sensitivity. Using a quasi- and aerosol (VitroCell Cloud12, VitroCell Systems, Waldkirch, Germany) exposure approach, cell cultures were exposed over 24 h at IVIVE concentrations of 1 and 10 (DQ12) and 1.4 and 10.4 (TiO2) µg/cm2, respectively. We compared static and fluid flow conditions after both these exposure methods. The co-culture was subsequently assessed for its viability, membrane integrity and (pro-)inflammatory response (IL-8 and IL-6 production). The results suggested that the addition of fluid flow to this alveolar co-culture model can influence the viability, membrane integrity and inflammatory responses dependent on the particle type and exposure. [ABSTRACT FROM AUTHOR]

The DEP force is usually calculated from the object’s point of view using the interaction of the object’s induced dipole moment with the inducing field. Recently, we described the DEP behavior of high- and low-conductive 200-µm 2D spheres in a square 1 × 1-mm chamber with a plane-versus-pointed electrode configuration from the system’s point of view. Here we extend our previous considerations to the plane-versus-plane and pointed-versus-pointed electrode configurations. The trajectories of the sphere center and the corresponding DEP forces were calculated from the gradient of the system’s overall energy dissipation for given starting points. The dissipation’s dependence on the sphere’s position in the chamber is described by the numerical “conductance field”, which is the DC equivalent of the capacitive charge-work field. While the plane-versus-plane electrode configuration is field-gradient free without an object, the presence of the highly or low-conductive spheres generates structures in the conductance fields, which result in very similar DEP trajectories. For both electrode configurations, the model describes trajectories with multiple endpoints, watersheds, and saddle points, very high attractive and repulsive forces in front of pointed electrodes, and the effect of mirror charges. Because the model accounts for inhomogeneous objectpolarization by inhomogeneous external fields, the approach allows the modeling of the complicated interplay of attractive and repulsive forces near electrode surfaces and chamber edges. Non-reversible DEP forces or asymmetric magnitudes for the highly and low-conductive spheres in large areas of the chamber indicate the presence of higher-order moments, mirror charges, etc.

• Microfluidic assays and advanced imaging technologies provide novel insight toward neutrophil function in individuals with cystic fibrosis (CF). • Neutrophils from individuals with CF display dysfunctional migration, cell-to-cell clustering, and phagocytosis. • Differences were noted between individuals with CF who were well and those experiencing a pulmonary exacerbation. Excessive neutrophil inflammation is the hallmark of cystic fibrosis (CF) airway disease. Novel technologies for characterizing neutrophil dysfunction may provide insight into the nature of these abnormalities, revealing a greater mechanistic understanding and new avenues for CF therapies that target these mechanisms. Blood was collected from individuals with CF in the outpatient clinic, CF individuals hospitalized for a pulmonary exacerbation, and non-CF controls. Using microfluidic assays and advanced imaging technologies, we characterized 1) spontaneous neutrophil migration using microfluidic motility mazes, 2) neutrophil migration to and phagocytosis of Staphylococcal aureus particles in a microfluidic arena, 3) neutrophil swarming on Candida albicans clusters, and 4) Pseudomonas aeruginosa -induced neutrophil transepithelial migration using micro-optical coherence technology (µOCT). Participants included 44 individuals: 16 Outpatient CF, 13 Hospitalized CF, and 15 Non-CF individuals. While no differences were seen with spontaneous migration, CF neutrophils migrated towards S. aureus particles more quickly than non-CF neutrophils (p < 0.05). CF neutrophils, especially Hospitalized CF neutrophils, generated significantly larger aggregates around S. aureus particles over time. Hospitalized CF neutrophils were more likely to have dysfunctional swarming (p < 0.01) and less efficient clearing of C. albicans (p < 0.0001). When comparing trans-epithelial migration towards Pseudomonas aeruginosa epithelial infection, Outpatient CF neutrophils displayed an increase in the magnitude of transmigration and adherence to the epithelium (p < 0.05). Advanced technologies for characterizing CF neutrophil function reveal significantly altered migratory responses, cell-to-cell clustering, and microbe containment. Future investigations will probe mechanistic basis for abnormal responses in CF to identify potential avenues for novel anti-inflammatory therapeutics. [ABSTRACT FROM AUTHOR]

The majority of in vitro studies focusing upon particle–lung cell interactions use static models at an air–liquid interface (ALI). Advancing the physiological characteristics of such systems allows for closer resemblance of the human lung, in turn promoting 3R strategies. PATROLS (EU Horizon 2020 No. 760813) aimed to use a well-characterised in vitro model of the human alveolar epithelial barrier to determine how fluid-flow dynamics would impact the outputs of the model following particle exposure. Using the QuasiVivoTM (Kirkstall Ltd., York, UK) system, fluid-flow conditions were applied to an A549 + dTHP-1 cell co-culture model cultured at the ALI. DQ12 and TiO2 (JRCNM01005a) were used as model particles to assess the in vitro systems’ sensitivity. Using a quasi- and aerosol (VitroCell Cloud12, VitroCell Systems, Waldkirch, Germany) exposure approach, cell cultures were exposed over 24 h at IVIVE concentrations of 1 and 10 (DQ12) and 1.4 and 10.4 (TiO2) µg/cm2, respectively. We compared static and fluid flow conditions after both these exposure methods. The co-culture was subsequently assessed for its viability, membrane integrity and (pro-)inflammatory response (IL-8 and IL-6 production). The results suggested that the addition of fluid flow to this alveolar co-culture model can influence the viability, membrane integrity and inflammatory responses dependent on the particle type and exposure.

Enzymatically induced calcite precipitation (EICP) is an engineering technology that allows for targeted reduction of porosity in a porous medium by precipitation of calcium carbonates. This might be employed for reducing permeability in order to seal flow paths or for soil stabilization. This study investigates the growth of calcium-carbonate crystals in a micro-fluidic EICP setup and relies on experimental results of precipitation observed over time and under flow-through conditions in a setup of four pore bodies connected by pore throats. A phase-field approach to model the growth of crystal aggregates is presented, and the corresponding simulation results are compared to the available experimental observations. We discuss the model's capability to reproduce the direction and volume of crystal growth. The mechanisms that dominate crystal growth are complex depending on the local flow field as well as on concentrations of solutes. We have good agreement between experimental data and model results. In particular, we observe that crystal aggregates prefer to grow in upstream flow direction and toward the center of the flow channels, where the volume growth rate is also higher due to better supply. [ABSTRACT FROM AUTHOR]

This review surveys advances in the fabrication of functional microdevices by multi-photon lithography (MPL) using the SU-8 material system. Microdevices created by MPL in SU-8 have been key to progress in the fields of micro-fluidics, micro-electromechanical systems (MEMS), micro-robotics, and photonics. The review discusses components, properties, and processing of SU-8 within the context of MPL. Emphasis is focused on advances within the last five years, but the discussion also includes relevant developments outside this period in MPL and the processing of SU-8. Novel methods for improving resolution of MPL using SU-8 and discussed, along with methods for functionalizing structures after fabrication.

Highlights • Hydrodynamic cavitation used to remove CRUD from micro-orifices. • CRUD formed under prototypical nuclear reactor operating conditions. • Volume of CRUD reduced by 80–90% in a few minutes of exposure to cavitating flow. • No detectable cavitation-induced damage to the metal surface; • Simplified micro-fluidics configuration relevant for water-cooled nuclear systems. Abstract Chalk river unidentified deposit (CRUD) is an acronym used to describe the corrosion deposits that form in nuclear power plants. Such deposits are often associated to reduction of heat transfer in fuel rods and to blockage of channels in regions of fast hydrodynamic flow. Given the significance of the operational consequences associated to CRUD deposition, the development of methodologies to remove it is of scientific and technical interest. In this study, a microscale flow loop setup, replicating conditions relevant to plant operations, was used to explore the potential of exploiting hydrodynamic cavitation for CRUD removal. Tests were performed on discs with micro-orifices that were previously exposed to high temperature water flow to induce CRUD deposition. CRUD removal from within the micro-orifices was performed by inducing cavitation, and monitored via periodic microstructural examinations. The results indicate that a cavitating regime can reduce the volume of CRUD deposit by 80–90% within minutes, with no detectable damage to the metal surface. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Novel proposed micro-mixers designs are analyzed for mixing index/mixing efficiency. • Effect of Reynolds number on mixing index is investigated. • Effect of pressure drop on mixing index is investigated. • Relationship between Reynolds number and pressure drop is investigated. • Based on this analysis YRCSAR design is concluded having better mixing index. Abstract Three representative types of Y-shaped split and recombination three-dimensional passive micromixers are analyzed for mixing efficiency both experimentally and by numerical simulation. These designs are important because of simple fabrication and better mixing ability. The flow and mixing capability of these mixers are numerically investigated for Reynolds number, in the range of 0.5–100. Mixing index and pressure drop of each micro-mixer design are evaluated in COMSOL 5.2a. All Proposed designs mixing index line graph and images are clearly showing that mixing is much improved as compared to straight mixer YSSAR. It is due to chaotic advection and Dean Flow effect in YCSAR, YRCSAR, and YRSAR that transverse flow mechanism enhance the mixing index. The mixing index of YRCSAR, having both circular and rhombus mixing units is 99% at Reynolds number 100 superior in mixing performance as compared other proposed micro-mixers. Mixers chips are fabricated from borosilicate glass and liquid silicone elastomer material. Red and yellow dye was used for evaluating the mixing performance experimentally. Simulation and experimental images of analyzed micro-mixers as well as the line plots, both shows that with an increase in Reynolds number mixing index increases. As a result of the increase in Reynolds number, there is an increase in the chaotic advection and Dean Flow effect, which creates rotations and vortices and hence improve the mixing index. There is a little difference in experimental and simulation results values but the overall trends are consistent in both cases. [ABSTRACT FROM AUTHOR]

Microfluidics is an active research area in modern fluid mechanics, with several applications in science and engineering. Despite their importance in microfluidic systems, micro-orifices with non-circular cross-sections have not been extensively investigated. In this study, micro-orifice discharge with single-phase liquid flow was experimentally investigated for seven square and rectangular cross-section micro-orifices with a hydraulic diameter in the range of 326–510 µm. The discharge measurements were carried out in pressurized water (12 MPa) at ambient temperature (298 K) and high temperature (503 K). During the tests, the Reynolds number varied between 5883 and 212,030, significantly extending the range in which data are currently available in the literature on non-circular micro-orifices. The results indicate that the cross-sectional shape of the micro-orifice has little, if any, effect on the hydrodynamic behavior. Thus, existing methods for the prediction of turbulent flow behavior in circular micro-orifices can be used to predict the flow behavior in non-circular micro-orifices, provided that the flow geometry of the non-circular micro-orifice is described using a hydraulic diameter.

Micro-orifice discharge with single-phase water flow was experimentally investigated with six multi-micro-orifice test pieces with orifice diameter of 200 µm and thickness to diameter ratio between 4.25 and 27.0. During the experiments the Reynolds number varied between 5 and 4500: a range that corresponds to creeping flow and laminar to turbulent transitional flow. The emergence of turbulence, as indirectly deduced from the change in slope of the pressure drop versus mass flow rate profiles, was found to be gradual and smooth. Using the newly generated data presented here, the validity of an existing micro-orifice discharge prediction method for creeping flow conditions was extended to microfluidics applications with thick micro-orifices. [ABSTRACT FROM AUTHOR]

Micro-orifice discharge with single-phase liquid flow was experimentally investigated with six circular micro-orifices with diameters of 300 μm and 600 μm. The experiments were carried out with water at high pressure (12 MPa) and high temperature (503 K), such that the Reynolds number varied between 28,000 and 220,000, a range significantly wider than inspected during previous researches on turbulent flow conditions in micro-orifices. The dimensionless pressure drop slightly decreased with increasing Reynolds number, with no apparent influence of the micro-orifice diameter ratio or aspect ratio. Using the newly generated data presented here, the validity of an existing micro-orifice discharge prediction method for turbulent flow conditions was extended to microfluidics applications with very high Reynolds numbers. [ABSTRACT FROM AUTHOR]

The capability of isolating and sorting specific types of cells is crucial in life science, particularly for the early diagnosis of lethal diseases and monitoring of medical treatments. Among all the micro-fluidics techniques for cell sorting, inertial focusing combined with the laminar vortex technology is a powerful method to isolate cells from flowing samples in an efficient manner. This label-free method does not require any external force to be applied, and allows high throughput and continuous sample separation, thus offering a high filtration efficiency over a wide range of particle sizes. Although rather recent, this technology and its applications are rapidly growing, thanks to the development of new chip designs, the employment of new materials and microfabrication technologies. In this review, a comprehensive overview is provided on the most relevant works which employ inertial focusing and laminar vortex technology to sort particles. After briefly summarizing the other cells sorting techniques, highlighting their limitations, the physical mechanisms involved in particle trapping and sorting are described. Then, the materials and microfabrication methods used to implement this technology on miniaturized devices are illustrated. The most relevant evolution steps in the chips design are discussed, and their performances critically analyzed to suggest future developments of this technology.

Micro manufacturing is dealing with the fabrication of structures in the order of 0 [...]

Fluid flow in UV nanoimprint lithography with patterned template is simulated to study the effect of pattern directionality on droplet merging, throughput and defectivity. Flow in high density patterns is simulated by using an anisotropic permeability. A method to calculate the permeability for templates with line and space patterns is presented. It is found that the directionality of the pattern results in anisotropic spreading of the droplets. The droplets flow faster in the direction of the pattern resulting in channelized unfilled regions. These regions fill slowly because the permeability in the direction normal to the patterns is low. A modified hexagonal arrangement for droplet dispensing is proposed in which the filling time is lower than square and hexagonal droplet arrangements. Simulations are carried out with different multi-patterned template and droplet dispensing schemes. Dispensing droplets such that their volume is sufficient to fill the features locally is found to be the optimum dispensing scheme to minimize filling time. [ABSTRACT FROM AUTHOR]

Glass micromachining is currently becoming essential for the fabrication of micro-devices, including micro- optical-electro-mechanical-systems (MOEMS), miniaturized total analysis systems (_TAS) and microfluidic devices for biosensing. Moreover, glass is radio frequency (RF) transparent, making it an excellent material for sensor and energy transmission devices. Advancements are constantly being made in this field, yet machining smooth through-glass vias (TGVs) with high aspect ratio remains challenging due to poor glass machinability. As TGVs are required for several micro-devices, intensive research is being carried out on numerous glass micromachining technologies. This paper reviews established and emerging technologies for glass micro-hole drilling, describing their principles of operation and characteristics, and their advantages and disadvantages. These technologies are sorted into four machining categories: mechanical, thermal, chemical, and hybrid machining (which combines several machining methods). Achieved features by these methods are summarized in a table and presented in two graphs. We believe that this paper will be a valuable resource for researchers working in the field of glass micromachining as it provides a comprehensive review of the different glass micromachining technologies. It will be a useful guide for advancing these techniques and establishing new hybrid ones, especially since this is the first broad review in this field. [ABSTRACT FROM AUTHOR]

Highlights from the article: Keywords: micro and nano manufacturing; micro-fluidics; micro-optics; micro and nano additive manufacturing; micro-assembly; surface engineering and interface nanotechnology; micro factories; micro reactors; micro sensors; micro actuators Micro manufacturing is dealing with the fabrication of structures in the order of 0.1 to 1000 µm. The scope of nano manufacturing extends the size range of manufactured features to even smaller length scales: below 100 nm. Last but not the least, this Special Issue reports numerous applications of micro and nano manufacturing technologies with a special focus on micro-optics and micro-fluidics. Micro and nano manufacturing, micro-fluidics, micro-optics, micro and nano additive manufacturing, micro-assembly, surface engineering and interface nanotechnology, micro factories, micro reactors, micro sensors, micro actuators.

Fibers are widely used in different industrial processes, for example in paper manufacturing or lost circulation problems in the oil industry. Recently, interest towards the use of fibers at the microscale has grown, driven by research in bio-medical applications or drug delivery systems. Microfluidic systems are not only directly relevant for lab-on-chip applications, but have also proven to be good model systems to tackle fundamental questions about the flow of fiber suspensions. It has therefore become necessary to provide fiber-like particles with an excellent control of their properties. We present here two complementary in situ methods to fabricate controlled micro-fibers allowing for an embedded fabrication and flow-on-a-chip platform. The first one, based on a photo-lithography principle, can be used to make isolated fibers and dilute fiber suspensions at specific locations of interest inside a microchannel. The self-assembly property of super-paramagnetic colloids is the principle of the second fabrication method, which enables the fabrication of concentrated suspensions of more flexible fibers. We propose a flow gallery with several examples of fiber flow illustrating the two methods' capabilities and a range of recent laminar flow results. [ABSTRACT FROM AUTHOR]

Micro-fluidic systems have been proposed as potential solutions for the cooling of next-generation Integrated Circuits (ICs) and Photonics Integrated Circuits (PICs). For PICs, integration of micro-fluidics may enable greater laser-bar array densities and, consequently, greater transmission bandwidth. To cool the μm scale hot-spots produced by the laser-bars, a passively actuated structure situated in a micro-channel could regulate temperature by disturbing flow in a target location as required. To this end, a proof-of-concept passive structure was developed from a Shape Memory Alloy (SMA), and demonstrated at the millimeter scale in previous work. The objective of this study is to measure the heat transfer augmentation at a target surface downstream of the obstruction. Two experiments were performed to measure the flow field and heat transfer downstream of the test pieces in a square miniature channel for a range of obstruction Reynolds numbers (Re ≈ 50–170) and opening area ratios ( β ≈ 0.2–0.5): using Particle-Image Velocimetry (PIV) and infrared (IR) thermography of a Joule-heated foil respectively. A 50% improvement was observed in the foil area averaged heat transfer coefficient (relative to the unobstructed channel) for Re w = 176 and β = 0.19 . A correlation was developed to interpolate Nusselt number (Nu) from a given Re and β for the studied geometry, and analysis of the correlated exponents showed an improvement in heat transfer relative to a simple pillar obstruction. This was attributed to the wake that formed downstream of the test pieces. The findings of this work are relevant to the modeling and design of practical micro-fluidic systems for targeted hot-spot cooling in future integrated circuit packaging. [ABSTRACT FROM AUTHOR]

Choked cavitation was experimentally investigated with three circular micro-orifices with diameters of 150 μm and 300 μm and thicknesses of 1.04 mm, 1.06 mm and 1.93 mm. Water was used as the test fluid, and experiments were carried out with upstream pressures in the range of 5.1–13.5 MPa. The cavitation number at the inception and cessation of choked cavitation was found to increase with increasing the micro-orifice diameter and thickness. This suggests that micro-orifices could be characterized by very small choked cavitation numbers and therefore might be less susceptible to choking than their macro-scale counterparts. The cavitation number at the inception and cessation of choked cavitation was independent of the upstream pressure, downstream pressure, average flow velocity and orifice Reynolds number. At choking, the ratio of the upstream pressure to the downstream pressure is constant for a given micro-orifice, while during choked flow the mass flow rate through the micro-orifice is proportional to the square root of the upstream pressure. [ABSTRACT FROM AUTHOR]

This paper describes continuous sorting and washing of cancer cells from blood samples by three-dimensional rotating flows and hydrophoretic cell focusing in a microchannel with slant trenches. Sample preparation for analysis of cancer cells such as sorting and washing is an important pre-requisite for their downstream analysis ( i.e. enumeration or molecular characterization of cancer cells). Current cell separators, however, provide the capability of either sorting or washing. Washing process is routinely per- formed off-chip, preventing the automation of cell-based assays and point-of-care diagnostics. We present here a microfluidic method for on-chip cell sorting and washing. Slant trenches on a channel floor generate rotational flow streams and enable manipulation of the streams to passively cross cancer cells which remain focused in their equilibrium position by hydrophoresis. Using this device, we sorted cancer cells from contaminant particles and simultaneously washed them with a clean buffer, achieving high blood cell rejection efficiency of 99.3% and washing efficiency of 99.0%. The device enables simultaneous sorting and washing of cancer cells which can facilitate high-performance, automated cancer cell analysis. [ABSTRACT FROM AUTHOR]

Glass micromachining is currently becoming essential for the fabrication of micro-devices, including micro- optical-electro-mechanical-systems (MOEMS), miniaturized total analysis systems (μTAS) and microfluidic devices for biosensing. Moreover, glass is radio frequency (RF) transparent, making it an excellent material for sensor and energy transmission devices. Advancements are constantly being made in this field, yet machining smooth through-glass vias (TGVs) with high aspect ratio remains challenging due to poor glass machinability. As TGVs are required for several micro-devices, intensive research is being carried out on numerous glass micromachining technologies. This paper reviews established and emerging technologies for glass micro-hole drilling, describing their principles of operation and characteristics, and their advantages and disadvantages. These technologies are sorted into four machining categories: mechanical, thermal, chemical, and hybrid machining (which combines several machining methods). Achieved features by these methods are summarized in a table and presented in two graphs. We believe that this paper will be a valuable resource for researchers working in the field of glass micromachining as it provides a comprehensive review of the different glass micromachining technologies. It will be a useful guide for advancing these techniques and establishing new hybrid ones, especially since this is the first broad review in this field.

• Tapered rectanglar micro-chips are designed to produce mono-dispersed fluid cells. • Self-scaling processes are revealed to build up a self-similarity scaling frame. • The Pan-dripping and the Pan-jetting regime are clearly distinguished by machine learning. • The universal self-scalings are valid for all drop-detaching flow patterns. Experiments are carried out to explored the co-flows in a type of novel tapered rectanglar PMMA micro-channels. Variations of geometric parameter combinations bring great complexity to systematic descriptions of the co-flow behaviors. We find that the tapered co-flows are self-scaling processes. Based on theory of similitude, a self-similarity frame is buildup to reduce the complexity and dimension of the problem. Under such frame, universal scaling laws covering all the drop-detaching regimes (i.e., slug, dripping, thin jet) are derived, concisely and persuasively. The droplet length depends on the flow-rate-ratio and gives an exponential of nearly 1 / 2 , which is featured as a typical ′ Flow-Rate-Controlled-Flow ′. The drop-detaching frequency depends on the two-phase capillary number and gives an exponential of nearly 3. Note that, these two formulas are valid in all the drop-detaching regimes over differed physical mechanisms. Moreover, the most astonishing thing is that, the former formula reproduce the scaling law of thin jet regime in straight circular co-flows, while the later one reproduce the scaling law of dripping regime in straight circular co-flows at the same time. Such highly consistency of scalings were rarely reported before. Furthermore, the clusters of the flow maps can be degenerated into one single flow diagram under our self-similarity frame. Such diagram can be divided naturally by machining learning into two parts, the Pan-dripping regime and the Pan-jetting regime, which are clear bordered at We d ≈ 1 and Ca c ≈ 0.28. These critical values are also consistent with the results in straight circular co-flows. This work can greatly facilitate the design and analysis method of devices for flow manipulation via simple formulas that catch the parameter range of liquid cells. [ABSTRACT FROM AUTHOR]

We present a method to supply oxygen to on-chip stored aqueous droplets surrounded by oxygen-permeable fluorinated oil in micro-channels. By generating air-droplets (air-bubbles) in between the aqueous droplets, oxygen diffuses to those aqueous droplets. This is confirmed by experiments comparing the effect of nitrogen bubbles and air-bubbles. The proposed method and device are a step towards long-term on-chip cultivation of mammalian cells and aerobic bacteria growth in droplets. [ABSTRACT FROM AUTHOR]

We present a novel approach to measure optical absorption spectra with spatial resolution at the micron scale. The setup combines a continuous white light excitation beam in transmission geometry with a confocal microscope. The spatial resolution is found to be better than 1.4 μm in the lateral and 3.6 μm in the axial direction. Employing multichannel detection the absorption spectrum of hemoglobin in a single red blood cell is measured on the timescale of seconds. Through measurements of the transmitted intensity in solutions in nanoliter quantities we establish that the absorbance varies linearly with concentration. Our setup enables the investigation of spatial variations in the optical density of small samples on the micron scale and can be applied to the study of biological assemblies at the single cell level, in optical diagnostics, and in micro-fluidics. [ABSTRACT FROM AUTHOR]

We present new hybrid molecular-continuum simulations of water flow through filtration membranes. The membranes consist of aligned carbon nanotubes (CNTs) of high aspect ratio, where the tube diameters are ~1-2 nm and the tube lengths (i.e. the membrane thicknesses) are 2-6 orders of magnitude larger than this. The flow in the CNTs is subcontinuum, meaning standard continuum fluid equations cannot adequately model the flow; also, full molecular dynamics (MD) simulations are too computationally expensive for modelling these membrane thicknesses. However, various degrees of scale separation in both time and space in this problem can be exploited by a multiscale method: we use the serial-network internal-flow multiscale method (SeN-IMM). Our results from this hybrid method compare very well with full MD simulations of flow cases up to a membrane thickness of 150 nm, beyond which any full MD simulation is computationally intractable. We proceed to use the SeN-IMM to predict the flow in membranes of thicknesses 150 nm-2 μm, and compare these results with both a modified Hagen-Poiseuille flow equation and experimental results for the same membrane configuration. We also find good agreement between experimental and our numerical results for a 1-mm-thick membrane made of CNTs with diameters around 1.1 nm. In this case, the hybrid simulation is orders of magnitude quicker than a full MD simulation would be. [ABSTRACT FROM AUTHOR]

Some physical experiments exhibit size-dependency for fluid flows at small scales. This in turn necessitates the introduction of couple-stresses in the corresponding continuum theory. The resulting size-dependent couple stress fluid mechanics can be used to explore a range of such non-Newtonian flow behavior at micro- and nano-scales, and also to bridge between atomistic and classical continuum theories. Here we concentrate on two-dimensional flow and examine the effects of couple-stresses by developing and then applying a stream function-vorticity computational fluid dynamics formulation. Details are provided both on the governing equations for size-dependent flow and on the corresponding numerical implementation. Afterwards, the formulation is applied to the lid-driven cavity problem to examine the behavior of the flow as a function of the length scale parameter l . The investigation covers a range of Reynolds numbers, and includes an evaluation of the critical value beyond which a stationary response is no longer possible. The additional boundary conditions associated with consistent couple stress theory are found to play an important role in determining the flow pattern and critical Reynolds number. [ABSTRACT FROM AUTHOR]

Silicon micro-channel cooling is being studied for efficient thermal management in application fields such as high power computing and 3D electronic integration. This concept has been introduced in 2010 for the thermal management of silicon pixel detectors in high energy physics experiments. Combining the versatility of standard micro-fabrication processes with the high thermal efficiency typical of micro-fluidics, it is possible to produce effective thermal management devices that are well adapted to different detector configurations. The production of very thin cooling devices in silicon enables a minimization of material of the tracking sensors and eliminates mechanical stresses due to the mismatch of the coefficient of thermal expansion between detectors and cooling systems. The NA62 experiment at CERN will be the first high particle physics experiment that will install a micro-cooling system to perform the thermal management of the three detection planes of its Gigatracker pixel detector. [ABSTRACT FROM AUTHOR]

The dimensionless pressure drop was measured for six micro-orifices with diameters of 150 μm, 300 μm and 600 μm, and thickness ratios between 1.87 and 6.93. The experiments were carried out with water for orifice Reynolds number between 6000 and 25,000, thus extending the range covered in previous researches in turbulent flow conditions. The dimensionless pressure drop was found to be a weak decreasing function of the Reynolds number, and was found to be unaffected by the micro-orifice diameter ratio or thickness ratio. The static pressure profiles measured immediately downstream of the micro-orifices were flat, indicating that the vena contracta is located within the micro-orifice. A new prediction method for the dimensionless pressure drop in micro-orifices at high Reynolds number was developed using available data. [ABSTRACT FROM AUTHOR]

Fibers are widely used in different industrial processes, for example in paper manufacturing or lost circulation problems in the oil industry. Recently, interest towards the use of fibers at the microscale has grown, driven by research in bio-medical applications or drug delivery systems. Microfluidic systems are not only directly relevant for lab-on-chip applications, but have also proven to be good model systems to tackle fundamental questions about the flow of fiber suspensions. It has therefore become necessary to provide fiber-like particles with an excellent control of their properties. We present here two complementary in situ methods to fabricate controlled micro-fibers allowing for an embedded fabrication and flow-on-a-chip platform. The first one, based on a photo-lithography principle, can be used to make isolated fibers and dilute fiber suspensions at specific locations of interest inside a microchannel. The self-assembly property of super-paramagnetic colloids is the principle of the second fabrication method, which enables the fabrication of concentrated suspensions of more flexible fibers. We propose a flow gallery with several examples of fiber flow illustrating the two methods’ capabilities and a range of recent laminar flow results.

The hydrodynamic behavior of time-periodic electro-kinetic-driven flow in a microannular channel is examined based on the linearized Poisson-Boltzmann equation and the Navier-Stokes equation under various periodic functions. The response of the flow field to excitation by more complex waveforms (than the sine wave) is investigated using Green's function approach. It is shown that the velocity profiles are characterized by the geometric radius ratio, the wall zeta potential ratio, the electro-kinetic radius, and the dimensionless frequency. The influence of the particular excitation waveform is demonstrated to be more significant at lower frequencies, since the bulk fluid has more time to respond to instantaneous changes in the applied unsteady field. The square waveform yields higher local velocities (compared with the others), since the full strength of the electric field is applied for a longer time. In cases of high excitation frequency, large annulus size or small kinematic viscosity, the flow is demonstrated to be confined to a region near the annulus walls while the bulk fluid remains essentially stationary. As the dimensionless frequency becomes less than one, momentum diffusion is faster than the period of oscillation, and the plug-like velocity profiles (similar to steady-state electroosmotic flow) are observed at nearly all times. Impulsively started flows (from rest) exhibit transient behavior resulting in a net positive flow during the initial cycles for cases of high non-dimensional frequency. [ABSTRACT FROM AUTHOR]

Ultrasonic standing waves (USW) separation is an established technology for micro scale applications due to the excellent control to manipulate particles acoustically achieved when combining high frequency ultrasound with laminar flow in microchannels, allowing the development of numerous applications. Larger scale systems (pilot to industrial) are emerging; however, scaling up such processes are technologically very challenging. This paper reviews the physical principles that govern acoustic particle/droplet separation and the mathematical modeling techniques developed to understand, predict, and design acoustic separation processes. A further focus in this review is on acoustic streaming, which represents one of the major challenges in scaling up USW separation processes. The manuscript concludes by providing a brief overview of the state of the art of the technology applied in large scale systems with potential applications in the dairy and oil industries. [ABSTRACT FROM AUTHOR]

Rapid Reconstitution Packages (RRPs) are portable platforms that integrate microfluidics for rapid reconstitution of lyophilized drugs. Rapid reconstitution of lyophilized drugs using standard vials and syringes is an error-prone process. RRPs were designed using computational fluid dynamics (CFD) techniques to optimize fluidic structures for rapid mixing and integrating physical properties of targeted drugs and diluents. Devices were manufactured using stereo lithography 3D printing for micrometer structural precision and rapid prototyping. Tissue plasminogen activator (tPA) was selected as the initial model drug to test the RRPs as it is unstable in solution. tPA is a thrombolytic drug, stored in lyophilized form, required in emergency settings for which rapid reconstitution is of critical importance. RRP performance and drug stability were evaluated by high-performance liquid chromatography (HPLC) to characterize release kinetics. In addition, enzyme-linked immunosorbent assays (ELISAs) were performed to test for drug activity after the RRPs were exposed to various controlled temperature conditions. Experimental results showed that RRPs provided effective reconstitution of tPA that strongly correlated with CFD results. Simulation and experimental results show that release kinetics can be adjusted by tuning the device structural dimensions and diluent drug physical parameters. The design of RRPs can be tailored for a number of applications by taking into account physical parameters of the active pharmaceutical ingredients (APIs), excipients, and diluents. RRPs are portable platforms that can be utilized for reconstitution of emergency drugs in time-critical therapies. [ABSTRACT FROM AUTHOR]

Abstract: Ripples are formed on the surface of solid materials after interaction with laser pulses of high intensity/irradiance. When ultra-short sub-1ps laser pulses are used, the observed morphology of ripples on surfaces becomes much more complex as compared with ripples formed by long laser pulses. Uniquely for the short laser pulses, ripples can be formed in the bulk. A better understanding of the fundamentals of light-matter interaction in ripples formation is strongly required. Experimentally observed ripples and dependence of their parameters on laser fabrication conditions and material properties are summarized first. Then, a critical review of relevant ripple formation mechanisms is presented, discussed, and formation conjectures are presented. It is shown that formation of plasma at sub-critical or critical densities (i.e., solid state or breakdown plasmas) on the surface and in the bulk specific to the high-intensity ultra-short laser pulses has to be considered to account for the experimental observations. Surface and bulk ripples formed on/in dielectrics can be explained by the same model where electron–hole (solid state) plasma is formed at the very threshold of ripples formation. Ripple patterns have a strong application potential from sensing to light harvesting and (photo)catalysis mainly due to nanoscale features and self-replication of pattern over large macroscopic areas. Several emerging applications are shown. [Copyright &y& Elsevier]