Fluidic System Research Articles

Accelerating multiscale modelling of fluids with on-the-fly Gaussian process regression

We present a scheme for accelerating hybrid continuum-atomistic models in multiscale fluidic systems by using Gaussian process regression as a surrogate model for computationally expensive molecular dynamics simulations. Using Gaussian process regression, we are able to accurately predict atomic-scale information purely by consideration of the macroscopic continuum-model inputs and outputs and judge on the fly whether the uncertainty of our prediction is at an acceptable level, else a new molecular simulation is performed to continually augment the database, which is never required to be complete. This provides a substantial improvement over the current generation of hybrid methods, which often require many similar atomistic simulations to be performed, discarding information after it is used once. We apply our hybrid scheme to nano-confined unsteady flow through a high-aspect-ratio converging–diverging channel, and make comparisons between the new scheme and full molecular dynamics simulations for a range of uncertainty thresholds and initial databases. For low thresholds, our hybrid solution is highly accurate—around that of thermal noise. As the uncertainty threshold is raised, the accuracy of our scheme decreases and the computational speed-up increases (relative to a full molecular simulation), enabling the compromise between accuracy and efficiency to be tuned. The speed-up of our hybrid solution ranges from an order of magnitude, with no initial database, to cases where an extensive initial database ensures no new MD simulations are required.

Microfluidic active loading of single cells enables analysis of complex clinical specimens

A fundamental trade-off between flow rate and measurement precision limits performance of many single-cell detection strategies, especially for applications that require biophysical measurements from living cells within complex and low-input samples. To address this, we introduce ‘active loading’, an automated, optically-triggered fluidic system that improves measurement throughput and robustness by controlling entry of individual cells into a measurement channel. We apply active loading to samples over a range of concentrations (1–1000 particles μL−1), demonstrate that measurement time can be decreased by up to 20-fold, and show theoretically that performance of some types of existing single-cell microfluidic devices can be improved by implementing active loading. Finally, we demonstrate how active loading improves clinical feasibility for acute, single-cell drug sensitivity measurements by deploying it to a preclinical setting where we assess patient samples from normal brain, primary and metastatic brain cancers containing a complex, difficult-to-measure mixture of confounding biological debris.

Automated high-throughput light-sheet fluorescence microscopy of larval zebrafish.

Light sheet fluorescence microscopy enables fast, minimally phototoxic, three-dimensional imaging of live specimens, but is currently limited by low throughput and tedious sample preparation. Here, we describe an automated high-throughput light sheet fluorescence microscope in which specimens are positioned by and imaged within a fluidic system integrated with the sheet excitation and detection optics. We demonstrate the ability of the instrument to rapidly examine live specimens with minimal manual intervention by imaging fluorescent neutrophils over a nearly 0.3 mm3 volume in dozens of larval zebrafish. In addition to revealing considerable inter-individual variability in neutrophil number, known previously from labor-intensive methods, three-dimensional imaging allows assessment of the correlation between the bulk measure of total cellular fluorescence and the spatially resolved measure of actual neutrophil number per animal. We suggest that our simple experimental design should considerably expand the scope and impact of light sheet imaging in the life sciences.

Temperature-Corrected Fluidic Glucose Sensor Based on Microwave Resonator.

In this paper, a fluidic glucose sensor that is based on a complementary split-ring resonator (CSRR) is proposed for the microwave frequency region. The detection of glucose with different concentrations from 0 mg/dL to 400 mg/dL in a non-invasive manner is possible by introducing a fluidic system. The glucose concentration can be continuously monitored by tracking the transmission coefficient as a sensing parameter. The variation tendency in by the glucose concentration is analyzed with equivalent circuit model. In addition, to eradicate the systematic error due to temperature variation, the sensor is tested in two temperature conditions: the constant temperature condition and the time-dependent varying temperature condition. For the varying temperature condition, the temperature correction function was derived between the temperature and the variation in for DI water. By applying the fitting function to glucose solution, the subsidiary results due to temperature can be completely eliminated. As a result, the varies by 0.03 dB as the glucose concentration increases from 0 mg/dL to 400 mg/dL.

Optofluidic Modular Blocks for On-Demand and Open-Source Prototyping of Microfluidic Systems.

Rapid prototyping of microfluidic devices has advanced greatly, along with the development of 3D printing and micromachining technologies. However, peripheral systems for microfluidics still rely on conventional equipment, such as bench-top microscopy and syringe pumps, which limit system modification and further improvements. Herein, optofluidic modular blocks are presented as discrete elements to modularize peripheral optical and fluidic systems and are used for on-demand and open-source prototyping of whole microfluidic systems. Each modular block is fabricated by embedding optical or fluidic devices into the corresponding 3D-printed housing. The self-interlocking structure of the modular blocks enables easy assembly and reconfiguration of the blocks in an intuitive manner, while also providing precise optical and fluidic alignment between the blocks. With the library of standardized modular blocks developed here, how the blocks can be easily assembled to build whole microfluidic systems for blood compatibility testing, droplet microfluidics, and cell migration assays is demonstrated. Based on the simplicity of assembling the optofluidic blocks, the prototyping platform can be easily used for open-source sharing of digital design files, assembly and operation instructions, and block specifications, thereby making it easy for nonexperts to implement microfluidic ideas as physical systems.

Scaffolds in a shell-a new approach combining one-photon and two-photon polymerization.

We report on a laser system combining one-photon and two-photon polymerization for precise and fast fabrication of macroscopic three-dimensional structures featuring microscale and nanoscale characteristics. This single-stage process significantly reduces the production time as demonstrated by scaffolds in a shell application. Porous scaffolds with different pore sizes are surrounded by a ring so that cells can be seeded directly to the scaffolds kept in a shell and do not spread over the whole substrate expecting a saving of cell suspension, faster growth on the scaffolds, and a more controllable environment. Compared to a two-photon polymerization process, the ring is fabricated about 500 times faster using one-photon polymerization. The presented hybrid process qualifies for further applications illustrated by a fluidic system.

Air-water interfacial fluidic sonolysis in superhydrophobic silicon-nanowire-embedded system for fast water treatment

The widespread presence of organic pollutants in water resources poses potentially grave health and environment problems. Oxidation processes, which involve in situ generation of reactive oxidant species, are widely employed to treat and remove the pollutants. The conventional advanced oxidation processes (AOPs) typically utilize energy sources and/or additives including catalysts, but the treatment time is still too long. Here, we devise a novel fluidic sonolysis system with a superhydrophobic Si nanowire structured channel, providing an air-water interfacial cavitation for efficient generation of OH· that is promoted by the structure itself without any additional energy inputs or additives. The system removes various organic pollutants including 4-chlorophenol, bisphenol A, carbamazepine and propranolol completely within 12 min, as opposed to hours needed by other AOPs. These results substantiate the promise of the air-water interfacial fluidic sonolysis system for fast and continuous-flow water treatment.

Realization and AC modeling of electronic circuits with water-gated field effect transistors (WG-FETs) based on gate probe distance

We present AC modeling of WG-FET devices based on gate probe distance. Small- and large-signal models are proposed. It is shown that unity gain frequency is inversely proportional to gate distance. Also, common source amplifier, inverter, and ring oscillator circuits are fabricated with WG-FET devices, which use 16 nm-thick mono-Si film as channel layer, for the first time. Circuit simulations are performed based on AC models. Results are verified with experimental measurements using de-ionized (DI) water. For common source amplifier, fUG is measured as 21 Hz for 2 mm gate distance, and it is increased to 1.2 kHz when gate distance is decreased to 200 μm. For inverter, rail-to-rail operation is observed with tPLH of 24 ms and tPHL of 58 ms for 1 square-wave input signal at 1 Hz. Gain is measured as −11 V/V at switching threshold. Ring oscillator is realized with five inverters. A square-wave output signal with amplitude of 840 and frequency of 2.6 Hz is obtained. AC modeling of WG-FET enables realization of advanced circuits which are inherently compatible with fluidic systems. Therefore, they can be valuable assets especially in microfluidic applications.

Electroconvective Cavity Flow Patterns Created by Asymmetric Electrode Configuration

This paper is an experimental study on electroconvective flows produced by an asymmetric electric field in a cavity. It is part of a scientific project aiming to develop electrohydrodynamic (EHD) flow actuator in order to enhance heat transfer and mixing efficiency in fluidic and microfluidic systems. In this study, the EHD flow is obtained by applying a dc voltage between two electrodes (cylinder/plane) immersed in a working liquid. The produced velocity fields strongly depend on the applied voltage. Whatever may be the applied voltage, the fluid goes from the cylinder toward the plate or the other way round. The velocity fields obtained by particle image velocimetry for different potentials are analyzed in both cases with the usual mechanisms (injection and conduction) at the origin of the motion of the liquid. A discussion on the transition between injection and conduction phenomena is finally presented.

Monitoring Aquaculture Water Quality: Design of an Early Warning Sensor with Aliivibrio fischeri and Predictive Models.

A novel toxicity-warning sensor for water quality monitoring in recirculating aquaculture systems (RAS) is presented. The design of the sensor system mainly comprises a whole-cell biosensor. Aliivibrio fischeri, a luminescent bacterium widely used in toxicity analysis, was tested for a mixture of known fish-health stressors, namely nitrite, un-ionized ammonia, copper, aluminum and zinc. Two toxicity predictive models were constructed. Correlation, root mean squared error, relative error and toxic behavior were analyzed. The linear concentration addition (LCA) model was found suitable to ally with a machine learning algorithm for prediction of toxic events, thanks to additive behavior near the limit concentrations for these stressors, with a root-mean-squared error (RMSE) of 0.0623, and a mean absolute error of 4%. The model was proved to have a smaller relative deviation than other methods described in the literature. Moreover, the design of a novel microfluidic chip for toxicity testing is also proposed, which is to be integrated in a fluidic system that functions as a bypass of the RAS tank to enable near-real time monitoring. This chip was tested with simulated samples of RAS water spiked with zinc, with an EC50 of 6,46E-7 M. Future work will be extended to the analysis of other stressors with the novel chip.

An IoT Solution for Online Monitoring of Anesthetics in Human Serum Based on an Integrated Fluidic Bioelectronic System.

In this paper, we present the design, the implementation and the validation of a novel Internet of Things (IoT) drug monitoring system for the online continuous and simultaneous detection of two main anesthetics, e.g., propofol and paracetamol, in undiluted human serum. The described full system consists of a custom-built electronic Raspberry Pi (RPi) based Printed Circuit Board (PCB) that drives and reads out the signal from an electrochemical sensing platform integrated into a fluidic system. Thanks to the Polydimethylsiloxane (PDMS) fluidic device, the analyzed sample is automatically fluxed on the sensing site. The IoT network is supported by a Cloud system, which allows the doctor to control and share all the patient's data through a dedicated Android application and a smart watch. The validation closes with the first ever demonstration that our system successfully works for the simultaneous monitoring of propofol and paracetamol in undiluted human serum by measuring the concentration trends of these two drugs in fluxing conditions over time.

Tandem column isolation of zirconium-89 from cyclotron bombarded yttrium targets using an automated fluidic platform: Anion exchange to hydroxamate resin columns

The development of a tandem column purification method for the preparation of high-purity 89Zr(IV) oxalate is presented. The primary column was a macroporous strongly basic anion exchange resin on styrene divinylbenzene co-polymer. The secondary column, with an internal volume of 33 μL, was packed with hydroxamate resin. A condition of inverted selectivity was developed, whereby the 89Zr eluent solution for the primary column is equivalent to the 89Zr load solution for the secondary column. The ability to transfer 89Zr from one column to the next allows two sequential column clean-up methods to be performed prior to the final elution of the 89Zr(IV) oxalate. This approach assures delivery of high purity 89Zr product and assures a 89Zr product that is eluted in a substantially smaller volume than is possible when using the traditionally-employed single hydroxamate resin column method. The tandem column purification process has been implemented into a prototype automated fluidic system. The system is configured with on-line gamma detection so column effluents can be monitored in near-real time. The automated method was tested using seven cyclotron bombarded Y foil targets. It was found that 95.1 ± 1.3% of the 89Zr present in the foils was recovered in the secondary column elution fraction. Furthermore, elution peak analysis of several 89Zr elution profile radiochromatograms made possible the determination of 89Zr recovery as a function of volume; a 89Zr product volume that contains 90% of the mean secondary column elution peak can be obtained in 0.29 ± 0.06 mL (representing 86 ± 5% of the 89Zr activity in the target). This product volume represents a significant improvement in radionuclide product concentration over the predominant method used in the field. In addition to the reduced 89Zr product elution volume, titrations of the 89Zr product with deferoxamine mesylate salt across two preparatory methods resulted in mean effective specific activity (ESA) values of 279 and 340 T Bq·mmole−1 and mean bindable metals concentrations ([MB]) of 13.5 and 16.7 nmole·g−1. These ESA and [MB] values infer that the 89Zr(IV) oxalate product resulting from this tandem column isolation method has the highest purity reported to date.

Photosensitive Electrified Water/Oil Interfaces Studied By Scanning Electrochemical Microscopy

The interface formed between two immiscible electrolytes solutions (ITIES) is a defect-free (down to the molecular level), self-healing, renewable and conductive substrate for the preferential and controlled formation of molecular assemblies and nano-objects.1 Similar to solid electrodes, modifier layer(s) can be formed and characterized by charge transfer processes across the interfaces. The potential drop across the interface can be controlled externally by using a potentiostat or chemically by dissolving a common salt in both phases. The polarization can be used to drive charged semiconductor nanoparticles to the interface. Polarization could also effectively drive the photo-induced charge transfer reaction by e- or h+ to control evolution of H2 with molecular photosensitizer2 and O2 semiconductor nanomaterials assembled at the ITIES.3 The jump in hydrophobicity at the soft interface supports the spatial separation of charge carriers on either side which partially restricts the recombination processes. Mechanistic studies of charge transfer in photoactivity of semiconductors at polarized ITIES are crucial for evaluation of such interfaces for fluidic systems with the ultimate goal of linking such interfaces to a z-scheme for water splitting. We probe the photo-induced electron transfer reaction at polarized soft interface by integrating it into scanning electrochemical microscope (SECM) as a tool to analyse the kinetics of the interfacial reaction at the nanostructured BiVO4|butyronitrile interphase under chemically controllable Galvani potential difference tuned by variation of ClO4 - concentration ration between the two liquid phases.4 This reaction occurs between electron in conduction band of BiVO4 and [Co(bpy)3]3+ in the organic electrolyte. SECM feedback approach curves are recorded based on the regeneration of the oxidized form of initial [Co(bpy)3]2+ by using the microelectrode (ME) in organic phase as probe. The current is enhanced under illumination with visible light (Scheme A). Furthermore, using substrate generation-tip/collection mode of SECM, O2 is probed as a main product of the photogenerated hole transfer in the aqueous phase under variable interfacial polarization (Scheme B). We also present a novel application of surface interrogation (SI) mode of SECM for in situ evaluate the surface of BiVO4 in photo-assisted water oxidation reaction (WOR). A micropipette (MP) filled with aqueous solution of dispersed nanostructured BiVO4, as a well-defined photosensitized substrate, is immersed into an immiscible organic solution containing perchlorate as common anion to generate the hydroxyl radicals (OH•) as intermediates of WOR under chemically controlled polarization. By the help of a ME as probe, surface concentrations of intermediates (Γ) and kinetics of their decay by bimolecular reactions (k) are analysed by recording the ME chronoamperograms transients enhanced by intermittent illumination of the substrate. Figure 1: Schematic of the SECM invetigation of photocatalysts asembled at liquid-liquid interfaces. A) Extraction of electons by SECM mediator, B) Detection of oxygen evolution, c) Surface interrogation of adobred intermediates. References L. Poltorak, A. Gamero-Quijano, G. Herzog, A. Walcarius, Appl Mater Today 2017, 9, 533-550. L. Rivier, P. Peljo, L.A.C. Vannay, H.H. Girault, Angew. Chem., Int. Ed. 2017, 56, 2324-2327.3. S. Rastgar, M. Pilarski, G. Wittstock, Commun. 2016, 52, 11382-11385.S. Rastgar, G. Wittstock, J. Phys. Chem. C 2017, 121, 25941-25948. Figure 1

High-resolution Patterning Using Two Modes of Electrohydrodynamic Jet: Drop on Demand and Near-field Electrospinning.

Electrohydrodynamic (EHD) jet printing has drawn attention in various fields because it can be used as a high-resolution and low-cost direct patterning tool. EHD printing uses a fluidic supplier to maintain the extruded meniscus by pushing the ink out of the nozzle tip. The electric field is then used to pull the meniscus down to the substrate to produce high-resolution patterns. Two modes of EHD printing have been used for fine patterning: continuous near-field electrospinning (NFES) and dot-based drop-on-demand (DOD) EHD printing. According to the printing modes, the requirements for the printing equipment and ink viscosity will differ. Even though two different modes can be implemented with a single EHD printer, the realization methods significantly differ in terms of ink, fluidic system, and driving voltage. Consequently, without a proper understanding of the jetting requirements and limitations, it is difficult to obtain the desired results. The purpose of this paper is to present a guideline so that inexperienced researchers can reduce the trial and error efforts to use the EHD jet for their specific research and development purposes. To demonstrate the fine-patterning implementation, we use Ag nanoparticle ink for the conductive patterning in the protocol. In addition, we also present the generalized printing guidelines that can be used for other types of ink for various fine-patterning applications.

PO-179 Identification of C-Met and insulin receptor heterodimer as a mediator for hepatocellular carcinoma

IntroductionHepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths and obesity is predicted to be the leading cause for HCC in the following decades. Hyperglycemia and hyperinsulinemia are the two obesity-related factors associated with poor prognosis and survival. Hepatocyte growth factor (HGF) receptor, c-Met overactivation is common and results in higher proliferation and metastasis of HCC cells and drug resistance. In HCC patients, c-Met activation is often observed in the absence of HGF.Material and methodsCells were starved for 24 hours before hyperglycemic (HG, 25 mM) and/or hyperinsulinemic (HI, 100 nM) induction. Lysates were analysed by western blotting using the antibodies detecting activatory phosphorylations of c-Met, IR, Erk 1/2 and Akt. Receptor dimerization was studied by coimmunoprecipitation and colocalization using live-cell imaging. c-Met(SU11274) and IR(HMPA-(AM)3) inhibitors were used to reverse the effects of activations. Tumour cell metabolism was analysed using Seahorse Analyzer with cells expressing predominantly either IR isoform A or B. Proliferation and adhesion capacities were investigated using real time cell analysis system xCELLigence for 96 hours. Tumour cell survival in HG/HI blood circulation was simulated by circulation under shear stress for 4 hours in a fluidic system. Migration and invasion are studied using Boyden chamber.Results and discussions c-Met expression and activation was elevated when induced by high glucose/insulin. Also c-Met and IR were found to form a heterodimer upon HG/HI induction which explains a mechanism of c-Met activation even when HGF is absent in the tumour microenvironment. Both IR isoforms A/B were found to colocalize with c-Met and mediate the effect. In the presence of inhibitors, receptor activations and colocalizations were disrupted. c-Met inhibition resulted in a shift in tumour cell metabolism; diminished glycolysis and oxidative phosphorylation, which offers a role for rendering the cells more aggressive. Elevated adhesion, proliferation, migration, invasion and survival were observed upon induction which are controlled by Erk 1/2 and Akt activations, reversed by c-Met inhibition.ConclusionHere we identified that obesity-related prognostic factors, hyperglycemia and hyperinsulinemia, increase invasive and metastatic capacity of HCC cells through transactivation of c-Met by IR, which might also be a mechanism for drug resistance and offer an approach for targeted therapy.

Abstract 5645: Critical variables to reduce Western blot variability

Abstract Reliable immunodetection of proteins is a critical step in the discovery of new biomarkers and diagnostic. The immunodetection protocol consists of multiple steps including blocking of nonspecific binding sites, incubation using primary and secondary antibodies and extensive washing between steps that easily introduce bias and errors. The quality and reproducibility of results depends on multiple subjective and objective factors such as the qualification and technical skills of the personnel performing the assay and the accuracy of temporal and temperature control, especially during the immunodetection step. BlotCycler™, automated western blot processor, use fluidic control system that allows to eliminate the variability associated with immunodetection and to achieve higher sensitivity by optimized washing procedure. We used BlotCycler to analyze critical source of errors during immunodetection. Relatively small changes in duration and temperature of incubation significantly affect not only the intensity of signal but also the specificity of antibody interaction with antigen. Automated immunodetection at 4ºC significantly improve the specificity of detection and sensitivity that allows reproducible detection of low expressing proteins. Automated processing using BlotCycler allows optimization and control of critical variables leading to improved reproducibility and specificity of immunodetection and should be routinely used for new biomarker discovery and diagnostics, reliable protein quantification, primary antibody specificity testing, and optimization of primary and secondary antibodies concentrations. Citation Format: Russ Yukhananov, Alex Margulis. Critical variables to reduce Western blot variability [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5645.

Abstract 5779: CDK4/6 inhibitors and anaplastic thyroid cancer: An investigation into the retinoblastoma cancer pathway and potential therapeutic targets

Abstract Introduction/Background: Recently, Cyclin-dependent kinase (CDK) 4/6 inhibitors have been shown to increase progression-free survival in estrogen receptor-positive, stage IV breast cancer patients. We aim to assess whether Palbociclib, a selective CDK4/6 inhibitor, prevents tumor cell growth in vitro and in vivo in anaplastic thyroid cancer (ATC). ATC carries an automatic stage IV classification and a 6-month survival prognosis; there has been very little advancement in chemotherapeutic options, making it a good disease target for this new class of drug. Retinoblastoma (Rb) is a tumor suppressor protein that is rarely mutated in ATC (<3%). It blocks cell entry into S phase, preventing DNA synthesis and cell proliferation. Hyper-phosphorylation of Rb by CDK4/6 causes the release of transcription factors and induces cell division. By blocking CDK4/6 with the inhibitor, the tumor suppressor function of Rb stays activated. Methods: We characterized our large library of thyroid cancer cell lines by mRNA and proteins involved in the Rb pathway using qPCR and western blot. We then performed 72-hour dose-dependent cell growth assays using viable cell counts with differing concentrations of Palbociclib to determine EC50 values. The same cell counting technique was used to test Palbociclib in combination with other targeted chemotherapy agents and again in resistance/adaptation experiments with long term exposure. Cell cycle analysis was performed using BD FACSCanto II fluidics system. Results: Our human lines show more susceptibility compared to murine lines. Interestingly, the PI3K and RAS pathway-activating mutated lines required the highest relative doses of Palbociclib followed by p53 and BRAF mutated cells. The Rb negative cells showed no growth inhibition when treated. Using flow cytometry, it was confirmed that Palbociclib's cystostatic effect is due to a G1 arrest. The presence of synergistic effects between Palbociclib and Omipalisib, a PI3K inhibitor, occurs in the majority of the cell lines and preliminary experiments show this combination treatment slows the development of resistance to Palbociclib. Conclusions: In vitro testing has shown that Palbociclib causes dose-dependent growth inhibition on Rb positive ATC cells, and genetic mutations may predict response to the drug. Rb protein is necessary for the drug to have effect. Current work is focused on designing a novel mouse model for in vivo study and to further investigate the related parallel pathways for combined targeted therapies, namely those whose over-activation is associated with the least sensitivity to Palbociclib - PI3K/AKT and RAS pathways. Citation Format: Kristen A. Wong, Antonio Di Cristofano. CDK4/6 inhibitors and anaplastic thyroid cancer: An investigation into the retinoblastoma cancer pathway and potential therapeutic targets [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5779.

Measurement of pressure around porous membranes using a cell pressure probe

Estimating pressure variation is essential in membrane systems because it is the primary factor that affects the energy for system operation. Although numerous researches were conducted studies, most previous studies focused on the hydraulic roles of single membrane. In this study, we examined the pressure variations caused by membranes considering the effects of flow rate, number of membranes, and distance between the membranes. Membranes were integrated into a tygon tube and pressure was measured by using a cell pressure probe with the lapse of time. We evaluated theoretical pressure values by using Poiseuille’s law and compared them with the experimental results. The measured pressure values are well matched with the theoretical results. This indicates that the CPP can be used to reliably measure the pressure of fluid flows in a tube. As a result, when the flow rate increases 200 times, the increasing rate (slope) of pressure increases 25.9 times and the hydraulic resistance increases by 27.5% as the number n increases 1 to 3. In addition, as the distance between two membranes increases more than 6 cm, the flow pressure of the flow passing the two membranes approaches the value for passing a single membrane. This study will be helpful to understand the pressure variations in various porous fluidic systems composed of membranes.

Three-dimensional flow velocity and wall shear stress distribution measurement on a micropillar-arrayed surface using astigmatism PTV to understand the influence of microstructures on the flow field

In this study, the influence of the microstructure in a microchannel on the three-dimensional (3D) flow field and shear stress distribution on the wall was investigated with 3D velocity measurement method. In a micro-total analysis system or a lab-on-a-chip application, the control of the flow is necessary. Thus, microstructures are often applied to the fluidic system for passive flow control. However, the flow field which interacts with microstructures becomes complicated three-dimensionally. The 3D measurement of such microfluidic flow would give insight on the interaction of the flow with the structures and be also useful for other applications. In this study, micropillar array was introduced in a microchannel and we investigated the influence of the micropillar on the 3D flow field by the astigmatism particle tracking velocimetry which enables to determine three-dimensional and three-component velocity by single-viewing. Furthermore, the wall shear stress distribution was also investigated. From measurement results, it was confirmed that the pillar changes the wall shear stress distribution and 3D velocity distribution. Compared to a flat channel (no-pillar array), the wall shear stress in our channel varied spatially in a range of approximately − 80 to + 20%. Moreover, we also conducted a numerical simulation to consolidate the measurement results.

Streaming potential analysis and electrokinetic energy conversion efficiency of two immiscible fluids in a nanochannel

In order to conduct extensive investigation of electrokinetic energy conversion in nanofluidic devices, the analysis of streaming potential of pressure driven flow in the two-layer fluidic system through a nanochannel is investigated theoretically. Under the influences of the interfacial electric potential difference and the interface charge density jump, we first obtain the analytical electric potential distribution in the present two-layer fluidic system with consideration of Debye–Hückel linearization assumption. Then the analytical expressions of streaming potential field and flow velocity are derived. Based on the obtained the streaming potential, we finally give the analytical electrokinetic energy conversion efficiency in two-layer fluidic system and discuss the influences of related physical parameters on it. The theoretical result shows that the streaming potential can be viewed as a criterion to estimate the electrokinetic energy conversion efficiency. The electrokinetic energy conversion efficiency can be enhanced by the viscosity ratio and the interfacial slip length, but be restrained by the permittivity ratio and ion friction coefficient. Comparing to the single-layer fluidic system, the electrokinetic energy conversion efficiency can be augmented obviously in the two-layer fluidic system by selecting optimized flow parameters.