Improving hydrodynamic injection in capillary electrophoresis by using the integral of pressure

A careful analysis of the typical devices and conditions used during hydrodynamic injection in capillary electrophoresis shows that the Hagen-Poiseuille model for the laminar flow is valid, even during the transitions of pressure. Therefore, the monitoring of pressure becomes a reliable approach to evaluate the effective injected volume, because the volume is proportional to the integral of pressure (IoP) over time. A piezoresistive sensor was used to monitor the air pressure at headspace of the sample vial. A set of 18 injections at 50 mbar and different times were used to evaluate the use of the normalization of the peak areas of the analytes by the IoP to compensate for imperfection during the injection. There was a significant decrease in relative standard deviation (RSD), and the proposed approach presented results similar to the use of internal standard. In addition, a microcontroller was used not only to monitor the pressure but also to command a peristaltic pump and a solenoid valve creating a system that dynamically controls the applied pressure and stops the injection when the desired value of IoP is reached. The system was used in a proof of concept in which different combinations of pressure and time were used: 10 mbar × 50 s, 25 mbar × 20 s, 50 mbar × 10 s, 125 mbar × 4 s, and 250 mbar × 2 s. Despite the constraints posed by the flowrates of the peristaltic pump and the solenoid valve, the microcontroller effectively conducted the injections across this extensive range of conditions, resulting in an IoP RSD of 2.7%.

Microfluidic Mixing: A Physics-Oriented Review

This comprehensive review paper focuses on the intricate physics of microfluidics and their application in micromixing techniques. Various methods for enhancing mixing in microchannels are explored, with a keen emphasis on the underlying fluid dynamics principles. Geometrical micromixers employ complex channel designs to induce fluid-fluid interface distortions, yielding efficient mixing while retaining manufacturing simplicity. These methods synergize effectively with external techniques, showcasing promising potential. Electrohydrodynamics harnesses electrokinetic phenomena like electroosmosis, electrophoresis, and electrothermal effects. These methods offer dynamic control over mixing parameters via applied voltage, frequency, and electrode positioning, although power consumption and heating can be drawbacks. Acoustofluidics leverages acoustic waves to drive microstreaming, offering localized yet far-reaching effects. Magnetohydrodynamics, though limited in applicability to certain fluids, showcases potential by utilizing magnetic fields to propel mixing. Selecting an approach hinges on trade-offs among complexity, efficiency, and compatibility with fluid properties. Understanding the physics of fluid behavior and rationalizing these techniques aids in tailoring the most suitable micromixing solution. In a rapidly advancing field, this paper provides a consolidated understanding of these techniques, facilitating the informed choice of approach for specific microfluidic mixing needs.

Investigation of Hydrothermal Performance in Micro-Channel Heat Sink with Periodic Rectangular Fins

The micro-channel heat sink (MCHS) is an excellent choice due to its exceptional cooling capabilities, surpassing those of its competitors. In this research paper, a computational fluid dynamics analysis was performed to investigate the laminar flow and heat transfer characteristics of five different configurations of a variable geometry rectangular fin. The study utilized a water-cooled smooth MCHS as the basis. The results indicate that the micro-channel heat sink with a variable geometry rectangular fin has better heat dissipation capacity than a straight-type micro-channel heat sink, but at the same time, it has larger pressure loss. Based on the analysis of various rectangular fin shapes and Reynolds numbers in this study, the micro-channel heat sink with rectangular fins exhibits Nusselt numbers and friction factors that are 1.40-2.02 and 2.64-4.33 times higher, respectively, compared to the smooth heat sink. This significant improvement in performance results in performance evaluation criteria ranging from 1.23-1.95. Further, it is found that at a relatively small Reynolds number, the micro-channel heat sink with a variable geometry rectangular fin has obvious advantages in terms of overall cooling performance. Meanwhile, this advantage will decrease when the Reynolds number is relatively large.

Endothelial activation and fibrotic changes are impeded by laminar flow-induced CHK1-SENP2 activity through mechanisms distinct from endothelial-to-mesenchymal cell transition

Background

The deSUMOylase sentrin-specific isopeptidase 2 (SENP2) plays a crucial role in atheroprotection. However, the phosphorylation of SENP2 at T368 under disturbed flow (D-flow) conditions hinders its nuclear function and promotes endothelial cell (EC) activation. SUMOylation has been implicated in D-flow-induced endothelial-to-mesenchymal transition (endoMT), but the precise role of SENP2 in counteracting this process remains unclear.

Method

We developed a phospho-specific SENP2 S344 antibody and generated knock-in (KI) mice with a phospho-site mutation of SENP2 S344A using CRISPR/Cas9 technology. We then investigated the effects of SENP2 S344 phosphorylation under two distinct flow patterns and during hypercholesteremia (HC)-mediated EC activation.

Result

Our findings demonstrate that laminar flow (L-flow) induces phosphorylation of SENP2 at S344 through the activation of checkpoint kinase 1 (CHK1), leading to the inhibition of ERK5 and p53 SUMOylation and subsequent suppression of EC activation. We observed a significant increase in lipid-laden lesions in both the aortic arch (under D-flow) and descending aorta (under L-flow) of female hypercholesterolemic SENP2 S344A KI mice. In male hypercholesterolemic SENP2 S344A KI mice, larger lipid-laden lesions were only observed in the aortic arch area, suggesting a weaker HC-mediated atherogenesis in male mice compared to females. Ionizing radiation (IR) reduced CHK1 expression and SENP2 S344 phosphorylation, attenuating the pro-atherosclerotic effects observed in female SENP2 S344A KI mice after bone marrow transplantation (BMT), particularly in L-flow areas. The phospho-site mutation SENP2 S344A upregulates processes associated with EC activation, including inflammation, migration, and proliferation. Additionally, fibrotic changes and up-regulated expression of EC marker genes were observed. Apoptosis was augmented in ECs derived from the lungs of SENP2 S344A KI mice, primarily through the inhibition of ERK5-mediated expression of DNA damage-induced apoptosis suppressor (DDIAS).

Summary

In this study, we have revealed a novel mechanism underlying the suppressive effects of L-flow on EC inflammation, migration, proliferation, apoptosis, and fibrotic changes through promoting CHK1-induced SENP2 S344 phosphorylation. The phospho-site mutation SENP2 S344A responds to L-flow through a distinct mechanism, which involves the upregulation of both mesenchymal and EC marker genes.

Microfluidic-Based Continuous Fabrication of Ultrathin Hydrogel Films with Controllable Thickness

Ultrathin hydrogel films composed of cross-linked polymer networks swollen by water, with soft and moisturized features similar to biological tissue, play a vital role in flexible biosensors and wearable electronics. However, achieving efficient and continuous fabrication of such films remains a challenge. Here, we present a microfluidic-based strategy for the continuous fabrication of free-standing ultrathin hydrogel films by using laminar flow, which can be precisely controlled in the micrometer scale. Compared with conventional methods, the microfluidic-based method shows advantages in producing hydrogel films with a high homogeneity as well as maintaining the structural integrity, without the need of supporting substrates and sophisticated equipment. This strategy allows the precise control over the thickness of the hydrogel films ranging from 15 ± 0.2 to 39 ± 0.5 μm, by adjusting the height of the microfluidic channels, with predictable opportunities for scaling up. Therefore, our strategy provides a facile route to produce advanced thin polymer films in a universal, steerable, and scalable manner and will promote the applications of thin polymer films in biosensors and wearable electronics.

Effect of Flow Velocity on Laminar Flow in Microfluidic Chips

Gel fibers prepared based on microfluidic laminar flow technology have important research value in constructing biomimetic scaffolds and tissue engineering. The key point of microfluidic laminar flow technology is to find the appropriate fluid flow rate in the micropipe. In order to explore the influence of flow rate on the laminar flow phenomenon of a microfluidic chip, a microfluidic chip composed of an intermediate main pipe and three surrounding outer pipes are designed, and the chip is prepared by photolithography and the composite molding method. Then, a syringe pump is used to inject different fluids into the microtubing, and the data of fluid motion are obtained through fluid dynamics simulation and finite element analysis. Finally, a series of optimal adjustments are made for different fluid composition and flow rate combinations to achieve the fluid's stable laminar flow state. It was determined that when the concentration of sodium alginate in the outer phase was 1 wt% and the concentration of CaCl₂ in the inner phase was 0.1 wt%, the gel fiber prepared was in good shape, the flow rate was the most stable, and laminar flow was the most obvious when the flow rate of both was 1 mL/h. This study represents a preliminary achievement in exploring the laminar flow rate and fabricating gel fibers, thus offering significant reference value for investigating microfluidic laminar flow technology.

Identification and validation of G protein-coupled receptors modulating flow-dependent signaling pathways in vascular endothelial cells

Vascular endothelial cells are exposed to mechanical forces due to their presence at the interface between the vessel wall and flowing blood. The patterns of these mechanical forces (laminar vs. turbulent) regulate endothelial cell function and play an important role in determining endothelial phenotype and ultimately cardiovascular health. One of the key transcriptional mediators of the positive effects of laminar flow patterns on endothelial cell phenotype is the zinc-finger transcription factor, krüppel-like factor 2 (KLF2). Given its importance in maintaining a healthy endothelium, we sought to identify endothelial regulators of the KLF2 transcriptional program as potential new therapeutic approaches to treating cardiovascular disease. Using an approach that utilized both bioinformatics and targeted gene knockdown, we identified endothelial GPCRs capable of modulating KLF2 expression. Genetic screening using siRNAs directed to these GPCRs identified 12 potential GPCR targets that could modulate the KLF2 program, including a subset capable of regulating flow-induced KLF2 expression in primary endothelial cells. Among these targets, we describe the ability of several GPCRs (GPR116, SSTR3, GPR101, LGR4) to affect KLF2 transcriptional activation. We also identify these targets as potential validated targets for the development of novel treatments targeting the endothelium. Finally, we highlight the initiation of drug discovery efforts for LGR4 and report the identification of the first known synthetic ligands to this receptor as a proof-of-concept for pathway-directed phenotypic screening to identify novel drug targets.

Intraoperative mydriasis in left ventricular assist device patients. Do eyes never lie?

We report two cases of transient intraoperative mydriasis in left ventricular assist device (LVAD) patients with no profound underlining neurological pathology. Both cases concern females on LVAD for more than 30 months, due to dilated cardiomyopathy, as a bridge to transplant. A possible pathophysiology mechanism is suggested. As LVAD patients' life expectancy increases, more and more physiological alterations due to laminar flow will be revealed and must be taken into consideration for the better care of this patient group.

Surface Cleanliness Maintenance with Laminar Flow Based on the Characteristics of Laser-Induced Sputtering Particles in High-Power Laser Systems

In high-power laser systems, the primary cause of contamination of optical components and degradation of spatial cleanliness is laser-induced sputtering of particles. To mitigate this problem, laminar flow is frequently utilized to control the direction and transport of these particles. This study characterizes the properties of laser-induced sputtering particles, including their flying trend, diameter range, and velocity distribution at varying time intervals. A time-resolved imaging method was employed to damage the rear surface of fused silica using a 355 nm Nd: YAG pump laser. The efficacy of laminar flow in controlling these particles was then assessed, with a particular focus on the influence of laminar flow direction, laminar flow velocity, particle flight height, and particle diameter. Our results indicate that the optimal laminar flow velocity for preventing particle invasion is highly dependent on the maximum particle attenuation distance (or safety distance), which can vary by up to two orders of magnitude. Furthermore, a laminar flow velocity of 0.5 m/s can effectively prevent particle sedimentation. Future research will aim to optimize laminar flow systems based on these findings to achieve high surface cleanliness in high-power laser systems with minimal energy consumption.

Shear stress control of vascular leaks and atheromas through Tie2 activation by VE-PTP sequestration

Vascular endothelial protein tyrosine phosphatase (VE-PTP) influences endothelial barrier function by regulating the activation of tyrosine kinase receptor Tie2. We determined whether this action is linked to the development of atherosclerosis by examining the influence of arterial shear stress on VE-PTP, Tie2 activation, plasma leakage, and atherogenesis. We found that exposure to high average shear stress led to downstream polarization and endocytosis of VE-PTP accompanied by Tie2 activation at cell junctions. In aortic regions with disturbed flow, VE-PTP was not redistributed away from Tie2. Endothelial cells exposed to high shear stress had greater Tie2 activation and less macromolecular permeability than regions with disturbed flow. Deleting endothelial VE-PTP in VE-PTP^iECKO mice increased Tie2 activation and reduced plasma leakage in atheroprone regions. ApoE^-/- mice bred with VE-PTP^iECKO mice had less plasma leakage and fewer atheromas on a high-fat diet. Pharmacologic inhibition of VE-PTP by AKB-9785 had similar anti-atherogenic effects. Together, the findings identify VE-PTP as a novel target for suppression of atherosclerosis.

An Approximate Method for Predicting the Friction Factor of Viscoplastic Shear-Thinning Fluids in Non-Circular Channels of Regular Cross-Sections

The objective of this study is to provide a straightforward generalized simple and quick method for the prediction of the friction factor for fully developed laminar flow of viscoplastic shear-thinning fluids in non-circular channels of regular cross-sections. The most frequently represented substances processed under these conditions are polymers in the processing and plastics industry. A generalized approximate method was proposed to express the relationship between the friction factor and the Reynolds number for the Herschel-Bulkley rheological model. This method uses the generalized Reynolds number for power-law fluids. Moreover, an additional simplified method for rapid engineering calculations was obtained as well. The suggested method was verified by comparing experimental data for concentric annulus found in the literature and results from simulations for concentric annulus, rectangular, square duct with a central cylindrical core and elliptical cross-sections. The results showed that the suggested methods enable us to estimate the friction factor with high accuracy for the investigated geometries.

Real-Time Tunable Optofluidic Splitter via Two Laminar Flow Streams in a Microchannel

This paper reports a tunable optofluidic splitter in which the incident light is split via refraction and reflection at the interface between two laminar flows in a microchannel but with different refractive indices. A Y-junction microchannel is used to demonstrate the continuous tuning of the splitting ratio of optical power by smooth adjustment of the ratio of two flow rates. In addition, it has achieved the tuning of split angle from 5° to 19° by the control of the refractive index contrast. The dynamic response gives a fastest switching frequency of 1.67 Hz between the "wave-guiding" and "splitting" status.

3D Numerical Simulation and Structural Optimization for a MEMS Skin Friction Sensor in Hypersonic Flow

The skin friction of a hypersonic vehicle surface can account for up to 50% of the total resistance, directly affecting the vehicle's effective range and load. A wind tunnel experiment is an important and effective method to optimize the aerodynamic shape of aircraft, and Micro-Electromechanical System (MEMS) skin friction sensors are considered the promising sensors in hypersonic wind tunnel experiments, owing to their miniature size, high sensitivity, and stability. However, the sensitive structure including structural appearance, a gap with the package shell, and flatness of the sensor will change the measured flow field and cause the accurate measurement of friction resistance. Aiming at the influence of sensor-sensitive structure on wall-flow characteristics and friction measurement accuracy, the two-dimensional and three-dimensional numerical models of the sensor in the hypersonic flow field based on Computational Fluid Dynamics (CFD) are presented respectively in this work. The model of the sensor is verified by using the Blathius solution of two-dimensional laminar flow on a flat plate. The results show that the sensor model is in good agreement with the Blathius solution, and the error is less than 0.4%. Then, the influence rules of the sensitive structure of the sensor on friction measurement accuracy under turbulent flow and laminar flow conditions are systematically analyzed using 3D numerical models of the sensor, respectively. Finally, the sensor-sensitive unit structure's design criterion is obtained to improve skin friction's measurement accuracy.

Peristaltic pumps adapted for laminar flow experiments enhance in vitro modeling of vascular cell behavior

Endothelial cells (ECs) are the primary cellular constituent of blood vessels that are in direct contact with hemodynamic forces over their lifetime. Throughout the body, vessels experience different blood flow patterns and rates that alter vascular architecture and cellular behavior. Because of the complexities of studying blood flow in an intact organism, particularly during development, the field has increasingly relied on in vitro modeling of blood flow as a powerful technique for studying hemodynamic-dependent signaling mechanisms in ECs. While commercial flow systems that recirculate fluids exist, many commercially available pumps are peristaltic and best model pulsatile flow conditions. However, there are many important situations in which ECs experience laminar flow conditions in vivo, such as along long straight stretches of the vasculature. To understand EC function under these contexts, it is important to be able to reproducibly model laminar flow conditions in vitro. Here, we outline a method to reliably adapt commercially available peristaltic pumps to study laminar flow conditions. Our proof-of-concept study focuses on 2D models but could be further adapted to 3D environments to better model in vivo scenarios, such as organ development. Our studies make significant inroads into solving technical challenges associated with flow modeling and allow us to conduct functional studies toward understanding the mechanistic role of shear forces on vascular architecture, cellular behavior, and remodeling in diverse physiological contexts.

Analytical Solutions for Simple Turbulent Shear Flows on a Basis of a Generalized Newton's Law

In the presented article a generalization of Newton's formula for the shear stress in a fluid is carried out by giving it a power-law form. After the introduction of the corresponding strain rate tensor, a generalization is made to the spatial case of flow and the rheological relation is presented in tensor form. Depending on the power value in this rheological ratio, one can come either to a description of a laminar flow regime (in the form of Navier-Stokes equations), or to a description of the flow in turbulent regime. In the latter case, a set of differential equations with the no-slip boundary condition is specified, which is significantly different from that for the laminar flow regime, but which also allows one to obtain analytical solutions for simple shear flows and obtain the Blasius resistance law for the flow in a pipe. Therefore, the considered approach to solving problems of turbulent flows compares favorably with modern differential turbulence models. Solutions are given for simple shear flows of a fluid, when there is only one longitudinal component of the velocity, which depends on the transversal coordinate only. These solutions in terms of velocity profiles and resistance coefficients are in satisfactory agreement with the experimental data.

Compatibility and Validation of a Recent Developed Artificial Blood through the Vascular Phantom Using Doppler Ultrasound Color- and Motion-mode Techniques

Background:

Doppler technique is a technology that can raise the predictive, diagnostic, and monitoring abilities in blood flow and suitable for researchers. The application depends on Doppler shift (shift frequencies), wherein the movement of red blood cells away from the probe is determined by the decrease or increase in the ultrasound (US) frequency.

Methods:

In this experiment, the clinical US (Hitachi Avious [HI] model) system was used as a primary instrument for data acquisition and test the compatibility, efficacy, and validation of artificial blood (blood-mimicking fluid [BMF]) by color- and motion-mode. This BMF was prepared for use in the Doppler flow phantom.

Results:

The motion of BMF through the vessel-mimicking material (VMM) was parallel and the flow was laminar and in the straight form (regular flow of BMF inside the VMM). Moreover, the scale of color velocity in the normal range at that flow rate was in the normal range.

Conclusion:

The new BMF that is being valid and effective in utilizing for US in vitro research applications. In addition, the clinical US ([HI] model) system can be used as a suitable instrument for data acquisition and test the compatibility, efficacy, and validation at in vitro applications (BMF, flow phantom components).

Numerical Simulation and Experimental Investigation of Laser Ablation of Al2O3 Ceramic Coating

This paper presents an evaluation of the molten pool laser damage done to an Al₂O₃ ceramic coating. Mechanism analysis of the laser damage allowed for a 2D finite element model of laser ablation of the Al₂O₃ ceramic coating to be built. It consisted of heat transfer, laminar flow, and a solid mechanics module with the level set method. Results showed that the laser damage mechanisms through laser ablation were melting, gasification, spattering, and micro-cracking. The ablation depth and diameter increased with the increasing laser ablation time under continuous irradiation. The simulation profile was consistent with the experimental one. Additionally, the stress produced by the laser ablation was 3500–9000 MPa, which exceeded the tensile stress (350–500 MPa), and fracturing and micro-cracks occurred. Laser damage analysis was performed via COMSOL Multiphysics to predict laser damage morphology, and validate the 3D surface profiler and scanning electron microscope results.

Laminar Flow-Based Fiber Fabrication and Encoding via Two-Photon Lithography

In recent years, flow photolithography (FL) has emerged as a powerful synthetic tool for the creation of barcoded microparticles with complex morphologies and chemical compositions which have been shown to be useful in a range of multiplexed bioassay applications. More specifically, FL has been highly successful in producing micron-sized, encoded particles of bespoke shape, size, and color. That said, to date, FL has been restricted to generating barcoded microparticles and has lacked the ability to produce hybrid fibers which are structurally and spectrally encoded. To this end, we herein present a method that combines a continuous flow microfluidic system with two-photon polymerization (2PP) to fabricate microscale-encoded fibers and Janus strips in a high-throughput manner. Specifically, two co-flow liquid streams containing a monomer and initiator are introduced through a Y-shape channel to form a stable interface in the center of a microfluidic channel. The flow containing the (fluorescently labeled) monomer is then patterned by scanning the voxel of the 2PP laser across the interface to selectively polymerize different regions of the forming fiber/particle. Such a process allows for rapid spectral encoding at the single fiber level, with the resulting structurally coded fibers having obvious application in the fields of security identification and anticounterfeiting.

Calciprotein Particles Cause Endothelial Dysfunction under Flow

Calciprotein particles (CPPs), which increasingly arise in the circulation during the disorders of mineral homeostasis, represent a double-edged sword protecting the human organism from extraskeletal calcification but potentially causing endothelial dysfunction. Existing models, however, failed to demonstrate the detrimental action of CPPs on endothelial cells (ECs) under flow. Here, we applied a flow culture system, where human arterial ECs were co-incubated with CPPs for 4 h, and a normolipidemic and normotensive rat model (10 daily intravenous injections of CPPs) to simulate the scenario occurring in vivo in the absence of confounding cardiovascular risk factors. Pathogenic effects of CPPs were investigated by RT-qPCR and Western blotting profiling of the endothelial lysate. CPPs were internalised within 1 h of circulation, inducing adhesion of peripheral blood mononuclear cells to ECs. Molecular profiling revealed that CPPs stimulated the expression of pro-inflammatory cell adhesion molecules VCAM1 and ICAM1 and upregulated transcription factors of endothelial-to-mesenchymal transition (Snail, Slug and Twist1). Furthermore, exposure to CPPs reduced the production of atheroprotective transcription factors KLF2 and KLF4 and led to YAP1 hypophosphorylation, potentially disturbing the mechanisms responsible for the proper endothelial mechanotransduction. Taken together, our results suggest the ability of CPPs to initiate endothelial dysfunction at physiological flow conditions.

Studying the Impact of Wall Shear Stress on the Development and Performance of Electrochemically Active Biofilms

A laminar flow reactor was designed that provides constant and reproducible growth conditions for the bioelectrochemical observation of electroactive bacteria (EAB). Experiments were performed using four reactors in parallel to enable the comparison of EAB growth behavior and bioelectrochemical performance under different hydrodynamic conditions while simultaneously keeping biological conditions identical. With regard to the moderate flow conditions found in wastewater treatment applications, the wall shear stress was adjusted to a range between 0.4 mPa to 2.9 mPa. Chronoamperometric data indicate that early stage current densities are improved by a moderate increase of the wall shear stress. In the same way, current onset times were increasing slightly towards higher values of the applied wall shear stress. Long-term observations of EAB performance showed a decrease in current density and a leveling of the trend observed for the early stages of biofilm growth.

Investigation of Heat Transfer and Pressure Drop in Microchannel Heat Sink Using Al2O3 and ZrO2 Nanofluids

A new micro heat exchanger was analyzed using numerical formulation of conjugate heat transfer for single-phase fluid flow across copper microchannels. The flow across bent channels harnesses asymmetric laminar flow and dean vortices phenomena for heat transfer enhancement. The single-channel analysis was performed to select the bent channel aspect ratio by varying width and height between 35–300 μm for Reynolds number and base temperature magnitude range of 100–1000 and 320–370 K, respectively. The bent channel results demonstrate dean vortices phenomenon at the bend for Reynolds number of 500 and above. Thermal performance factor analysis shows an increase of 18% in comparison to straight channels of 200 μm width and height. Alumina nanoparticles at 1% and 3% concentration enhance the Nusselt number by an average of 10.4% and 23.7%, respectively, whereas zirconia enhances Nusselt number by 16% and 33.9% for same concentrations. On the other hand, thermal performance factor analysis shows a significant increase in pressure drop at high Reynolds number with 3% particle concentration. Using zirconia for nanofluid, Nusselt number of the bent multi-channel model is improved by an average of 18% for a 3% particle concentration as compared to bent channel with deionized water.

Microflow system promotes acetaminophen crystal nucleation

It is known that interfaces have various impacts on crystallization from a solution. Here, we describe crystallization of acetaminophen using a microflow channel, in which two liquids meet and form a liquid-liquid interface due to laminar flow, resulting in uniform mixing of solvents on the molecular scale. In the anti-solvent method, the microflow mixing promoted the crystallization more than bulk mixing. Furthermore, increased flow rate encouraged crystal formation, and a metastable form appeared under a certain flow condition. This means that interface management by the microchannel could be a beneficial tool for crystallization and polymorph control.

Impact of Wind Speed on Response of Diffusion-Type Radon-Thoron Detectors to Thoron

Air exchange through a porous medium depends partly on a pressure gradient induced in it, i.e., air-flow conditions of the outer air. Consequently, response of diffusion-type detectors to radon and thoron may vary with air-flow conditions surrounding the detectors. This effect may be significant for thoron measurement because thoron has a shorter half-life than radon. The present study examined response of diffusion-type detectors (RADUETs and one AlphaGUARD) to thoron with respect to wind speed using a thoron calibration chamber. Response of RADUETs to thoron increased with wind speed. Response of the AlphaGUARD increased with wind speed, but it became constant at a high wind speed. Different response trends to thoron between the RADUETs and the AlphaGUARD could be qualitatively explained by flow states induced by the pressure gradient in the filter or the sponge of these detectors. For RADUETs, laminar (Darcy) flow was induced in the sponge in the examined wind speed range, which meant that thoron entry into the detector increased with wind speed. For the AlphaGUARD, laminar flow was induced in the filter in the low wind speed range, whereas flow was changed to turbulent (non-Darcy) flow at a high wind speed for which thoron entry into the detector did not depend on wind speed.

Aseptic Technique

This article describes common laboratory procedures that can reduce the risk of culture contamination (sepsis), collectively referred as "aseptic technique." Two major strategies for aseptic work are described: using a Bunsen burner and using a laminar flow hood. Both methods are presented in the form of general protocols applicable to a variety of laboratory tasks such as pipetting and dispensing aliquots, preparing growth media, and inoculating, passaging, and spreading microorganisms on petri dishes. © 2020 by John Wiley & Sons, Inc.

Fritz Rohrer (1888-1926), a pioneer in pulmonary mechanics whose work was inexplicably ignored for about 30 years

Fritz Rohrer (1888-1926) has a special place in the history of respiratory physiology for two reasons. The first is that he laid the foundations of modern pulmonary mechanics in the early 1900s. For example, his seminal paper on pulmonary dynamics, that is, the pressure-flow relationships in the airways, was published in 1915 in one of the top journals in the field. It included extensive measurements of airway dimensions in postmortem human lungs and a sophisticated analysis of the modes of airflow. This was closely followed by a very original analysis of lung statics, which included studies of airway pressures at normal, maximal, and minimal lung volumes in relaxed normal volunteers, and was published in 1916. Remarkably, both papers were essentially ignored at the time. Fortunately, in 1925 he was able to summarize his major findings in a chapter in an important handbook of physiology. However, he tragically died from pulmonary tuberculosis in the following year at the early age of 37. The second reason for his importance in the history of pulmonary mechanics is that inexplicably his very innovative research was essentially ignored for about 30 years. It was not until the 1940s that his work was rediscovered, although not in time to save investigators from duplicating his very original studies. Possible reasons why his work was ignored for so long are discussed. Even today it is not easy to recover some important features of his career, and some aspects of his very original research are still almost unknown.

Physiological and Microscopic Characterization of Cyclic-di-GMP-Mediated Autoaggregation in Erwinia amylovora

The second messenger cyclic-di-GMP (c-di-GMP) is a critical regulator of biofilm formation in the plant pathogen Erwinia amylovora. Phosphodiesterase (PDE) enzymes are responsible for the degradation of intracellular c-di-GMP. Previously, we found that the deletion of one or more of the three PDE enzyme encoding genes (pdeA, pdeB, and pdeC) in E. amylovora Ea1189 led to an increase in biofilm formation. However, in mutants Ea1189ΔpdeAC and Ea1189ΔpdeABC, biofilm formation was reduced compared to the other single and double deletion mutants. Here, we attribute this to an autoaggregation phenotype observed in these two mutants. Examination of Ea1189ΔpdeABC cellular aggregates using scanning electron microscopy indicated that a subset of cells were impaired in cell separation post cell division. Concomitant with this phenotype, Ea1189ΔpdeABC also exhibited increased transcription of the cell-division inhibitor gene sulA and reduced transcription of ftsZ. Ea1189ΔpdeABC showed a significant reduction in biofilm formation, and biofilms formed by Ea1189ΔpdeABC exhibited a distinctive morphology of sparsely scattered aggregates rather than an evenly distributed biofilm as observed in WT Ea1189. Our results suggest that highly elevated levels of c-di-GMP lead to increased cell-cell interactions that contribute to autoaggregation and impair cell-surface interaction, negatively affecting biofilm formation.

Fast Start-Up Microfluidic Microbial Fuel Cells With Serpentine Microchannel

Microfluidic microbial fuel cells (MMFCs) are promising green power sources for future ultra-small electronic devices. The MMFCs with co-laminar microfluidic structure are superior to other MMFCs according to their low internal resistance and relative high power density. However, the area for interfacial electron transfer between the bacteria and the anode is quite limited in the typical Y-shaped device, which apparently restricts the current generation performance. In this study, we developed a membraneless MMFC with serpentine microchannel to enhance the interfacial electron transfer and promote the power generation of the device. Owing to the merit of laminar flow, the proposed MMFC was working well without any proton exchange membrane (PEM). At the same time, the serpentine microchannel greatly increased the power density. The S-MMFC catalyzed by Shewanella putrefaciens CN32 achieves a peak power density of 360 mW/m² with the optimal channel configuration and the flow rate of 5 ml/h. Meanwhile, this device possesses much shorter start-up time and much longer duration time at high current plateau than the previous reported MMFCs. The presented MMFC appears promising for biochip technology and extends the scope of microfluidic energy.

Macromolecule Orientation in Nanofibers

Electrospinning is now commercially used for the fabrication of nano/micro fibers. Compared with spider dragline silk, artificial fibers have poor mechanical properties. Unlike natural silk, which has a hierarchical structure with an approximate 3-fold symmetry, the molecular structure of spun fiber has neither folding nor orientation. To date, it is almost impossible to control molecule orientation during the spinning process. Here, we show that macromolecule orientation can be easily controlled using the laminar flow of fluid mechanics. A lasting laminar flow in a long needle can order macromolecules. We find that the orientation of macromolecules can greatly affect the morphology and mechanical properties of fibers. We expect our technology to be helpful for more sophisticated fabrication of fibers with ordered macromolecules and DNA-like twists.

The Impact of Patient and Surgical Factors on the Rate of Postoperative Infection After Total Hip Arthroplasty-A New Zealand Joint Registry Study

BACKGROUND

Periprosthetic joint infection (PJI) is a devastating complication after total hip arthroplasty (THA). The potential to define and modify risk factors for infection represents an important opportunity to reduce the incidence of PJI. This study uses New Zealand Joint Registry data to identify independent risk factors associated with PJI after primary THA.

METHODS

Data on 91,585 THAs performed between 2000 and 2014 were analyzed. Factors associated with revision for PJI within 12 months were identified using univariate and multivariate analyses.

RESULTS

Revision rates for PJI were 0.15% and 0.21% at 6 and 12 months, respectively. Multivariate analysis showed significant associations with the American Society of Anesthesiologists grade (odds ratio [OR] 6.13, 95% confidence interval [CI] 1.28-29.39), severe or morbid obesity (OR 2.15, CI 1.01-4.60 and OR 3.73, CI 1.49-9.39), laminar flow ventilation (OR 1.98, CI 1.38-2.85), consultant-supervised trainee operations (OR 1.94, CI 1.22-3.08), male gender (OR 1.68, CI 1.23-2.30) and anterolateral approach (OR 1.62, CI 1.11-2.37). Procedures performed in the private sector were protective for revision for infection (OR 0.68, CI 0.48-0.96).

CONCLUSIONS

The PJI risk profile for patients undergoing THA is constituted of a complex of patient and surgical factors. Several patient factors had strong independent associations with revision rates for PJI. Although surgical factors were less important, these may be more readily modifiable in practice.

Gas Flow in the Capillary of the Atmosphere-to-Vacuum Interface of Mass Spectrometers

Numerical simulations of a gas flow through a capillary being a part of mass spectrometer atmospheric interface were performed using a detailed laminar flow model. The simulated interface consisted of atmospheric and forevacuum volumes connected via a thin capillary. The pressure in the forevacuum volume where the gas was expanding after passing through the capillary was varied in the wide range from 10 to 900 mbar in order to study the volume flow rate as well as the other flow parameters as functions of the pressure drop between the atmospheric and forevacuum volumes. The capillary wall temperature was varied in the range from 24 to 150 °C. Numerical integration of the complete system of Navier-Stokes equations for a viscous compressible gas taking into account the heat transfer was performed using the standard gas dynamic simulation software package ANSYS CFX. The simulation results were compared with experimental measurements of gas flow parameters both performed using our experimental setup and taken from the literature. The simulated volume flow rates through the capillary differed no more than by 10% from the measured ones over the entire pressure and temperatures ranges. A conclusion was drawn that the detailed digital laminar model is able to quantitatively describe the measured gas flow rates through the capillaries under conditions considered. Graphical Abstract ᅟ.

Microfluidic accumulation assay probes attachment of biofilm forming diatom cells

Testing of fouling release (FR) technologies is of great relevance for discovery of the next generation of protective marine coatings. In this paper, an accumulation assay to test diatom interaction under laminar flow with the model organism Navicula perminuta is introduced. Using time lapse microscopy with large area sampling allows determination of the accumulation kinetics of the diatom on three model surfaces with different surface properties at different wall shear stresses. The hydrodynamic conditions within the flow cell are described and a suitable shear stress range to perform accumulation experiments is identified at which statistically significant discrimination of surfaces is possible. The observed trends compare well to published adhesion preferences of N. perminuta. Also, previously determined trends of critical wall shear stresses required for cell removal from the same set of functionalized interfaces shows consistent trends. Initial attachment mediated by extracellular polymeric substances (EPS) present outside the diatoms leads to the conclusion that the FR potential of the tested coating candidates can be deducted from dynamic accumulation experiments under well-defined hydrodynamic conditions. As well as testing new coating candidates for their FR properties, monitoring of the adhesion process under flow provides additional information on the mechanism and geometry of attachment and the population kinetics.

A parametric model of the brain vascular system for estimation of the arterial input function (AIF) at the tissue level

In this paper, we introduce a novel model of the brain vascular system, which is developed based on laws of fluid dynamics and vascular morphology. This model is used to address dispersion and delay of the arterial input function (AIF) at different levels of the vascular structure and to estimate the local AIF in DCE images. We developed a method based on the simplex algorithm and Akaike information criterion to estimate the likelihood of the contrast agent concentration signal sampled in DCE images belonging to different layers of the vascular tree or being a combination of different signal levels from different nodes of this structure. To evaluate this method, we tested the method on simulated local AIF signals at different levels of this structure. Even down to a signal to noise ratio of 5.5 our method was able to accurately detect the branching level of the simulated signals. When two signals with the same power level were combined, our method was able to separate the base signals of the composite AIF at the 50% threshold. We applied this method to dynamic contrast enhanced computed tomography (DCE-CT) data, and using the parameters estimated by our method we created an arrival time map of the brain. Our model corrected AIF can be used for solving the pharmacokinetic equations for more accurate estimation of vascular permeability parameters in DCE imaging studies.

Microfluidic Mixing and Analog On-Chip Concentration Control Using Fluidic Dielectrophoresis

Microfluidic platforms capable of complex on-chip processing and liquid handling enable a wide variety of sensing, cellular, and material-related applications across a spectrum of disciplines in engineering and biology. However, there is a general lack of available active microscale mixing methods capable of dynamically controlling on-chip solute concentrations in real-time. Hence, multiple microfluidic fluid handling steps are often needed for applications that require buffers at varying on-chip concentrations. Here, we present a novel electrokinetic method for actively mixing laminar fluids and controlling on-chip concentrations in microfluidic channels using fluidic dielectrophoresis. Using a microfluidic channel junction, we co-flow three electrolyte streams side-by-side so that two outer conductive streams enclose a low conductive central stream. The tri-laminar flow is driven through an array of electrodes where the outer streams are electrokinetically deflected and forced to mix with the central flow field. This newly mixed central flow is then sent continuously downstream to serve as a concentration boundary condition for a microfluidic gradient chamber. We demonstrate that by actively mixing the upstream fluids, a variable concentration gradient can be formed dynamically downstream with single a fixed inlet concentration. This novel mixing approach offers a useful method for producing variable on-chip concentrations from a single inlet source.

Microchemical Pen: An Open Microreactor for Region-Selective Surface Modification

Various micro surface-modification approaches including photolithography, dip-pen lithography and ink-jet systems have been developed and used to extend the functionalities of solid surfaces. While those approaches work in the "open space", push-pull systems which work in solutions have recently drawn considerable attention. However, the confining flows performed by push-pull systems have realized only the dispense process, while microscale, region-selective chemical reactions have remained unattainable. This study reports a microchemical pen that enables region-selective chemical reactions for the micro surface modification/patterning. The chemical pen is based on the principle of microfluidic laminar flows and the resulting mixing of reagents by the mutual diffusion. The tiny diffusion layer performs as the working region. This report represents the first demonstration of an open microreactor in which two different reagents react on a real solid sample. The multifunctional characteristics of the microchemical pen are confirmed by different types of reactions in many research areas, including inorganic chemistry, polymer science, electrochemistry and biological sample treatment.

Atheroprotective laminar flow inhibits Hippo pathway effector YAP in endothelial cells

Atherosclerosis is a mechanobiology-related disease that preferentially develops in the aortic arch and arterial branches, which are exposed to disturbed/turbulent blood flow but less in thoracic aorta where the flow pattern is steady laminar flow (LF). Increasing evidence supports that steady LF with high shear stress is protective against atherosclerosis. However, the molecular mechanisms of LF-mediated atheroprotection remain incompletely understood. Hippo/YAP (yes-associated protein) pathway senses and effects mechanical cues and has been reported to be a master regulator of cell proliferation, differentiation, and tissue homeostasis. Here, we show that LF inhibits YAP activity in endothelial cells (ECs). We observed that YAP is highly expressed in mouse EC-enriched tissues (lung and aorta) and in human ECs. Furthermore, we found in apolipoprotein E deficient (ApoE(-/-)) mice and human ECs, LF decreased the level of nuclear YAP protein and YAP target gene expression (connective tissue growth factor and cysteine-rich protein 61) through promoting Hippo kinases LATS1/2-dependent YAP (Serine 127) phosphorylation. Functionally, we revealed that YAP depletion in ECs phenocopying LF responses, reduced the expression of cell cycle gene cyclin A1 (CCNA1) and proinflammatory gene CCL2 (MCP-1). Taken together, we demonstrate that atheroprotective LF inhibits endothelial YAP activation, which may contribute to LF-mediated ECs quiescence and anti-inflammation.

Decreased Pseudomonas aeruginosa biofilm formation on nanomodified endotracheal tubes: a dynamic lung model

Ventilator-associated pneumonia (VAP) is a serious complication of mechanical ventilation that has been shown to be associated with increased mortality rates and medical costs in the pediatric intensive care unit. Currently, there is no cost-effective solution to the problems posed by VAP. Endotracheal tubes (ETTs) that are resistant to bacterial colonization and that inhibit biofilm formation could provide a novel solution to the problems posed by VAP. The objective of this in vitro study was to evaluate differences in the growth of Pseudomonas aeruginosa on unmodified polyvinyl chloride (PVC) ETTs and on ETTs etched with a fungal lipase, Rhizopus arrhizus, to create nanoscale surface features. These differences were evaluated using an in vitro model of the pediatric airway to simulate a ventilated patient in the pediatric intensive care unit. Each experiment was run for 24 hours and was supported by computational models of the ETT. Dynamic conditions within the ETT had an impact on the location of bacterial growth within the tube. These conditions also quantitatively affected bacterial growth especially within the areas of tube curvature. Most importantly, experiments in the in vitro model revealed a 2.7 log reduction in the number (colony forming units/mL) of P. aeruginosa on the nanoroughened ETTs compared to the untreated PVC ETTs after 24 hours. This reduction in total colony forming units/mL along the x-axis of the tube was similar to previous studies completed for Staphylococcus aureus. Thus, this dynamic study showed that lipase etching can create surface features of nanoscale roughness on PVC ETTs that decrease bacterial attachment of P. aeruginosa without the use of antibiotics and may provide clinicians with an effective and inexpensive tool to combat VAP.

Quasi-Optical Terahertz Microfluidic Devices for Chemical Sensing and Imaging

We first review the development of a frequency domain quasi-optical terahertz (THz) chemical sensing and imaging platform consisting of a quartz-based microfluidic subsystem in our previous work. We then report the application of this platform to sensing and characterizing of several selected liquid chemical samples from 570⁻630 GHz. THz sensing of chemical mixtures including isopropylalcohol-water (IPA-H₂O) mixtures and acetonitrile-water (ACN-H₂O) mixtures have been successfully demonstrated and the results have shown completely different hydrogen bond dynamics detected in different mixture systems. In addition, the developed platform has been applied to study molecule diffusion at the interface between adjacent liquids in the multi-stream laminar flow inside the microfluidic subsystem. The reported THz microfluidic platform promises real-time and label-free chemical/biological sensing and imaging with extremely broad bandwidth, high spectral resolution, and high spatial resolution.

Current Evidence for the Use of Laminar Flow in Reducing Infection Rates in Total Joint Arthroplasty

Since the introduction of laminar air flow in orthopaedic theatres by Sir John Charnley, it has widely become accepted as the standard during orthopaedic procedures such as joint arthroplasty. We present a review of available current literature for the use of laminar flow operating theatre ventilation during total joint arthroplasty and examines the effectiveness of laminar flow ventilated operating theatres in preventing post-operative wound infection. Results of our findings suggest that while bacterial and air particulate is reduced by laminar air flow systems, there is no conclusive effect on the reduction of post-operative wound infections following total joint arthroplasty. We conclude that a combination of strict aseptic technique, prophylactic antibiotics and good anaesthetic control during surgery remains crucial to reduce post-operative surgical infections.

Investigation of Laminar Convective Heat Transfer for Al₂O₃-Water Nanofluids Flowing through a Square Cross-Section Duct with a Constant Heat Flux

The objective of this study is to numerically investigate the convective heat transfer of water-based Al₂O₃ nanofluids flowing through a square cross-section duct with a constant heat flux under laminar flow conditions. The effects of nanoparticle concentration and Peclet number on the heat transfer characteristics of Al₂O₃-water nanofluids are investigated. The nanoparticle diameter is 25 nm and six particle concentrations (0.2, 0.5, 1, 1.5, 2, and 2.5 vol.%) are considered. The numerical results show that the heat transfer coefficients and Nusselt numbers of Al₂O₃-water nanofluids increase with increases in the Peclet number as well as particle volume concentration. The heat transfer coefficient of nanofluids is increased by 25.5% at a particle volume concentration of 2.5% and a Peclet number of 7500 as compared with that of the base fluid (pure water). It is noteworthy that at the same particle volume concentration of 2.5%, the enhancement of the convective heat transfer coefficient of Al₂O₃-water nanofluid (25.5%) is much higher than that of the effective thermal conductivity (9.98%). Thus, the enhancement of the convective heat transfer cannot be solely attributed to the enhancement of the effective thermal conductivity. Additionally, the numerical results coincide well with the published experimental data.

Disturbed shear stress reduces Klf2 expression in arterial-venous fistulae in vivo

Laminar shear stress (SS) induces an antiproliferative and anti-inflammatory endothelial phenotype and increases Klf2 expression. We altered the diameter of an arteriovenous fistula (AVF) in the mouse model to determine whether increased fistula diameter produces disturbed SS in vivo and if acutely increased disturbed SS results in decreased Klf2 expression. The mouse aortocaval fistula model was performed with 22, 25, or 28 gauge needles to puncture the aorta and the inferior vena cava. Duplex ultrasound was used to examine the AVF and its arterial inflow and venous outflow, and SS was calculated. Arterial samples were examined with western blot, immunohistochemistry, and immunofluorescence analysis for proteins and qPCR for RNA. Mice with larger diameter fistulae had diminished survival but increased AVF patency. Increased SS magnitudes and range of frequencies were directly proportional to the needle diameter in the arterial limb proximal to the fistula but not in the venous limb distal to the fistula, with 22-gauge needles producing the most disturbed SS in vivo. Klf2 mRNA and protein expression was diminished in the artery proximal to the fistula in proportion to increasing SS. Increased fistula diameter produces increased SS magnitude and frequency, consistent with disturbed SS in vivo. Disturbed SS is associated with decreased mRNA and protein expression of Klf2. Disturbed SS and reduced Klf2 expression near the fistula are potential therapeutic targets to improve AVF maturation.

Microbial adhesion capacity. Influence of shear and temperature stress

Environmental parameters dictate the conditions for both biofilm formation and deconstruction. The aim of this study is to analyse the impact of hydrodynamic and thermodynamic effects on bacterial detachment. Escherichia coli grown on two stainless steel metal surfaces with different roughness (brushed with roughness of 0.05 μm and electropolished with roughness of 0.29 μm) are exposed to laminar and turbulent (shower) flows of phosphate buffered saline media at temperatures of 8, 20 and 37 °C. Results show that the turbulent flow removes significantly more bacterial cells than laminar flow (p <0.05) on both materials. This indicates that the shear force determines the rate of detached bacteria. It is also observed that detachment of cells is more efficient on brushed than on electropolished contact surfaces because on the latter surface, fewer cells were attached before exposure. Moreover, we demonstrate that the temperature of the washing agent has an impact on bacterial detachment. At the same flow conditions, the exposure to higher temperature results in greater detachment rate.

Separation of fine particles at different frequencies and HRTs using acoustic standing waves

The objective of this study was to evaluate the separation of fine particles using several frequencies and hydraulic retention times (HRTs) in an acoustic standing wave reactor without any separate cooling devices. The acoustic standing wave reactor consisted of sufficient space (over 100 mm) between the transducer and reflector, resulting in a slight increase in temperature. However, the increase in temperature did not affect the formation of standing waves and particle aggregations in our experiments. The results indicated that the turbidity removal efficiencies of fine kaolin particles, when using frequencies of 580 kHz, 1, and 2 MHz, increased with longer standing wave operation time. Especially, the turbidity removal efficiencies for 1 and 2 MHz were higher than that for 580 kHz because the wavelength (λ) of the 580 kHz wave was longer than that of the 1 and 2 MHz waves. Furthermore, the turbidity removal efficiency of kaolin in a continuous reactor improved with increasing hydraulic retention times (HRTs), and the reactor was more effective with 1 and 2 MHz used in parallel instead of 1 and 2 MHz used individually under the same HRT conditions with the entrance length (EL) having no adverse effect.

Characterization of extracellular signal-regulated kinase 5 levels in human umbilical vein endothelial cells exposed to disturbed and uniform flow

Extracellular signal-regulated kinase 5 (ERK5) has been reported to regulate endothelial cell integrity and protect from vascular dysfunction under continuous laminar flow. However, the effect of flow on ERK5 levels has not been determined. Confluent human umbilical vein endothelial cells (HUVECs) were seeded on fibronectin coated glass slides and serum starved for 2 hours with 1% fetal bovine serum (FBS). HUVECs were then exposed to to and fro flow (TFF), pulsatile forward flow (PFF), or continuous laminar flow (CLF) in a parallel plate flow chamber for up to 2 hours. At the end of experiment, cell lysates were prepared and immunoblotted with antibodies to total ERK5. Both CLF and TFF exhibited a decrease in ERK5 after levels after 2-hour exposure. However, the level of ERK5 for PFF remained the same. Disturbed, but not uniform pulsatile, flow decreases ERK5 levels in HUVECs.

Triple-deck analysis of transonic high Reynolds number flow through slender channels

In this work, laminar transonic weakly three-dimensional flows at high Reynolds numbers in slender channels, as found in microsupersonic nozzles and turbomachines of micro-electro-mechanical systems, are considered. The channel height is taken so small that the viscous wall layers forming at the channel walls start to interact strongly rather than weakly with the inviscid core flow and, therefore, the classical boundary layer approach fails. The resulting viscous-inviscid interaction problem is formulated using matched asymptotic expansions and found to be governed by a triple-deck structure. As a consequence, the properties of the predominantly inviscid core region and the viscous wall layers have to be calculated simultaneously in the interaction region. Weakly three-dimensional effects caused by surface roughness, upstream propagating flow perturbations, boundary layer separation as well as bifurcating solutions are discussed. Representative results for subsonic as well as supersonic conditions are presented, and the importance of these flow phenomena in technical applications as, for example, a means to reduce shock losses through the use of deformed geometry is addressed.

Thioredoxin-interacting protein is a biomechanical regulator of Src activity: key role in endothelial cell stress fiber formation

RATIONALE

Fluid shear stress differentially regulates endothelial cell stress fiber formation with decreased stress fibers in areas of disturbed flow compared with steady flow areas. Importantly, stress fibers are critical for several endothelial cell functions including cell shape, mechano-signal transduction, and endothelial cell-cell junction integrity. A key mediator of steady flow-induced stress fiber formation is Src that regulates downstream signaling mediators such as phosphorylation of cortactin, activity of focal adhesion kinase, and small GTPases.

OBJECTIVE

Previously, we showed that thioredoxin-interacting protein (TXNIP, also VDUP1 [vitamin D upregulated protein 1] and TBP-2 [thioredoxin binding protein 2]) was regulated by fluid shear stress; TXNIP expression was increased in disturbed flow compared with steady flow areas. Although TXNIP was originally characterized for its role in redox and metabolic cellular functions, recent reports show important scaffold functions related to its α-arrestin structure. Based on these findings, we hypothesized that TXNIP acts as a biomechanical sensor that regulates Src kinase activity and stress fiber formation.

METHODS AND RESULTS

Using en face immunohistochemistry of the aorta and cultured endothelial cells, we show inverse relationship between TXNIP expression and Src activity. Specifically, steady flow increased Src activity and stress fiber formation, whereas it decreased TXNIP expression. In contrast, disturbed flow had opposite effects. We studied the role of TXNIP in regulating Src homology phosphatase-2 plasma membrane localization and vascular endothelial cadherin binding because Src homology phosphatase-2 indirectly regulates dephosphorylation of Src tyrosine 527 that inhibits Src activity. Using immunohistochemistry and immunoprecipitation, we found that TXNIP prevented Src homology phosphatase-2-vascular endothelial cadherin interaction.

CONCLUSIONS

In summary, these data characterize a fluid shear stress-mediated mechanism for stress fiber formation that involves a TXNIP-dependent vascular endothelial cadherin-Src homology phosphatase-2-Src pathway.

Optical coherence tomography reveals a non-spasm pseudo-coronary artery stenosis: a case report and review of literature

We described a case of angiographic stenosis that was highly suitable for stenting and it remained even after repeated intracoronary administration of nitroglycerin. However, optical coherence tomography showed the stenosis disappeared and the artery wall was smooth. It was therefore speculated that this was a just non-spasm pseudo-coronary artery stenosis. We hope that sharing this experience can aid cardiologists to avoid unnecessary implantation of stents.

A laminar flow unit for the care of critically ill newborn infants

INTRODUCTION

Medical and nursing care of newborns is predicated on the delicate control and balance of several vital parameters. Closed incubators and open radiant warmers are the most widely used devices for the care of neonates in intensive care; however, several well-known limitations of these devises have not been resolved. The use of laminar flow is widely used in many fields of medicine, and may have applications in neonatal care.

OBJECTIVE

To describe the neonatal laminar flow unit, a new equipment we designed for care of ill newborns.

METHODS

The idea, design, and development of this device was completed in Sao Paulo, Brazil. The unit is an open mobile bed designed with the objective of maintaining the advantages of the incubator and radiant warmer, while overcoming some of their inherent shortcomings; these shortcomings include noise, magnetic fields and acrylic barriers in incubators, and lack of isolation and water loss through skin in radiant warmers. The unit has a pump that aspirates environmental air which is warmed by electrical resistance and decontaminated with High Efficiency Particulate Air Filter (HEPA) filters (laminar flow). The flow is directed by an air flow directioner. The unit has an embedded humidifier to increase humidity in the infant's microenvironment and a servo control mechanism for regulation of skin temperature.

RESULTS

The laminar flow unit is open and facilitates access of care providers and family, which is not the case in incubators. It provides warming by convection at an air velocity of 0.45 m/s, much faster than an incubator (0.1 m/s). The system provides isolation 1000 class (less than 1,000 particles higher than 0.3 micron per cubic feet at all times). This is much more protection than an incubator provides and more than radiant warmers, which have no isolation whatsoever. Additionally, it provides humidification of the newborn's microenvironment (about 60% relative humidity), which is impossible with a radiant warmer, which produces high water body loss. It has no mechanical barriers like acrylic walls, its magnetic field is lower than an incubator (0.25 μt versus 1.2 μt), and the noise is minimal compared to incubators. The unit is also able to provide controlled total body hypothermia, which is not possible with either of the other two units.

CONCLUSION

The laminar flow unit for neonatal care is a novel device which we recently developed. The introduction of laminar flow technology represents a real innovation in the neonatal field. We have described the various components of the unit and the potential advantages for management of ill neonates. This will hopefully lead to improved clinical outcomes and more effective neonatal management and safety.

Microfluidic platforms for single-cell protein analysis

Elucidation of the heterogeneity of cells is a challenging task due to the lack of efficient analytical tools to make measurements with single-cell resolution. Microfluidics has emerged as a powerful platform for single-cell analysis with the ability to manipulate small volume and integrate multiple sample preparation steps into one device. In this review, we discuss the differentiating advantages of microfluidic platforms that have been demonstrated for single-cell protein analysis.

Isolation of motile spermatozoa with a microfluidic chip having a surface-modified microchannel

Conventional methods to prepare sperm have been amenable to the investigation of outcomes such as rates of recovery and conventional semen parameters. The standard preparation of sperm for assisted reproduction is criticized for its centrifugation steps, which might either recover motile sperm in variable proportions or increase the probability of damage to sperm DNA. An microfluidic system was designed to separate motile sperm according to a design whereby nonmotile spermatozoa and debris flow along their initial streamlines and exit through one outlet-up, whereas motile spermatozoa have an opportunity to swim into a parallel stream and to exit through a separate outlet-down. This chip was fabricated by microelectromechanical systems technology with polydimethylsiloxane molding. The hydrophilic surface, coated with poly (ethanediol) methyl ether methacrylate, exhibits enduring stability maintained for the microchannel. Microscopic examination and fluorescent images showed that the motility of sperm varied with the laminar streams. To confirm the sorting, we identified and quantified the proportions of live and dead sperm before and after sorting with flow cytometric analysis. The results on the viability of a sample demonstrated the increased quality of sperm after sorting and collection in the outlet reservoir. The counted ratio of live sperm revealed the quantity and efficiency of the sorted sperm.

A differential pressure laminar flow reactor supports osteogenic differentiation and extracellular matrix formation from adipose mesenchymal stem cells in a macroporous ceramic scaffold

We present a laminar flow reactor for bone tissue engineering that was developed based on a computational fluid dynamics model. The bioreactor design permits a laminar flow field through its specific internal shape. An integrated bypass system that prevents pressure build-up through bypass openings for pressure release allows for a constant pressure environment during the changing of permeability values that are caused by cellular growth within a porous scaffold. A macroporous ceramic scaffold, composed of zirconium dioxide, was used as a test biomaterial that studies adipose stem cell behavior within a controlled three-dimensional (3D) flow and pressure environment. The topographic structure of the material provided a basis for stem cell proliferation and differentiation toward the osteogenic lineage. Dynamic culture conditions in the bioreactor supported cell viability during long-term culture and induced cell cluster formation and extra-cellular matrix deposition within the porous scaffold, though no complete closure of the pores with new-formed tissue was observed. We postulate that our system is suitable for studying fluid shear stress effects on stem cell proliferation and differentiation toward bone formation in tissue-engineered 3D constructs.