Shear Flow Direction Research Articles

Rapid biofabrication of cell-free, anisotropic collagen tissues using a novel horizontal shear flow technique

Ultrastructure and organisation of collagen fibres is essential to tissue function, due to the loadbearing properties of collagen. Current techniques used to create aligned collagen tissue equivalents use the contractile ability of cells to remodel and align collagen fibres or utilise highly specialised pieces of equipment. The aim of this study is to develop a novel and rapid method to produce acellular aligned collagen sheets by combining horizontal shear flow (HSFlow) and the established RAFT method to remove excess fluid from a hydrogel.Force applied to the gel during the HSFlow process was measured to allow replication of the method. Quantification of fibres and cellular alignment revealed a significant difference between HSFlow and control samples, where both cells and collagen fibres showed alignment in the direction of shear flow, compared to the randomly aligned RAFT controls. Mechanical properties were also measured and revealed that HSFlow does not appear to improve the strength of the constructs despite the improved alignment, therefore further optimisation is needed to strengthen the constructs.In conclusion, we developed a novel and rapid technique to generate flat sheets of aligned collagen without relying on the contractile ability of cells to rearrange collagen fibres. This rapid method has potential to be used in the fabrication of a scaffold to mimic anisotropic tissues for regenerative medicine.

Inhibition of Mac-1 allows human macrophages to migrate against the direction of shear flow on ICAM-1.

All immune cells must transit from the blood to distal sites such as the lymph nodes, bone marrow, or sites of infection. Blood borne monocytes traffic to the site of inflammation by adhering to the endothelial surface and migrating along endothelial intracellular adhesion molecule 1 (ICAM-1) by their ligand's macrophage 1 antigen (Mac-1) and lymphocyte functional antigen 1 (LFA-1) to transmigrate through the endothelium. Poor patient prognoses in chronic inflammation and tumors have been attributed to the hyper recruitment of certain types of macrophages. Therefore, targeting the binding of ICAM-1 to its respective ligands provides a novel approach to targeting the recruitment of macrophages. To that end, we determined whether the loss of Mac-1 expression could induce this upstream migration behavior by using blocking antibodies against Mac-1 to examine the effects of hydrodynamic flow on the migration of the human macrophage cell line U-937 on ICAM-1 surfaces. Blocking Mac-1 on U-937 cells led to upstream migration against the direction of shear flow on ICAM-1 surfaces. In sum, the ability of macrophages to migrate upstream when Mac-1 is blocked represents a new avenue to precisely control the differentiation, migration, and trafficking of macrophages.

Learning to swim efficiently in a nonuniform flow field.

Microswimmers can acquire information on the surrounding fluid by sensing mechanical queues. They can then navigate in response to these signals. We analyze this navigation by combining deep reinforcement learning with direct numerical simulations to resolve the hydrodynamics. We study how local and nonlocal information can be used to train a swimmer to achieve particular swimming tasks in a nonuniform flow field, in particular, a zigzag shear flow. The swimming tasks are (1) learning how to swim in the vorticity direction, (2) learning how to swim in the shear-gradient direction, and (3) learning how to swim in the shear-flow direction. We find that access to laboratory frame information on the swimmer's instantaneous orientation is all that is required in order to reach the optimal policy for tasks (1) and (2). However, information on both the translational and rotational velocities seems to be required to accomplish task (3). Inspired by biological microorganisms, we also consider the case where the swimmers sense local information, i.e., surface hydrodynamic forces, together with a signal direction. This might correspond to gravity or, for microorganisms with light sensors, a light source. In this case, we show that the swimmer can reach a comparable level of performance to that of a swimmer with access to laboratory frame variables. We also analyze the role of different swimming modes, i.e., pusher, puller, and neutral.

Structural Heterogeneity Dependence of the Fracture Feature Distribution in the Tensile Elongation of Microinjection Molded Polyethylene

The microscopic structure and tensile statistical fracture behavior of microinjection molded polyethylene samples with and without a weldline were investigated as a function of mold temperature using small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and stress–strain measurements. Probability density functions were adopted to describe the statistical nature of bulk mechanical parameters. The distributions of the elongation at break and fracture toughness follow a Gaussian function for the samples molded at 27 and 50 °C, whereas the fracture feature distributions deviate evidently from Gaussian statistics in the case of the samples molded at 75 °C. This discrepancy is due to the different extent of structural heterogeneity along the shear flow direction as evidenced by the distributions of crystallinity and degree of molecular orientation. Being composed of a more uniform structural distribution on both the lamellar and molecular length scales across the length, a fraction of the samples molded at 75 °C can surpass the barrier of localized homogeneous deformation as observed in the ones produced at low mold temperatures upon tensile stretching and thus are globally elongated to a large strain before ultimate failure, resulting finally in a broad non-Gaussian distribution of the fracture parameters. The fracture toughness–yield stress relationships revealed that the degree of orientation of the polymeric chains is of more importance than the crystallinity with regard to the fracture toughness.

Effect of l-cysteine and l-ascorbic acid addition on properties of meat analogues

Currently, studies are underway to use pea protein isolate (PPI) for the production of meat analogues because it is considered as a more sustainable alternative to soy. The potential of PPI has been demonstrated in extrusion and PPI in combination with wheat gluten has been studied in the shear cell. To enlarge the possibilities to make meat analogues with a broader range of properties, the effects of l -cysteine (CYS) and l -ascorbic acid (AA) on PPI and wheat gluten (WG) blends were examined at different concentrations (0, 100, 500, 1000 and 2000 ppm). The results showed that both CYS and AA altered the properties of the products formed by the high-temperature shear cell (HTSC). Both additives altered the fibrousness and the mechanical properties of the products obtained after processing. Especially CYS revealed an increase in tensile stress, tensile strain and Young's modulus as its concentration increased. However, products containing CYS depicted a relatively stable anisotropic index of 1, which corresponded to a densely packed matrix that was observed by microstructural analysis. A small elevated anisotropic index (>1) of products containing AA at concentrations of 500–2000 ppm could be attributed to the formation of pores parallel to the shear flow direction in these samples visualized by a confocal laser scanning microscope (CLSM) and the scanning electron microscope (SEM). In the products containing 2000 ppm of AA and 2000 ppm CYS, small and large fibers were formed, respectively. Therefore, this research pointed out the potential application of CYS and AA to alter and control the textural attributes of products. This application could aid in improving the consumer acceptance of meat analogues and, thus, contribute to being able to feed the increasing population of the world. • l -cysteine and l -ascorbic acid were examined for the production of meat analogue. • They altered properties of products formed by high-temperature shear cell. • l -cysteine increased tensile stress, tensile strain and Young's modulus of products. • l -ascorbic acid increased the browning index, fiber formation and anisotropy index.

Direct observation of deformation of individual red blood cells in oscillatory fluid flow produced using a generator of precise sinusoidal shear flow

We report the development of a precision sinusoidal shear flow generator that creates an oscillatory shear flow in the narrow gap between two parallel glass plates moving in opposite directions, thereby allowing direct observation of the cyclical deformation and recovery of a single red blood cell (RBC). The system is used to demonstrate that RBCs change their shape with cyclical elongation and shape recovery and align with the fluid streamlines in the direction of laminar Couette shear flow. From six repetitions, it can be seen that the curvature showing the time series of the elongation index (EI) of an RBC in sinusoidal shear flow in the present device was highly symmetrical and there were no significant differences at a 95% confidence interval. Moreover, the system provides details about the deformation characteristics of an RBC, which have four phases: (i) low deformation, in which the EI is minimal and the RBC mostly retains its original circular shape; (ii) shape elongation, in which the RBC loaded with shear forces begins to change its shape dynamically from circular to oval; (iii) steady deformation, in which the EI is constant and the shape of the RBC is elliptical throughout; and (iv) shape recovery, in which the EI decreases and the RBC becomes oval with trailing endpoints. Along with this information, the developed measurement system has potential application in clinical and biological analyses of RBC deformability.

Development of a Flexible MEMS Sensor for Subsonic Flow.

Detection and control of flow separation is a key to improving the efficiency of fluid machinery. In this study, we developed a flexible MEMS (microelectromechanical systems) sensor for measuring the wall shear stress and flow angle in subsonic airflow. The developed sensor is made of a flexible polyimide film and a microheater surrounded by three temperature sensor pairs. The sensor measures the wall shear stress from the heater output and the flow angle from the temperature gradient around the heater. The geometry and design of the heater and temperature sensors were determined based on numerical simulations. To evaluate the validity of the sensor, we conducted an experiment to measure the wall shear stress and the flow angle in a wind tunnel in different velocities ranging from 30 m/s to 170 m/s, equivalent to Mach numbers from 0.1 to 0.5. The heater output was proportional to one-third power of the wall shear stress. Additionally, the bridge output correlating the temperature difference between two opposing temperature sensors showed sinusoidal variation depending on the flow angle. Consequently, we have clarified that the developed sensor can measure both the wall shear stress and flow direction in subsonic flow.

Shear rheology of a dilute emulsion of ferrofluid droplets dispersed in a nonmagnetizable carrier fluid under the influence of a uniform magnetic field

The effect of a spatially uniform magnetic field on the shear rheology of a dilute emulsion of monodispersed ferrofluid droplets, immersed in a nonmagnetizable immiscible fluid, is investigated using direct numerical simulations. The direction of the applied magnetic field is normal to the shear flow direction. The droplets' extra-stress tensor arising from the presence of interfacial forces of magnetic nature is modeled on the basis of the seminal work of G. K. Batchelor [J. Fluid Mech. 41, 545–570 (1970)] under the assumptions of a linearly magnetizable ferrofluid phase and negligible inertia. The results show that even relatively small magnetic fields can have significant consequences on the rheological properties of the emulsion due to the magnetic forces that contribute to deform and orient the droplets toward the direction of the applied magnetic vector. In particular, we have observed an increase in the effective (bulk) viscosity and a reversal of the sign of the two normal stress differences with respect to the case without magnetic field for those conditions where the magnetic force prevails over the shearing force. Comparisons between the results of our model with a direct integration of the viscous stress have provided an indication of its reliability to predict the effective viscosity of the suspension. Moreover, this latter quantity has been found to behave as a monotonic increasing function of the applied magnetic field for constant shearing flows (“magneto-thickening” behavior), which allowed us to infer a simple constitutive equation describing the emulsion viscosity.

Direct Observation of the Relationship between Thixotropic Behavior and Shear-Induced Orientation of Clay Particles in Synesthetic Hectorite Suspensions.

A thixotropic characteristics of aqueous gels containing smectite clay minerals were used in various industrial applications such as paint additives, which have been affected by the clay types and clay particle sizes. A model called a house-of-card arrangement of clay particles and anisotropic arrangement in aqueous gels has been proposed. We prepared different sizes of synthetic hectorite and studied them by scanning electron-assisted dielectric microscopy (SE-ADM) and simultaneous small-angle neutron scattering and rheological measurements (Rheo-SANS). The Rheo-SANS results indicated that the clay particles with the cross-sectional radius of 30 nm were clearly oriented in the direction of shear-flow (1 × 103 s-1) direction, but the anisotropic change was not observed for an aqueous gel with clays whose average radius was 19.5 nm. The present study suggested the thixotropic characteristics of aqueous gels depend on the hectorite particle size and aggregation structure under shear conditions.

Piezo1 promotes ER Ca 2+ transport to regulate the cellular responses of endothelial cells to shear stress

Mechanotransduction is an essential mechanism by which endothelial cells (ECs) sense and adapt to the environment. Piezo1, a mechanosensitive cation channel, is responsible for sensing and transducing mechanical stimuli into chemical signals in endothelial cells. However, the signaling mechanism downstream of Piezo1 remains poorly understood. Here, we identified Piezo1-mediated ER Ca2+ transport as an essential element of endothelial cell adaptation to shear stress. Using the ER targeted calcium sensor G-Cepia1er, we showed that both laminal fluid shear and pharmacological activation of Piezo1 induced Ca2+ER transport. Activation of Piezo1 led to rapid influx of Ca2+ in the ER followed by Ca2+ER release via cAMP-sensitized Inositol TrisphosphateReceptor 2 (IP3R2), a calcium channel located in the ER membrane. Inhibition of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) blocked Piezo1-induced Ca2+entry in the ER but did not affect the rate of Ca2+ER release. In contrast, depletion of soluble Adenylyl Cyclase (sAC) markedly reduced the rate of Piezo1-mediated Ca2+ER release without affecting Ca2+entry. These data indicate that the ER Ca2+ transport induced by shear stress is finely regulated by Piezo1 downstream signaling. Furthermore, depletion of Piezo1, IP3R2 and sAC blocked alignment of ECs in the direction of shear flow. Our results provide evidence on how mechanical forces are transmitted to cellular organelles such as the ER and, for the first time, establish the role of Piezo1-sAC-IP3R2 mediated ER Ca2+ transport as an essential signaling element of cell adaptation to mechanical cues.

Integrin Crosstalk Modulates Stiffness-independent Motility in CD4+ T Lymphocytes

CD4+ T lymphocytes interact with various cell types and tissue substrates in response to inflammation.Mechanotransduction in T lymphocytes is frequently studied at immunological synapses (IS) during T cell activation, after engagement with T cell receptors (TCR) and costimulatory receptors (i.e. CD3/CD28) and LFA-1 integrins. Recently, in vitro and in vivo studies suggest T cells can migrate upstream (i.e. in the opposite direction of shear flow) on surfaces expressing ICAM-1 through interaction with LFA-1 integrins. LFA-1 likely interacts as a mechanosensor, and thus we hypothesized that substrate mechanics might affect the ability of LFA-1 to support upstream migration of T cells under flow. To test the hypothesis, we measured motility of activated primary human CD4+ T lymphocytes on polyacrylamide gels with pre-determined stiffnesses, functionalized with protein A/G and ICAM-1, VCAM-1, or 1:1 mixture of ICAM-1/VCAM-1 Fc chimeras. We found that CD4+ T cells exhibit stiffness-dependent motility on ICAM-1 surfaces, with a maximum random motility appearing at an elasticity of about 60 kPa. in contrast, motility on VCAM-1 or 1:1 mixture of VCAM-1/ICAM-1 mixed surfaces was independent of elasticity. This mechanosensitivity on ICAM-1 surfaces is overcome when VLA-4 is ligated with soluble VCAM-1. Lastly, we observed that CD4+ T cells can migrate upstream under flow on hydrogels functionalized with ICAM-1, independent of substrate stiffness. In this study, we show that CD4+ T cells can sense stiffness with integrins alone under static conditions and that integrin crosstalk can activate an elasticity-independent motility. interestingly, CD4+ T lymphocytes migrated upstream under flow on ICAM-1 substrates regardless of the substrate stiffness.

Texturized mung bean protein as a sustainable food source: Effects of extrusion on its physical, textural and protein quality

Despite being inexpensive and a sustainable source of plant protein, mung bean remains underutilized due to its hard-to-cook characteristics. The aim of this study is to produce texturized mung bean protein (TMBP) with desirable physical properties, through optimization of extrusion parameters determined as follows: 49.33% feed moisture, 80.66 rpm screw speed and 144.57 °C barrel temperature. Under these conditions, all physical properties (expansion ratio, bulk density, rehydration ratio, water absorption capacity and degree of texturization) are desirably altered. Microstructure analysis reveals fibrous structure that is aligned along the shear flow direction in TMBP while SDS-PAGE shows partial protein unfoldment that is crucial for protein fibril formation during texturization. Amino acid profile shows high retention of amino acids after texturization. Current study successfully demonstrates the optimized production of TMBP from mung bean protein with strong potential as meat extender to serve as a healthier option compared to animal proteins. Industrial relevanceCurrent work is conducted on a pilot-scale basis, from initial protein extraction up to final extrusion step. This allows food industry to readily adapt the processing parameters, as detailed in current work, for customized production of texturized mung bean protein.

LFA-1 signals to promote actin polymerization and upstream migration in T cells.

T cell entry into inflamed tissue requires firm adhesion, cell spreading, and migration along and through the endothelial wall. These events require the T cell integrins LFA-1 and VLA-4 and their endothelial ligands ICAM-1 and VCAM-1, respectively. T cells migrate against the direction of shear flow on ICAM-1 and with the direction of shear flow on VCAM-1, suggesting that these two ligands trigger distinct cellular responses. However, the contribution of specific signaling events downstream of LFA-1 and VLA-4 has not been explored. Using primary mouse T cells, we found that engagement of LFA-1, but not VLA-4, induces cell shape changes associated with rapid 2D migration. Moreover, LFA-1 ligation results in activation of the phosphoinositide 3-kinase (PI3K) and ERK pathways, and phosphorylation of multiple kinases and adaptor proteins, whereas VLA-4 ligation triggers only a subset of these signaling events. Importantly, T cells lacking Crk adaptor proteins, key LFA-1 signaling intermediates, or the ubiquitin ligase cCbl (also known as CBL), failed to migrate against the direction of shear flow on ICAM-1. These studies identify novel signaling differences downstream of LFA-1 and VLA-4 that drive T cell migratory behavior.This article has an associated First Person interview with the first author of the paper.

Human Neutrophils Will Crawl Upstream on ICAM-1 If Mac-1 Is Blocked

The recruitment of neutrophils to sites of inflammatory insult is a hallmark of the innate immune response. Neutrophil recruitment is regulated by a multistep process that includes cell rolling, activation, adhesion, and transmigration through the endothelium commonly referred to as the leukocyte adhesion cascade. After selectin-mediated braking, neutrophils migrate along the activated vascular endothelium on which ligands, including intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), are expressed. Previous studies have shown that two cells that commonly home from blood vessel to tissue—T cells and hematopoietic stem and progenitor cells—use the integrin lymphocyte functional antigen-1 (LFA-1) to migrate against the direction of shear flow once adherent on ICAM-1 surfaces. Like T cells and hematopoietic stem and progenitor cells, neutrophils express LFA-1, but they also express macrophage-1 antigen (Mac-1), which binds to ICAM-1. Previous reports have shown that neutrophils will not migrate against the direction of flow on ICAM-1, but we hypothesized this was due to the influence of Mac-1. Here, we report that both the HL-60 neutrophil-like cell line and primary human neutrophils can migrate against the direction of fluid flow on ICAM-1 surfaces via LFA-1 if Mac-1 is blocked; otherwise, they migrate downstream. We demonstrate this both on ICAM-1 surfaces and on activated endothelium. In sum, both LFA-1 and Mac-1 binding ICAM-1 play a critical role in determining the direction of neutrophil migration along the endothelium, and their interaction may play an important role in controlling neutrophil trafficking during inflammation.

An experimental investigation of the melting process of an ice bead on the smooth and micro-grooved surfaces under a hot shear flow

In the present study, we experimentally investigated the melting process of an ice bead on the smooth and micro-grooved surfaces under a hot shear flow. One smooth silicon surface and three micro-grooved silicon surfaces were fabricated and tested. A parameter study of the substrate surface temperature and the air flow speed was conducted. During the experiment, an ice bead was first formed from a freezing water droplet on a cold substrate surface. Then, the ice bead was exposed to a hot shear flow and its melting process was recorded by a CCD camera and an infrared camera simultaneously. As for the micro-grooved surfaces, the direction of the hot shear flow was parallel to the micro-grooves. The results showed that the melting process of the ice bead on the smooth and micro-grooved surfaces under a hot shear flow could be divided into three categories. The air flow speed, the surface temperature, and the type of the surface had a significant influence on which category the melting process of the ice bead belonged to. Besides, the presence of the micro-grooves was found to apparently affect the wetting length, the removable time, and the temperature along the centerline of the ice bead. In general, the micro-grooved surfaces were found to be more favorable for the ice bead melting process than the smooth surface.

DEM investigation of shear flows of binary mixtures of non-spherical particles

Discrete element method (DEM) simulations of shear flows of binary mixtures of large non-spherical glued-sphere particles and small spheres are conducted in order to investigate the effect of particle shape and solid volume fraction ratio on the behavior of binary granular flows. The shear stresses first decrease and then increase with total solid volume fraction. The shear stresses increase with the increasing solid volume fraction ratio of large particles. The orientation distributions of large particles show that, in dense regions, the binary system with a higher solid fraction ratio of small spheres exhibits a more uniform alignment in the shear flow direction for large particles. By incorporating the effective particle projected area in the plane perpendicular to the flow plane, the conventional kinetic theory for binary spherical systems is found capable of predicting the stresses for binary systems of non-spherical particles. Stresses for binary systems with various solid volume fraction ratios collapse into a single line by further incorporating the root-mean-cubed diameter, but this scaling is not adequate for dense flows. Comparing the shear stresses for different large particle shapes shows that shear stresses can be affected by the particle shape and particle aspect ratio, but the differences between different particle shapes and aspect ratios are minimized by increasing the solid volume fraction ratio of small spheres.

Plasma Transport Driven by the Three‐Dimensional Kelvin‐Helmholtz Instability

AbstractIt has been well demonstrated that the nonlinear Kelvin‐Helmholtz (KH) instability plays a critical role for the solar wind interaction with the Earth's magnetosphere. Although the two‐dimensional KH instability has been fully explored during the past decades, more and more studies show the fundamental difference between the two‐ and three‐dimensional KH instability. For northward interplanetary magnetic field (IMF) conditions, the nonlinear KH wave that is localized in the vicinity of the equatorial plane can dramatically bend the magnetic field line, generating strong antiparallel magnetic field components at high latitudes in both North and South Hemispheres, which satisfy the onset condition for magnetic reconnection. This high‐latitude double reconnection process can exchange the portion of magnetosheath and magnetospheric flux tubes between those two reconnection sites. This study used a high‐resolution 3‐D magnetohydrodynamic simulation to demonstrate that nonlinear KH waves can generate a large amount of double‐reconnected flux during the northward IMF condition, which can efficiently transport the plasma with a high diffusion coefficient of 1 × 1010 m2 s−1 for typical magnetopause conditions at the Earth. The presence of the magnetic field component along the shear flow direction not only decreases the KH growth rate but also causes north‐south asymmetry, which generates more open flux and reduces the efficiency of the plasma transport process.

Effect of uniform electric field on the drop deformation in simple shear flow and emulsion shear rheology

Electrohydrodynamic deformation and orientation of a neutrally buoyant, leaky dielectric, Newtonian drop suspended in another immiscible, leaky dielectric, Newtonian medium is analyzed under the combined influence of uniform electric field and simple shear flow. Application of uniform electric field, perpendicular to the direction of shear flow, not only deforms the drop but also modifies the rheological behavior of a dilute emulsion. In the creeping flow limit, an analytical solution for the deformed drop shape is obtained when the drop shape remains nearly spherical and the surface charge convection is weak. The effective shear rheology is obtained for a dilute emulsion of non-interacting drops by calculating the one-particle contribution to the emulsion stress. The results show that the combined influence of uniform electric field and shear flow is not a simple linear superposition of the independent contributions from electric field and shear flow. Application of uniform electric field always leads to larger drop deformation with drop inclination more towards the direction of velocity gradient for the particular case of perfectly dielectric drops. Presence of surface charge convection for a leaky dielectric drop can increase or decrease the drop deformation with the drop inclination more towards either the direction of shear flow or velocity gradient. The effective shear viscosity and normal stress differences are found to be independent of shear rate. These quantities are significantly affected by the surface charge convection and shape deformation. Shape deformation always increases the effective viscosity of a dilute emulsion composed of perfectly dielectric drops. Interestingly, for a dilute emulsion composed of leaky dielectric drops, results show that the combined influence of charge convection and shape deformation can augment or decrease the effective shear viscosity.

High temperature gradient micro-sensor for wall shear stress and flow direction measurements

We present an efficient and high-sensitive thermal micro-sensor for near wall flow parameters measurements. By combining substrate-free wire structure and mechanical support using silicon oxide micro-bridges, the sensor achieves a high temperature gradient, with wires reaching 1 mm long for only 3 μm wide over a 20 μm deep cavity. Elaborated to reach a compromise solution between conventional hot-films and hot-wire sensors, the sensor presents a high sensitivity to the wall shear stress and to the flow direction. The sensor can be mounted flush to the wall for research studies such as turbulence and near wall shear flow analysis, and for technical applications, such as flow control and separation detection. The fabrication process is CMOS-compatible and allows on-chip integration. The present letter describes the sensor elaboration, design, and micro-fabrication, then the electrical and thermal characterizations, and finally the calibration experiments in a turbulent boundary layer wind tunnel.

Wall Shear Stress and Flow Direction Thermal MEMS Sensor for Separation Detection and Flow Control Applications

We report a study on a wall shear stress and flow direction hot-wire based sensor operating in anemometric mode. The sensor is designed to achieve fast response time and high sensitivity. The sensor structure consists in free hot wires over insulator bridges and exhibits sensitivity to wall shear stress variations and to flow direction. The sensor can be wall-mounted for applications such as flow control or turbulence analysis. Finite elements simulations have been made to demonstrate a fast thermal response time to fluid velocity of about 300 μs in constant current operating mode and a sensitivity to wall shear-stress fluctuations. Electrical characterizations and wind tunnel experiments were performed to analyze the sensor response to respectively heat power and flow velocity.