Confocal micro-PIV Research Articles

The Complexity of Porous Media Flow Characterized in a Microfluidic Model Based on Confocal Laser Scanning Microscopy and Micro-PIV

In this study, the complexity of a steady-state flow through porous media is revealed using confocal laser scanning microscopy (CLSM). Micro-particle image velocimetry (micro-PIV) is applied to construct movies of colloidal particles. The calculated velocity vector fields from images are further utilized to obtain laminar flow streamlines. Fluid flow through a single straight channel is used to confirm that quantitative CLSM measurements can be conducted. Next, the coupling between the flow in a channel and the movement within an intersecting dead-end region is studied. Quantitative CLSM measurements confirm the numerically determined coupling parameter from earlier work of the authors. The fluid flow complexity is demonstrated using a porous medium consisting of a regular grid of pores in contact with a flowing fluid channel. The porous media structure was further used as the simulation domain for numerical modeling. Both the simulation, based on solving Stokes equations, and the experimental data show presence of non-trivial streamline trajectories across the pore structures. In view of the results, we argue that the hydrodynamic mixing is a combination of non-trivial streamline routing and Brownian motion by pore-scale diffusion. The results provide insight into challenges in upscaling hydrodynamic dispersion from pore scale to representative elementary volume (REV) scale. Furthermore, the successful quantitative validation of CLSM-based data from a microfluidic model fed by an electrical syringe pump provided a valuable benchmark for qualitative validation of computer simulation results.Graphic

Vapor mediated interaction of two condensing droplets

The present work investigates the internal flow structure of two condensing droplets of aqueous solution during interaction. Velocity of fluid inside the droplets was investigated by confocal micro-PIV technique. Simulation study has also been carried out to supplement the understanding of internal hydrodynamics inside droplets. Condensation on the droplets was carried out inside a closed chamber by generating a difference in vapor pressure between the droplet interface and a reservoir fluid surrounding the droplet in the room temperature without any cooling. Condensation on the droplet leads to spatial variation of solute concentration inside the droplet causing buoyancy driven Rayleigh convection. Fluid flow pattern inside a single condensing droplet is symmetric in nature whereas the fluid flow pattern for two condensing droplets is asymmetric in nature. The neighboring droplet influences the internal convection through vapor mediated interaction between the two condensing droplets. The condensing droplet senses the neighboring droplet from a distance without any physical contact. The asymmetric nature of the flow pattern is attributed to the modification in the distribution of condensation flux of the droplet in the presence of the neighboring droplet. The flow pattern observed for interacting droplets during condensation is opposite to that of evaporating droplets. The effect of the neighboring droplet on the internal convection of the condensing droplet reduces with increase in separation distance between the droplets.

Phase-locked confocal micro-PIV measurement for 3D flow structure of transient droplet formation mechanism in T-shaped microjunction

This paper aims to develop a phase-locked multicolor confocal micro-particle image velocimetry (PIV) technique to investigate the flow mechanism of microdroplet formation at a micro T-shaped micro junction. The object to be measured is a three-dimensional (3D) periodic multiphase flow with random disturbances, and this method is a solution for the 3D flow measurement of this complicated phenomenon. The phase-locking technique is needed to reconstruct the 3D flow field from the two-dimensional (2D) confocal micro-PIV measurement data. We successfully obtained each temporal phase of the periodic phenomenon noninvasively by detecting the passage of a droplet from the transmitted light of an optical proximity sensor. Then, the phase-locking technique also enabled us to select the same conditions of formation frequency, size, and translational velocity of droplets to minimize instability in the droplet formation phenomenon. The multicolor system can measure the dynamic behavior of each phase of a multiphase flow separately and simultaneously. As a result, the 3D flow structure of droplet formation was successfully reconstructed and investigated with high spatial and temporal resolution.

Velocity profile of thin film flows measured using a confocal microscopy particle image velocimetry system with simultaneous multi depth position

In this paper, we report a technique for simultaneously visualizing flows near walls at nano-depth positions. To achieve such a high interval of depth gradient, we developed a tilted observation technique in a particle image velocimetry (PIV) system based on confocal microscopy. The focal plane along the bottom of the flow channel was tilted by tilting the micro-channel, enabling depth scanning in the microscopic field of view. Our system is suitable for measuring 3D two-component flow fields. The depth interval was approximately 220 nm over a depth range of 10 μm, depending on the tilt angle of the micro-channel. Applying the proposed system, we visualized the near-wall flow in a drainage film flow under laminar conditions to the depth of approximately 30 μm via vertical scanning from the bottom to the free surface. The velocity gradient was proportional to the distance from the wall, consistent with theoretical predictions. From the measured near-wall velocity gradient, we calculated the wall shear stress. The measurement accuracy was approximately 1.3 times higher in our proposed method than in the conventional confocal micro-PIV method.

1205 共焦点マイクロPIVと超解像度顕微鏡の組み合わせによる血管内皮細胞グリコカリックス層近傍の速度分布計測

1205 共焦点マイクロPIVと超解像度顕微鏡の組み合わせによる血管内皮細胞グリコカリックス層近傍の速度分布計測

W053001 血管内皮細胞近傍の流動の高解像度計測法(【W05300】血視研(血流の視える化研究),流体工学部門,バイオエンジニアリング部門,マイクロ・ナノ工学部門企画,ワークショップ)

To investigate an influence of a glycocalyx surface layer covering over endothelial cells (ECs) on the flow field or flow through the layer, a high spatial resolution measurement technique was improved for three-dimensional velocity distributions close to a glycocalyx layer by utilizing a confocal micro-PIV (Particle Image Velocimetry) technique. The developed technique achieved to measure three-dimensional velocity distributions in a 177×177×3μm^3 region with in-plane resolution of 7 μm and with depth resolution of 0.5 μm. Three-dimensional velocity distribution close to the layer of living ECs cultured in microchannel was measured. The results suggested that the developed technique was useful for investigation of velocity field close to the layer.

Continuous and simultaneous measurement of the tank-treading motion of red blood cells and the surrounding flow using translational confocal micro-particle image velocimetry (micro-PIV) with sub-micron resolution

In this study, a translational confocal micro-particle image velocimetry (PIV) system is introduced to measure the microscopic interaction between red blood cells (RBCs) and the surrounding flow. Since the macroscopic behavior of RBCs, such as the tank-treading motion, is closely related to the axial migration and other flow characteristics in arterioles, the measurement method must answer the conflicting demands of sub-micron resolution, continuous measurement and applicability for high-speed flow. In order to avoid loss of the measurement target, i.e. RBCs, from the narrow field of view during high-magnification measurement, the translation stage with the flow device moves in the direction opposite the direction of flow. The proposed system achieves the measurement of higher absolute velocities compared with a conventional confocal micro-PIV system without the drawbacks derived from stage vibration. In addition, we have applied a multicolor separation unit, which can measure different phases simultaneously using different fluorescent particles, in order to clarify the interaction between RBCs and the surrounding flow. Based on our measurements, the tank-treading motion of RBCs depends on the shear stress gradient of the surrounding flow. Although, the relationship between the tank-treading frequency and the shear rate of the surrounding flow is of the same order as in the previous uniform shear rate experiments, our results reveal the remarkable behavior of the non-uniform membrane velocities and lateral velocity component of flow around the RBCs.

8F22 共焦点マイクロPIV法によるマイクロ流路内の血管内皮細胞にかかるせん断応力分布と形状の時間的変化(OS16 血球運動と微小環境のバイオニクス2)

8F22 共焦点マイクロPIV法によるマイクロ流路内の血管内皮細胞にかかるせん断応力分布と形状の時間的変化(OS16 血球運動と微小環境のバイオニクス2)

Simultaneous measurement of internal and surrounding flows of a moving droplet using multicolour confocal micro-particle image velocimetry (micro-PIV)

This paper presents a micro-multiphase flow measurement technique, ‘multicolour confocal micro-particle image velocimetry (PIV), and its application to the internal and surrounding flow measurement of a droplet moving through a microchannel. The present system measures the dynamic interaction between flows in two different phases, such as solid–liquid or liquid–liquid, simultaneously and separately. Unlike conventional confocal micro-PIV, this system features a wavelength separation optical device. The optical components (e.g., filters and dichroic mirror) are designed to separate fluorescent lights of tracer particles and to eliminate unnecessary scattered light depending on the characteristic wavelengths. The system can record a sequence of images at up to 2000 frames per second. It also has an in-plane spatial resolution of 0.284 µm/pixel in a field of 227.2 µm × 170.4 µm and a confocal depth of 3.43 µm using ∅1.0 µm particles and a 40× objective lens. This paper examines the performance of the present system, such as its ability to separate wavelengths. Furthermore, this system is applied to liquid–liquid two-phase flow, which consists of a water droplet and surrounding oil flow, in a microchannel. We succeeded in measuring each phase movement separately and simultaneously. As a result of the estimation of the out-of-plane velocity component, a three-dimensional flow structure is obtained and the interaction between each phase is investigated.

187 共焦点micro-PIVによる円管内の大腸菌懸濁液の流動計測(バイオエンジニアリングII,一般講演)

187 共焦点micro-PIVによる円管内の大腸菌懸濁液の流動計測(バイオエンジニアリングII,一般講演)

Asymmetry of blood flow and cancer cell adhesion in a microchannel with symmetric bifurcation and confluence

Bifurcations and confluences are very common geometries in biomedical microdevices. Blood flow at microchannel bifurcations has different characteristics from that at confluences because of the multiphase properties of blood. Using a confocal micro-PIV system, we investigated the behaviour of red blood cells (RBCs) and cancer cells in microchannels with geometrically symmetric bifurcations and confluences. The behaviour of RBCs and cancer cells was strongly asymmetric at bifurcations and confluences whilst the trajectories of tracer particles in pure water were almost symmetric. The cell-free layer disappeared on the inner wall of the bifurcation but increased in size on the inner wall of the confluence. Cancer cells frequently adhered to the inner wall of the bifurcation but rarely to other locations. Because the wall surface coating and the wall shear stress were almost symmetric for the bifurcation and the confluence, the result indicates that not only chemical mediation and wall shear stress but also microscale haemodynamics play important roles in the adhesion of cancer cells to the microchannel walls. These results provide the fundamental basis for a better understanding of blood flow and cell adhesion in biomedical microdevices.

Particle Image Velocimetry of the Blood Flow in a Micro-channel Using the Confocal Laser Scanning Microscope

We used video-rate Confocal Laser Scanning Microscopy (CLSM) to observe the motion of blood cells in a micro-channel. Video-rate CLSM allowed us to acquire images at the rate of 30 frames per second. The acquired images were used to perform Particle Image Velocimetry (PIV), thus providing the velocity profile of the blood in a micro-channel. While previous confocal microscopy-assisted PIV required exogenous micro/nano particles as the tracing particles, we employed blood cells as tracing particles for the CLSM in the reflection mode, which uses light back-scattered from the sample. The blood flow at various depths of the micro-channel was observed by adjusting the image plane of the microscope. The velocity profile at different depths of the channel was measured. The confocal micro-PIV technique used in the study was able to measure blood velocity up to a few hundreds <TEX>${\mu}m/sec$</TEX>, equivalent to the blood velocity in the capillaries of a live animal. It is expected that the technique presented can be applied for in vivo blood flow measurement in the capillaries of live animals.

Confocal micro-PIV measurement of droplet formation in a T-shaped micro-junction

This paper aims to investigate a mechanism of microdroplet formation using "multicolor confocal micro particle image velocimetry (PIV)" technique. The present system can measure dynamical behavior of multiphase flow separately and simultaneously. It also enables to identify the interactions between two immiscible fluids. We have applied this system to measure the water droplet formation at a micro T-shaped junction. We have also succeeded in dispersing fluorescent tracer particles into both phases. The interaction between the internal flow of to-be-dispersed water phase and of continuous oil phase is measured as a liquid-liquid multiphase flow. As a result of PIV measurement and interface scanning, the relationship between flow structure of each phase and interface shape is clarified. It indicates that the gap between the tip of to-be-dispersed phase and capillary wall, and interface area play an important role in the flow structure and shear stress on the interface.

10603 赤血球と周囲流体の相互作用の可視化計測に向けた共焦、点マイクロPIVシステムの開発(流体測定技術の新展開(1),OS.12 流体測定技術の新展開)

A new confocal micro-PIV system is developed using a motorized microscope stage. The system allows us to measure micro-scale flow with high spatial resolution in higher speed than that of conventional system. The system has a potential to experimentally investigate the interaction between red blood cells (RBC) and surrounding flow under biological environment. In order to investigate a performance of the system, we measured Poiseuule flow under both the present and the conventional system, and compared the results.

215 微小流路内の分岐部及び合流部における血流の共焦点マイクロPIV計測(OS1-3:循環器系のバイオメカニクス(3),OS1:循環器系のバイオメカニクス)

215 微小流路内の分岐部及び合流部における血流の共焦点マイクロPIV計測(OS1-3:循環器系のバイオメカニクス(3),OS1:循環器系のバイオメカニクス)

In vitro blood flow in a rectangular PDMS microchannel: experimental observations using a confocal micro-PIV system

Progress in microfabricated technologies has attracted the attention of researchers in several areas, including microcirculation. Microfluidic devices are expected to provide powerful tools not only to better understand the biophysical behavior of blood flow in microvessels, but also for disease diagnosis. Such microfluidic devices for biomedical applications must be compatible with state-of-the-art flow measuring techniques, such as confocal microparticle image velocimetry (PIV). This confocal system has the ability to not only quantify flow patterns inside microchannels with high spatial and temporal resolution, but can also be used to obtain velocity measurements for several optically sectioned images along the depth of the microchannel. In this study, we investigated the ability to obtain velocity measurements using physiological saline (PS) and in vitro blood in a rectangular polydimethysiloxane (PDMS) microchannel (300 microm wide, 45 microm deep) using a confocal micro-PIV system. Applying this combination, measurements of trace particles seeded in the flow were performed for both fluids at a constant flow rate (Re = 0.02). Velocity profiles were acquired by successive measurements at different depth positions to obtain three-dimensional (3-D) information on the behavior of both fluid flows. Generally, the velocity profiles were found to be markedly blunt in the central region, mainly due to the low aspect ratio (h/w = 0.15) of the rectangular microchannel. Predictions using a theoretical model for the rectangular microchannel corresponded quite well with the experimental micro-PIV results for the PS fluid. However, for the in vitro blood with 20% hematocrit, small fluctuations were found in the velocity profiles. The present study clearly shows that confocal micro-PIV can be effectively integrated with a PDMS microchannel and used to obtain blood velocity profiles along the full depth of the microchannel because of its unique 3-D optical sectioning ability. Advantages and disadvantages of PDMS microchannels over glass capillaries are also discussed.

Three-dimensional measurement and visualization of internal flow of a moving droplet using confocal micro-PIV

This paper presents a micro-flow diagnostic technique, 'high-speed confocal micro-particle image velocimetry (PIV)', and its application to the internal flow measurement of a droplet passing through a microchannel. A confocal micro-PIV system has been successfully constructed wherein a high-speed confocal scanner is combined with the conventional micro-PIV technique. The confocal micro-PIV system enables us to obtain a sequence of sharp and high-contrast cross-sectional particle images at 2000 frames s(-1). This study investigates the confocal depth, which is a significant parameter to determine the out-of-plane measurement resolution in confocal micro-PIV. Using the present confocal micro-PIV system, we can measure velocity distributions of micro-flows in a 228 microm x 171 microm region with a confocal depth of 1.88 microm. We also propose a three-dimensional velocity measurement method based on the confocal micro-PIV and the equation of continuity. This method enables us to measure three velocity components in a three-dimensional domain of micro flows. The confocal micro-PIV system is applied to the internal flow measurement of a droplet. We have measured three-dimensional distributions of three-component velocities of a droplet traveling in a 100 microm (width) x 58 microm (depth) channel. A volumetric velocity distribution inside a droplet is obtained by the confocal micro-PIV and the three-dimensional flow structure inside the droplet is investigated. The measurement results suggest that a three-dimensional and complex circulating flow is formed inside the droplet.

1121 共焦点micro-PIVによる微小流路内の血流観察(J05-1 血液循環系のバイオエンジニアリング:医療技術への展開(1),J05 血液循環系のバイオエンジニアリング:医療技術への展開)

1121 共焦点micro-PIVによる微小流路内の血流観察(J05-1 血液循環系のバイオエンジニアリング:医療技術への展開(1),J05 血液循環系のバイオエンジニアリング:医療技術への展開)

In vitro confocal micro-PIV measurements of blood flow in a square microchannel: The effect of the haematocrit on instantaneous velocity profiles

A confocal microparticle image velocimetry (micro-PIV) system was used to obtain detailed information on the velocity profiles for the flow of pure water (PW) and in vitro blood (haematocrit up to 17%) in a 100-μm-square microchannel. All the measurements were made in the middle plane of the microchannel at a constant flow rate and low Reynolds number ( Re=0.025). The averaged ensemble velocity profiles were found to be markedly parabolic for all the working fluids studied. When comparing the instantaneous velocity profiles of the three fluids, our results indicated that the profile shape depended on the haematocrit. Our confocal micro-PIV measurements demonstrate that the root mean square (RMS) values increase with the haematocrit implying that it is important to consider the information provided by the instantaneous velocity fields, even at low Re. The present study also examines the potential effect of the RBCs on the accuracy of the instantaneous velocity measurements.

A203 Blood Cell Motions and Interactions in Microchannels

Detailed knowledge on the motions and interactions of individual blood cells flowing in microchannels is essential to provide a better understanding on the blood rheological properties and disorders in microvessels. This paper presents the ability of a confocal micro-PTV system to track red blood cells (RBCs) through a 100 μm circular glass microchannel. The technique consists of a spinning disk confocal microscope, high speed camera and a diode-pumped solid state (DPSS) laser combined with a single particle tracking (SPT) software (MtrackJ). Detailed measurements on the motions of RBCs were measured at different haematocrits (Hct). Our results show clearly that this technique can provide detailed information about microscale disturbance effects caused by the blood cells.1) Goldsmith, H.: Red cell motions and wall interactions in tube flow, Federation Proceedings, Vol. 30, No.5 (1971) pp. 1578-1588.2) Goldsmith, H. and Marlow J.: Flow behavior of erythrocytes. 11. Particles motions in concentrated suspensions of ghost cells, Journal of Colloid and Interface Science, Vol. 71, No. 2 (1979) pp. 383-407.3) Lima, R., et al.: Confocal micro-PIV measurements of three dimensional profiles of cell suspension flow in a square microchannel, Meas. Sci. Tech., Vol. 17, (2006) pp. 797-808.4) Lima, R., et al., In vitro confocal micro-PIV measurements of blood flow in a square microchannel: the effect of the haematocrit on instantaneous velocity profiles, J. Biomech., (in press).5) Abramoff, M., et al.: Image processing with lmageJ, Biophotonics International, Vol. 11, No. 7 (2004) pp. 36-42.6) Meijering, E., et al.: Tracking in Molecular Bioimaging, , IEEE Signal Processing Magazine, Vol 23. No. 3 (2006) pp. 46-53.