Haruyuki Kinoshita

Laser sintering fabrication of three-dimensional tissue engineering scaffolds with a flow channel network

The fabrication of tissue engineering scaffolds for the reconstruction of highly oxygen-dependent inner organs is discussed. An additive manufacturing technology known as selective laser sintering was employed to fabricate a highly porous scaffold with an embedded flow channel network. A porogen leaching system was used to obtain high porosity. A prototype was developed using the biodegradable plastic polycaprolactone and sodium chloride as the porogen. A high porosity of 90% was successfully obtained. Micro x-ray CT observation was carried out to confirm that channels with a diameter of approximately 1 mm were generated without clogging. The amount of residual salt was 930 µg while the overall volume of the scaffold was 13 cm(3), and it was confirmed that the toxicity of the salt was negligible. The hydrophilization of the scaffold to improve cell adhesion on the scaffold is also discussed. Oxygen plasma ashing and hydrolysis with sodium hydroxide, typically employed to improve the hydrophilicity of plastic surfaces, were tested. The improvement of hydrophilicity was confirmed by an increase in water retention by the porous scaffold from 180% to 500%.

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.

Investigation of Micro Droplet Formation in a T-Shaped Junction Using Multicolor Confocal Micro PIV

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 interfacial geometry scanning, the relationship between flow structure of each fluid and interfacial geometry is clarified. It indicates that the gap between the tip of discontinuous flow and capillary wall, and interface area play an important role in the flow structure and shear stress on the interface.Copyright

Viscoelastic droplet dynamics under very low interfacial tension in a serpentine T-junction microchannel

Viscoelastic surfactant-laden droplets were generated in silicone oil using a microfluidic T-junction channel device and the droplets dynamics was studied. Surfactant can greatly lower the interfacial tension between the continuous phase fluid and the dispersed phase fluid, and also introduces elasticity to the aqueous solution. The droplets in the confined microchannel experience a steady shear by the continuous phase flow, showing distinct morphological evolvement from those under normal magnitude of interfacial tension and Newtonian fluid nature. It is found that under very low interfacial tension droplet fragmentation (or tail streaming) composing of tiny satellites occurs at the rear of droplet (or upstream of droplet). The production of tails seems to depend on the combination of the capillary number (Ca), flow rate ratio and fluid elasticity (described by Weissenberg number, Wi). This phenomenon demonstrates a new flow regime for aqueous micro-droplets which covered by mobilized, soluble surfactant, indicating such a tail streaming concerns not only the fluid dynamical process, but the properties of the dispersed phase fluid.

PIV measurement of pressure- and electrokinetically-driven flow in microchannels

A micro PIV system has been developed as a new diagnostic tool for micro scale flow and applied to the measurement of microchannel flow. The micro PIV system employs the incident-light fluorescent microscope system and utilizes high-power pulsed Nd:YAG lasers, a high-resolution CCD camera and 1 μm diameter fluorescent tracer particles. The velocity distributions of pressure-driven flow and pressure- and electrokinetically-driven flow in a microchannel were measured using the micro PIV system and the visualization of flow fields in a microchannel was demonstrated.

Visualization and Measurement of Flow-Induced Dynamic Motion of Red Blood Cells Using Tracking Confocal Micro-PIV System

RBC(Red Blood Cell)s have a biconcave shape with diameters of about 8 μm and thicknesses of about 2 μm like a capsule structure with highly deformable membrane. In arterioles having diameters of less than 100μm, the effect of RBCs becomes pronounced because the scales of the flow and the RBCs become similar. RBCs exhibit the axial migration [1] toward the center of blood vessel. The axial migration leads to non-Newtonian flow behavior such as decrease in flow resistance. The tank-tread motion [2] makes an important role for the axial migration and it is dependent on the shear rate of the surrounding flow, which ranges up to 500 s−1 in arteriole.Copyright

Biomolecular Nano-Flow-Sensor to Measure Near-Surface Flow

We have proposed and experimentally demonstrated that the measurement of the near-surface flow at the interface between a liquid and solid using a 10 nm-sized biomolecular motor of F1-ATPase as a nano-flow-sensor. For this purpose, we developed a microfluidic test-bed chip to precisely control the liquid flow acting on the F1-ATPase. In order to visualize the rotation of F1-ATPase, several hundreds nanometer-sized particle was immobilized at the rotational axis of F1-ATPase to enhance the rotation to be detected by optical microscopy. The rotational motion of F1-ATPase, which was immobilized on an inner surface of the test-bed chip, was measured to obtain the correlation between the near-surface flow and the rotation speed of F1-ATPase. As a result, we obtained the relationship that the rotation speed of F1-ATPase was linearly decelerated with increasing flow velocity. The mechanism of the correlation between the rotation speed and the near-surface flow remains unclear, however the concept to use biomolecule as a nano-flow-sensor was proofed successfully.(See supplementary material 1)

Visualizations of Viscoelastic Fluid Flow in Microchannels

Solutions of flexible high-molecular-weight polymers or some kinds of surfactant can be viscoelastic fluids. The elastic stress is induced in such viscoelastic fluids and grow nonlinearly with the flow rate and results in many special flow phenomena, including purely elastic instability in the viscoelastic fluid flow. The elastic flow instability can even result in a special kind of turbulent motion, the so-called elastic turbulence, which is a newly discovered flow phenomenon and arises at arbitrary small Reynolds number. In this study, we experimentally investigated the peculiar flow phenomena of viscoelastic fluids in several different microchannels with curvilinear geometry by visualization technique. The viscoelastic working fluids were aqueous solutions of surfactant, CTAC/NaSal (cetyltrimethyl ammonium chloride/Sodium Salysilate). CTAC solutions with weight concentration of 200 ppm (part per million) and 1000 ppm, respectively, at room temperature were tested. For comparison, water flow in the same microchannels was also visualized. The Reynolds numbers for all the microchannel flows were quite small (for solution flows, the Reynolds numbers were smaller than 1) and the flow should be definitely laminar for Newtonian fluid. It was found that the regular laminar flow patterns for low-Reynolds number Newtonian fluid flow in different microchannels were strongly deformed in solution flows: either asymmetrical flow structures or time-dependent vortical flow motions appeared. These phenomena were considered to be induced by the viscoelasticity of the CTAC solutions.Copyright

Development and Application of Micro-PIV System Using High-speed Confocal Scanner

We have developed a confocal micro-PIV system that enables us to measure and visualize the velocity field in a thin planar region of micro flows. The confocal slice images can be captured with up to 2, 000 fps using the high-speed laser-scanning confocal microscopy and a high-speed camera. We can measure the micro flow in the horizontal region of 240 μm x 180 μm with the in-plane resolution of 9.6 μm x 9.6 μm and the out-of-plane resolution of 1.9 μm using the present system. The confocal micro-PIV system is applied to the internal flow measurement of a small droplet that is transported in a square microchannel with the size of 100 μm x 100 μm. The result shows the fluid inside a droplet circulates three-dimensionally and intricately.

Micro PIV Measurement of Electroosmotic Flow

The paper focuses on electroosmotic flow in a microfabricated channel in order to investigate the characteristics of microscopic flow in a microchip. Electroosmotic flow in microchannels was measured using a micro PIV (particle image velocimetry) system that has been developed especially for micro scale flow. We also evaluated the effect of (ζ-potential of tracer particles and channel surface on the flow.