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Nanoparticle (NP) concentration is crucial for liquid biopsies and analysis, and various NP concentrators (NPCs) have been developed. Methods using ion concentration polarization (ICP), an electrochemical phenomenon based on NPCs consisting of microchannels, have attracted attention because samples can be non-invasively concentrated using devices with simple structures. The fabrication of such NPCs is limited by the need for lithography, requiring special equipment and time. To overcome this, we reported a rapid prototyping method for NPCs by extending the previously developed hydrogel molding method, a microchannel fabrication method using hydrogel as a mold. With this, we fabricated NPCs with both straight and branched channels, typical NPC configurations. The generation of ICP was verified, and an NP concentration test was performed using dispersions of negatively and positively charged NPs. In the straight-channel NPC, negatively and positively charged NPs were concentrated &gt, 50-fold and &gt, 25-fold the original concentration, respectively. To our knowledge, this is the first report of NP concentration via ICP in a straight-channel NPC. Using a branched-channel NPC, maximum concentration rates of 2.0-fold and 1.7-fold were obtained with negatively and positively charged NPs, respectively, similar to those obtained with NPCs fabricated through conventional lithography. This rapid prototyping method is expected to promote the development of NPCs for liquid biopsy and analysis.

We herein report a method for the preparation of a glass microchannel capable of forming multiple emulsion droplets (i.e., water-in-oil-in-water and oil-in-water-in-oil) by locally controlling the wettability of the glass microchannel. Production of multiple emulsion droplets using a glass microchannel requires partial control of its wettability using a method that consists of two steps: (1) hydrophobization of a whole glass microchannel by filling the microchannel with octadecyltrichlorosilane (OTS) solution, and (2) local hydrophilization of the OTS-treated glass microchannel by exposure to ultraviolet light through a mask. However, conditions for the preparation of OTS-SAMs for controlling microchannel wettability and subsequent multiple emulsion droplet formation have not yet been reported. In this study, we investigated the conditions required to form multiple emulsion droplets and demonstrated formation of multiple emulsion droplets using a treated glass microchannel with multiple junctions. The glass microchannel prepared according to this method was able to form various aqueous and organic droplets due to its resistance to swelling.

We describe the behavior of droplet formation within 3D cross-junctions and 2D T-junctions with various cross-sectional geometries that were manually fabricated using the hydrogel-molding method. The method utilizes wire-shaped hydrogels as molds to construct 3D and 2D microchannel structures. We investigated the flow patterns and droplet formation within the microchannels of these microfluidic devices. Despite being fabricated manually, the microchannels with 3D cross-junctions and 2D T-junctions were reproducible and formed highly monodispersed droplets. Additionally, the sizes of the droplets formed within the microchannels could be predicted using an experimental formula. This technique of droplet formation involves the use of a device fabricated by hydrogel molding. This method is expected to facilitate studies on droplet microfluidics and promote the use of droplet-based lab-on-a-chip technologies for various applications.

We report a novel technique to fabricate alginate–TiO2 composite particles with densely packed TiO2 nanoparticles. Using a microfluidic device, monodisperse sodium alginate droplets containing low-density TiO2 nanoparticles (1 or 5 w/v%) were formed in the oil phase. The sodium alginate droplets formed in the oil phase were subsequently placed on a Ca2+-loaded agarose-gel plate to induce shrinkage by water removal (from the droplets to the Ca2+-loaded agarose-gel plate) and gelation by Ca2+ transport (from the Ca2+-loaded agarose-gel plate to the droplets). Thus, the produced alginate–TiO2 composite particles containing densely packed TiO2 nanoparticles were significantly smaller than the microchannel. We also investigated the optimal conditions to successfully produce spherical composite particles by varying the oil phases, surfactants, calcium concentrations and gel strength of the agarose-gel plate. Moreover, our method could decrease the probability of channel clogging that often occurs when a colloidal suspension (e.g., nanoparticles) is used as the dispersed phase. This method facilitates the stable production of monodisperse alginate–inorganic composite particles for a wide range of applications.

We describe a simple and robust technique for fabricating monodisperse Janus hydrogel beads with magnetic anisotropy smaller than the microchannel used to produce them.

We present a lithography-free procedure for fabricating intrinsically three-dimensional smooth-walled microchannels within poly(dimethylsiloxane) (PDMS) elastomer using hydrogel molds. In the fabrication process, small pieces of agarose gel ("wires" or "chips") are embedded in uncured PDMS composite, arranged in the shape of the desired microchannels, and used as molds to form the microchannels. The point of the process is that molds for creating junctions of microchannels such as T-junctions or cross-junctions can be robustly formed by simply grafting gel wires in uncured PDMS composite without using adhesive agents. The technical advantage of this method is that three-dimensional microstructures such as microchannels with circular cross sections, three-dimensionally arranged junctions or interchanges of microchannels can be flexibly designed and fabricated with a straightforward procedure without the need for any specialized equipment or layer-by-layer assemblage processes. This method provides a low-cost, green procedure for fabricating microfluidic devices and promises to make microfluidic processes more accessible and easy to implement in a variety of scientific fields.

In this study, we report the mass production of monodisperse emulsion droplets and particles using microfluidic large-scale integration on a chip. The production module comprises a glass microfluidic chip with planar microfabricated 16-256 droplet-formation units (DFUs) and a palm-sized stainless steel holder having several layers for supplying liquids into the inlets of the mounted chip. By using a module having 128 cross-junctions (i.e., 256 DFUs) arranged circularly on a 4 cm x 4 cm chip, we could produce droplets of photopolymerizable acrylate monomer at a throughput of 320.0 mL h(-1). The product was monodisperse, having a mean diameter of 96.4 microm, with a coefficient of variation (CV) of 1.3%. Subsequent UV polymerization off the module yielded monodisperse acrylic microspheres at a throughput of approximately 0.3 kg h(-1). Another module having 128 co-flow geometries could produce biphasic Janus droplets of black and white segments at 128.0 mL h(-1). The product had a mean diameter of 142.3 microm, with a CV of 3.3%. This co-flow module could also be applied in the mass production of homogeneous monomer droplets.

In order to form large micro-droplet-arrays, we have developed a device that can merge and transport microdroplets in two directions. Transportation of droplets is performed by electrostatic actuation technique. The speciality of this method is that it uses only one electrode panel, based on standard printed circuit board (PCB), and in it, only 18 independent controls are needed. We have also developed disposable plastic films cards, which can substantialy reduce the development cost because the actuation chip has been separated into two parts: a fixed electrode panel and a less costly removable card. The droplets array is formed and analyzed in the card.

New methods for improving the quality of protein crystals are always being sought. Electric-field-induced protein crystallization is one of them. A few devices have already been developed. We conducted a series of experiments for several years and fabricated many electrode panels to realize a device for electric-field induced protein crystallization for the microbatch method. The review mainly deals with the application of the various devices that have so far been reported in the literature on the subject, including an overview of the work that has already been conducted. The factors affecting the electric-field-induced protein crystallization are also discussed.

In this paper, a method for fabricating a microfluidic valve made of polydimethylsiloxane (PDMS) using a rapid prototyping method for microchannels through hydrogel cast molding is discussed. Currently, the valves in microchannels play an important role in various microfluidic devices. The technology to prototype microfluidic valves rapidly is actively being developed. For the rapid prototyping of PDMS microchannels, a method that uses a hydrogel as the casting mold has been recently developed. This technique can be used to prepare a three-dimensional structure through simple and uncomplicated methods. In this study, we were able to fabricate microfluidic valves easily using this rapid prototyping method that utilizes hydrogel cast molding. In addition, we confirmed that the valve displacement could be predicted within a range of constant pressures. Moreover, because microfluidic valves fabricated using this method can be directly observed from a cross-sectional direction, we anticipate that this technology will significantly contribute to clarifying fluid behavior and other phenomena in microchannels and microfluidic valves with complex structures.

This paper reports the preparation of encapsulated particles as models of cells using an alternating droplet generation encapsulation method in which the number of particles in a droplet is controlled by a microchannel to achieve one-to-one encapsulation. Using a microchannel in which wettability is treated locally, the fluorescent particles used as models of cells were successfully encapsulated in uniform water-in-oil-in-water (W/O/W) emulsion droplets. Furthermore, 20% of the particle-containing droplets contained one particle. Additionally, when a surfactant with the appropriate properties was used, the fluorescent particles within each inner aqueous droplet were enclosed in the merged droplet by spontaneous droplet coalescence. This one-to-one encapsulation method based on alternating droplet generation could be used for a variety of applications, such as high-throughput single-cell assays, gene transfection into cells or one-to-one cell fusion.

A new scheme for the polymer beads production using a microfluidic technique is described. This technique is based on the fact that droplets formation at a junction in microchannels is caused by shear stress acting on the dispersed-phase flow by the continuous-phase flow. The Reynolds number in a microchannel was very low which indicated the flow in the microchannel was laminar, therefore, uniform droplet formation was generated. The diameter of the droplets is widely varied from 50% to 300% to the diameter of the dispersed phase flow. Various monomers were used as a dispersed phase, and aqueous solution of polyvinyl alcohol as a continuous phase. Droplets produced in the microchannel were introduced from the drain to the server, and then polymerized by the thermal polymerization method or photo polymerization method. The droplet diameter was monodisperse with CV of less than 5%. Various polymer beads were produced by changing the geometry of the microchannel structure. By using this technique, two colored polymer beads, with different electrical potential for the electronics paper, were produced. We are now approaching to the mass production of the two colored polymer beads which is used for the manufacturing of electronic papers.

A microfluidic device having both hydrophobic and hydrophilic components is exploited for production of multiple-phase emulsions. For producing water-in-oil-in-water (W/O/W) dispersions, aqueous droplets ruptured at the upstream hydrophobic junction are enclosed within organic droplets formed at the downstream hydrophilic junction. Droplets produced at each junction could have narrow size distributions with coefficients of variation in diameter of less than 3%. Control of the flow conditions produces variations in internal/external droplet sizes and in the internal droplet number. Both W/O/W emulsions (with two types of internal droplets) and oil-in-water-in-oil emulsions were prepared by varying geometry and wettability in microchannels.

A novel technique is described for preparing multiple polymeric microspheres of the same size. A monodisperse droplet suspension of an acrylic monomer was prepared in a T-shaped microchannel, and particles of accurately the same size were produced by subsequent polymerization. The droplet/particle size was varied flexibly in the range of diameters 30–120 μm by changing the flow conditions in a microfluidic device. The resulting products have a coefficient of variation (CV) below 2%. A diagram of the flow parameters showed a clear region in which monosized drops were formed successfully. Furthermore, using another microfluidic device, hemispherically colored acrylic microspheres of 90–190 μm in diameter were engineered with a coefficient of variation of less than 1%.

To develop a rapid bacterial testing device, a microfluidic PCR device was designed. We simulated temperature distribution in a microchannel, and measured the temperature control from thermoelectric elements. In addition, we fabricated and evaluated the microfluidic pneumatic valve device which is one of the fundamental elements on our PCR device. As a result, because the PCR temperature distribution along the microchannel was visualized, the thermoelectric elements could be controlled on the basis of the result. Fabricated pneumatic valve was also tested to control the fluid. These results allow one to fabricate microfluidic PCR device for rapid bacterial testing.

A new device has been fabricated for electric field-induced protein crystallization with the microbatch method. In conjunction with this, a specialized tray using inexpensive plastic film has been developed for economical set-up of the experiments. Crystallization can be conducted using AC or DC voltage.

We develop a novel technique for fabricating monodisperse Janus hydrogel beads with magnetic anisotropy smaller than the microchannel based on coagulation of Fe3O4 nanoparticles and shrinkage-gelation technique. This technique can avoid the problem of limits to the minimum biphasic droplet size due to the high risk of clogging, and the problem of a blurring boundary on fabricated Janus particles by convective mixing across the interface inside the biphasic droplets. Therefore, this technique has potential for the further development of electronic paper.

We report a simple method for forming monodispersed, uniformly shaped gel microbeads with precisely controlled sizes. The basis of our method is the placement of monodispersed sodium alginate droplets, formed by a microfluidic device, on an agarose slab gel containing a high-osmotic-pressure gelation agent (CaCl(2) aq.): (1) the droplets are cross-linked (gelated) due to the diffusion of the gelation agent from the agarose slab gel to the sodium alginate droplets and (2) the droplets simultaneously shrink to a fraction of their original size (100 μm in diameter) due to the diffusion of water molecules from the sodium alginate droplets to the agarose slab gel. We verified the mass transfer mechanism between the droplet and the agarose slab gel. This method circumvents the limitations of gel microbead formation, such as the need to prepare microchannels of various sizes, microchannel clogging, and the deformation of the produced gel microbeads.

Mass culture of plant cell and tissues in a bioreactor are widely used for production of plant metabolites or seedlings. Packed Cell Volume (PCV) and Optical Density (OD) are used for off-line measurement, and Electric Conductivity (EC) and pH are used for on-line measurement of growth rate in bioreactors. In these measurement, the samples are derived from a part of a reactor, and these sample may not indicate the actual status of bioreactor, because the growth rate may change in height or radius of bioreactor.An ultrasonic technique was used to measure the growth rate in a bioreactor.The material used were plant cell of Rice plant (Oryza sativa), and adventive root of Atropa belladonna. The frequency of ultrasonic sensors were 0.5, 1, 2, 3, 5, and 7 MHz. It was found that the attenuation of ultrasonic wave propagated through the bioreactor had linear relation with the growth rate and that the stronger attenuations were measured in higher frequencies. The velocity of waves were almost constant with the growth rate. A simple model using a wave equation was used to simulate the attenuation of ultrasonic wave in the bioreactor, and the results showed good agreement with the experiment. The ultrasonic wave can propagate across the bioreactor, and it seems that the results correspond to the actual status of the bioreactor.

A method is given for generating droplets in a microchannel network. With oil as the continuous phase and water as the dispersed phase, pico/nanoliter-sized water droplets can be generated in a continuous phase flow at a -junction. The channel for the dispersed phase is 100 microm wide and 100 microm deep, whereas the channel for the continuous phase is 500 microm wide and 100 microm deep. For given experimental parameters, regular-sized droplets are reproducibly formed at a uniform speed. The diameter of these droplets is controllable in the range from 100-380 microm as the flow velocity of the continuous phase is varied from 0.01 m s(-1) to 0.15 m s(-1).

In this work, we describe the synthesis of novel electrically and magnetically dual-driven Janus particles for a handwriting-enabled twisting ball display via the microfluidic technique. One hemisphere of the Janus particles contains a charge control agent, which allows the display color to be controlled by applying a voltage and superparamagnetic nanoparticles, allows handwriting by applying a magnetic field to the display. We fabricated a twisting ball display utilizing these Janus particles and tested the electric color control and handwriting using a magnet. As a result, the display was capable of permitting handwriting with a small magnet in addition to conventional color control using an applied voltage (80 V). Handwriting performance was improved by increasing the concentration of superparamagnetic nanoparticles and was determined to be possible even when 80 V was applied across the electrodes for 4 wt. % superparamagnetic nanoparticles in one hemisphere. This improvement was impossible when the concentration was reduced to 2 wt. % superparamagnetic nanoparticles. The technology presented in our work can be applied to low-cost, lightweight, highly visible, and energy-saving electronic message boards and large whiteboards because the large-size display can be fabricated easily due to its simple structure.

A bubble-based chemical reaction/analysis system is proposed that uses electrostatic micromanipulation. Micro/nanoliter-sized bubbles are set in a liquid layer below an electrode array device. The micro bubbles are manipulated smoothly by the electrostatic force generated by the electrode array. A chemical reaction between two gas reagents, exemplified by 2NO+O/sub 2//spl rarr/2NO/sub 2/, has been demonstrated.

We study the formation of micro droplets in confluent two-phase flows in a microfluidic system. Instability at the interface of two immiscible liquids undergoing laminar flow generates micro droplets of highly uniform size. Under high shear stress the droplets form rapidly, and more than 2000 droplets can be prepared of similar size. Droplet size can be controlled by varying the flow conditions. Also, the effect of tension at the interface is studied by comparing results from PMMA/glass devices. Monodisperse polymeric microspheres were successfully obtained by polymerization of prepared monomer droplets.

We have developed a new method to measure the hydraulic conductivity of cell membrane (L/sub p/), based on the principle that two liquids flow in laminar flow though relatively narrow space. The developed method has advantages that the number of the required cell sample is only one, and accurate measurement can be made as compare with the conventional method.

Feasibility study of PCR using electrostatic manipulation of micro droplets is discussed. Adherence of droplets to the surface has been a difficult hindrance to overcome when controlling PCR solution in liquid medium. Different types of medium immiscible with the droplets are tested and n-octane enables electrostatic manipulation of PCR droplets. The concept of a novel micro PCR device is proposed.

This paper presents a new method for preparing micro droplets inside the liquid layer at a T-junction in a microchannel network. The relations between droplet size, flow speed, and channel size are studied. The droplet size is easily varied by changing the flow conditions in the microchannels. The size distribution of the resulting droplets is very narrow.

A novel method is presented for preparing micro droplets using branch structures in a microfluidic device. This method enables the rapid preparation of droplets with extremely narrow size distribution, and flexible control of droplet size was achieved by changing flow conditions in microchannels. The relations between the droplet size, flow condition, and channel size are studied.

Reducing water loss from vegetables is important to maintain freshness. The hydraulic conductivity coefficient (Lp) of cell membranes is indispensable to analyze the movement of water from cells, which leads to wilting and low metabolic activity. To measure Lp, extracellular solution must be replaced quickly to apply osmotic stress to the cells; however, conventional methods take a relatively long time, which leads to noticeable errors. We therefore developed a new method to measure Lp based on the principle that two liquids exhibit laminar flow through a relatively narrow space, for example, a tube having a small inner diameter. A microchannel having a diameter of 1.4 mm was designed. The microchannel has two inlets, and the flow rate of solution at each inlet can be used to determine the volume of each solution occupying the microchannel. Hence, an extracellular solution of protoplast fixed in a microchannel can be changed instantaneously by changing the flow rate of the solution. The Lp values of barley cotyledon and spinach leaf protoplasts were measured by both the developed method and a conventional method. Lp values measured by the conventional method were lower than those measured by the newly developed method. The developed method also showed less scattering in the measured Lp values because the errors caused by the experimental operation were reduced. In addition, the difference in values measured by both methods was examined by error estimation, and the values obtained by the new method were determined to be valid. With this method, the time delay to replace the extracellular solution was negligible and Lp was obtained without any error being caused by the time required for replacement.

A method for generating droplets in a microchannel network has been studied. Using oil as continuous phase and water as dispersed phase, nanoliter-sized water droplets are generated in the oil flow at a T-junction.

Reagent and samples were put in micro capsules which were surrounded by chemically stable medium. They were manipulated independently by electric field, collided with each other, and mixed. Chemical reaction was caused in mixed capsules.

An apparatus which applies the ultrasonic technique was constructed to measure the diffusion coefficients of sodium chloride in corn starch sols. At a frequency of 1 MHz, the ultrasonic velocity was observed to increase proportionally with the concentration of sodium chloride and of starch. By employing the ultrasonic technique, it becomes possible to detect the concentration changes continuously and nondestructively. Furthermore, the accurate diffusion coefficient of substances in fluids may be obtained. The diffusion coefficients of sodium chloride in 1%, 3% and 5% corn starch sols were obtained as 1.12, 1.07 and 0.94 x 10-5 cm2/s, respectively.

The intermediate state between microdroplets and microfluidics in two immiscible fluids is described. It was found that Y-shaped two-phase flow is formed with a stable liquid/liquid interface at a cross junction in a hydrophilic microchannel. A velocity vector map, obtained by microparticle image velocimetry, reveals the Y-shaped flow consists of aqueous phase flow along the edge of the channel and an acrylate monomer phase flow penetrating the center. The transition from the Y-shaped flow to other flow patterns can be characterized by a state diagram that depends on the capillary number and the Weber number of each injecting phase.

This paper gives an overview of our recent work on the use of microfluidic devices to formulate double emulsions. Key issues in the controlled encapsulation of highly monodisperse drops include: (a) regular periodicity in the formation of micro droplets due to the interplay between viscous shearing and interfacial tension in low Reynolds number streams; (b) serially connected hydrophobic and hydrophilic microchannels to form aqueous and organic drops consecutively. Water-in-oil-in-water emulsions and oil-in-water-in-oil emulsions can both be produced by reversing the order of hydrophobic and hydrophilic junctions. Alternating formation of aqueous droplets at a cross junction has enabled the production of organic droplets that encase two aqueous droplets of differing compositions.