Toru Torii

Controlled formulation of monodisperse double emulsions in a multiple-phase microfluidic system

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.

Droplet formation in a microchannel networkPresented at the International Symposium on Microchemistry and Microsystems (ISMM 2001), Kawasaki, Japan, September 16?18, 2001.

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).

Research in autonomous agriculture vehicles in Japan.

Abstract Much research on automation in agriculture has been presented in recent years at the annual meetings of the Japanese Society of Agricultural Machinery (JSAM). This research has been performed in universities and government institutes, and by agricultural machinery manufacturers. Because of funding limitations, research in universities has concentrated on methodologies, such as navigation, sensing, and application of control theory. Development of a one dimensional image sensor, and application of neural networks and genetic algorithms, has taken place at Hokkaido University; vision guidance and fuzzy logic application at the University of Tokyo; an automatic follow-up vehicle has been developed at Kyoto University; and an automatic transport vehicle at Ehime University. At research institutes and manufacturers, with their greater financial freedom, more practical systems have been developed. A tilling robot and a driver-less air blast sprayer is being developed in the Bio-oriented Technology Research Advancement Institute (BRAIN); and an autonomous rice planter, a tillage robot and autonomous forage tractor in the research institute of the Ministry of Agriculture, Forestry, and Fishery (MAFF). Kubota Co. Ltd has developed autonomous rice planting and husbandry vehicles. In Asian countries an autonomous speed sprayer is under study in Korea and an autonomous power sprayer in Taiwan, but little research is performed elsewhere in Asia.

Optimal control of physiological processes of plants in a green plant factory

Abstract In a plant factory, optimal control for obtaining higher yield and better quality of plants is essential. A modern control technique using optimal regulators and an intelligent control technique using genetic algorithms were applied to the control of the physiological processes of plants. In modern control, the variation in diameter with light intensity was measured, and the ARMA model was identified using the least squares method. Optimal regulators with a Kalman filter were used to control the water status of plants. In the intelligent control, on the other hand, the neural network was used for the model identification of net photosynthetic rate as affected by intermittent drainage of a hydroponic solution, and then the genetic algorithm was used for optimization via model simulation. These control techniques were quite useful for the optimal control of the physiological processes of plants.

Formation of droplets using branch channels in a microfluidic circuit

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.

Chemical reactions in microdroplets by electrostatic manipulation of droplets in liquid mediaPresented at the International Symposium on Microchemistry and Microsystems (ISMM 2001), Kawasaki, Japan, September 16?18, 2001.

A microchemical reaction method involving microdroplets is proposed. Microdroplets are formed in a chemically stable medium on electric panel devices. These devices are substrates which have electrode arrays or electrode dots, and its surfaces are coated by an insulating film (such as Teflon or polypropylene) to prevent discharge and electrolysis of solutions. Microdroplets can be separately manipulated by a traveling electric field, which arises on applying a sequential voltage to the electrodes. Droplets moved smoothly at 1 Hz and voltage 400 V(0-p). Reagents were then put in droplets that were collided and coalesced, resulting in chemical reactions that included alkalization of phenolphthalein and the luciferin-luciferase reaction.

An apparatus for electric-field-induced protein crystallization

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.

Protein crystallization under an electric field

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.

Hyper alginate gel microbead formation by molecular diffusion at the hydrogel/droplet interface.

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.

A lithography-free procedure for fabricating three-dimensional microchannels using hydrogel molds

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.