Takasi Nisisako

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).

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.

Capillary‐Assisted Fabrication of Biconcave Polymeric Microlenses from Microfluidic Ternary Emulsion Droplets

In this study, a simple capillary-based approach for producing biconcave polymeric microlenses with uniform size and shape from ternary emulsion droplets is presented. Monodisperse ternary emulsion droplets (0.6-4.0 nL) are produced which contain a photocurable segment of an acrylate monomer and two non-curable segments of silicone oil (SO) by using a microfluidic sheath-flowing droplet generator on a glass chip. The curvature radius of the interfaces separating the droplet segments, as well as the droplet size, and production rate can be flexibly varied by changing the flow conditions of the organic and aqueous phases. Subsequently, off-chip suspension photopolymerization yields non-spherical polymeric microparticles with two spherical concave surfaces templated by two SO segments at random positions. By ultraviolet light irradiation of ternary droplets with two SO segments trapped by the interior wall of a cylindrical microcapillary (internal diameter: 130 μm), biconcave microlenses can be produced with two spherical concave surfaces with a common lens axis. The produced lenses are suitable for use as optical diverging lenses.

Rapid preparation of monodispersed droplets with confluent laminar flows

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.

Preparation of Picoliter-Sized Reaction / Analysis Chambers for Droplet-Based Chemical and Biochemical Systems

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.

Separation of viable and nonviable mammalian cells using a deterministic lateral displacement microfluidic device

Here, we present a deterministic lateral displacement (DLD) microfluidic device that may be used for label-free, passive, and continuous separation of viable and nonviable mammalian cells. Cells undergoing apoptosis (programmed cell death) become smaller than normal viable cells due to shrinkage and fragmentation. We used this distinct difference in size to selectively isolate viable Jurkat cells from nonviable apoptotic cells and their remnants through a DLD array that is capable of size-based fractionation of microparticles. First, we calibrated our DLD devices by separating a mixture of larger (∼15-μm) and smaller (∼8- or ∼10-μm) polystyrene beads that emulated viable and nonviable Jurkat cells, respectively. We then demonstrated the separation of viable and nonviable Jurkat cells by introducing their heterogeneous suspensions into two DLD devices with different design parameters. In a DLD device with a 20-μm gap, we collected viable cells at 100 ± 0% capture efficiency (n = 3), at a capture purity of ...

Biconvex Polymer Microlenses with Tunable Imaging Properties Designed by Janus Droplet Microfluidics

This work presents a technique for fabricating biconvex polymer microlenses using microfluidics, and then evaluates their tunable optical properties. A glass microfluidic channel was employed to rapidly mass-produce nanoliter-sized biphasic Janus droplets, which consist of a biconvex segment of a photocurable monomer and a concave-convex segment of a non-curable silicone oil that contained a surfactant. Subsequent photopolymerization produces polymeric biconvex spherical microlenses with templated dual curvatures. By changing the flow-rate ratios of the photocurable and non-curable droplet phases in the microfluidic channel, the radii of curvature of the two lens surfaces and the thicknesses of the resultant microlenses can be varied. The resulting biconvex microlenses with different shapes were used in image projection experiments. Different magnification properties were observed, and were consistent with the properties estimated quantitatively from the geometrical parameters of the lenses.

Separation of main and satellite droplets in a deterministic lateral displacement microfluidic device

A microfluidic droplet generator (MFDG) normally produces satellite droplets through break-off from the main droplet because of the Plateau–Rayleigh instability, resulting in contamination and/or poor size distribution of the products. Thus, we herein demonstrate the continuous, passive, and size-based separation of main and satellite droplets using the deterministic lateral displacement (DLD) array method. For the purpose of this study, we designed and employed microfluidic devices comprised of an upstream symmetric flow-focusing MFDG and a downstream DLD array composed of polydimethylsiloxane (PDMS). Initially, we produced water-in-oil (W/O) droplets containing main droplets of ∼61.1 μm diameter in addition to satellite droplets of 1–30 μm diameter in a hydrophobic MFDG, and we report the successful separation of the main and satellite droplets through a single-step DLD array with a critical diameter (Dc) of 37.1 μm. Furthermore, we demonstrated the generation and separation of single-phase or biphasic (i.e. Janus or core–shell) oil-in-water (O/W) main and satellite droplets using a hydrophilic MFDG and a DLD array. Finally, in addition to the removal of main and satellite W/O droplets, we also fractionated satellite droplets of different sizes into three groups (i.e., 21.4, 10.1, and 4.9 μm average diameter) using a device with three-step DLD arrays each having different Dc values (i.e., 37.1, 11.6, and 7.0 μm).

Droplet Formation in a Microchannel on PMMA Plate

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.