We previously established an automatic droplet‐creation technique that only required air evacuation of a PDMS microfluidic device prior to use. Although the rate of droplet production with this technique was originally slow (∼10 droplets per second), this was greatly improved (∼470 droplets per second) in our recent study by remodeling the original device configuration. This improvement was realized by the addition of a degassed PDMS layer with a large surface area‐to‐volume ratio that served as a powerful vacuum generator. However, the incorporation of the additional PDMS layer (which was separate from the microfluidic PDMS layer itself) into the device required reversible bonding of five different layers. In the current study, we aimed to simplify the device architecture by reducing the number of constituent layers for enhancing usability of this microfluidic droplet generator while retaining its rapid production rate. The new device consisted of three layers. This comprised a degassed PDMS slab with microfluidic channels on one surface and tens of thousands of vacuum‐generating micropillars on the other surface, which was simply sandwiched by PMMA layers. Despite its simplified configuration, this new device created monodisperse droplets at an even faster rate (>1000 droplets per second).

The fixation strengths between conventional/modified magnetic assemblies and denture base resins were evaluated using six alternative resins. Magnetic assemblies with three different undercut wings were prepared. Soft lining materials with added PMMA resin polymer, two photopolymerization denture relining resins, an experimental resin, and a temporary filling resin were used to fix the magnetic assemblies to the denture bases. As a control, a commercially available magnetic assembly without undercut wings and a conventional autopolymerized resin were also prepared. After surface treatments, the magnetic assemblies were fixed using fixation resins, and tensile strengths and attractive forces were measured using an autography. The experimental resin and the temporary filling resin showed retentive forces comparable to those of conventional autopolymerized resins. Although the experimental resin demonstrated satisfactory fixation strengths, it should be necessary to improve its mechanical strength. The temporary filling resin could be used as a permanent fixation material.

To form monodisperse water-in-oil droplets in a fully automated fashion, we fabricated a pumpless microfluidic device consisting of top and bottom polydimethylsiloxane slabs. All microstructures required for droplet formation were directly patterned on the surfaces of two polydimethylsiloxane slabs using CO2 laser micromachining, facilitating rapid fabrication of the current device. This device formed uniformly sized droplets (a coefficient of variation for droplet diameters of <4%) at a rate of ∼220 droplets/s.

In our recent study, we fabricated a pump/tube-connection-free microchip comprising top and bottom polydimethylsiloxane (PDMS) slabs to produce monodispersed water-in-oil droplets in a fully automated, fluid-manipulation fashion. All microstructures required for droplet production were directly patterned on the surfaces of the two PDMS slabs through CO2-laser micromachining, facilitating the fast fabrication of the droplet-production microchips. In the current extension study, we replaced the bottom PDMS slab, which served as a microfluidic layer in the microchip, with a poly(methyl methacrylate) (PMMA) slab. This modification was based on our idea that the bottom PDMS slab does not contribute to the automatic fluid manipulation and that replacing the bottom PDMS slab with a more affordable and accessible, ready-to-use polymer slab, such as a PMMA, would further facilitate the rapid and low-cost fabrication of the connection-free microchips. Using a new PMMA/PDMS microchip, we produced water-in-oil droplets with high degree of size-uniformity (a coefficient of variation for droplet diameters of <5%) without a decrease in the droplet production rate (~270 droplets/s) as compared with that achieved via the previous PDMS/PDMS microchip (~220 droplets/s).

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