Two-dimensional (2D) microdroplet arrays with indexed sample concentration gradients have been receiving considerable attention for high-throughput biological and medical analyses. However, the preparation of such an array by conventional methods mandates precise pipetting and/or pumping. In this paper, we introduce a method to spontaneously generate 2D-arrayed aqueous droplets using a well array, for which coarse pipetting is sufficient. The wells are connected in rows and columns via narrow channels. Aqueous solutions impregnated in the well array are split into droplets in every single well as a subsequently introduced immiscible solvent self-propagates and divides the solution at the channels. A concentration gradient of the samples can be formed across the connected solution in the well array; once droplets are generated, each droplet possesses a different sample concentration depending on its position in the array. We experimentally determined the optimal well dimensions and solvent species to obtain a high yield of droplet generation. We next demonstrated a 2D droplet array with a two-sample concentration gradient. Finally, the applicability of the system was demonstrated through a cell viability assay using a sample that induced apoptosis. We believe the proposed method contributes to simplification and miniaturization of the system to generate droplet arrays and thus is applicable to biological and medical analysis.

A self-folding method that can fold a thick (~10 μm) metal layer with a large curvature (>1 mm⁻¹) and is resistant to repetitive folding deformation is proposed. Given the successful usage of hinged origami/kirigami structures forms in deployable structures, they show strong potential for application in stretchable electronic devices. There are, however, two key difficulties in applying origami/kirigami methods to stretchable electronic devices. The first is that a thick metal layer used as the conductive layer of electronic devices is too hard for self-folding as it is. Secondly, a thick metal layer breaks on repetitive folding deformation at a large curvature. To overcome these difficulties, this paper proposes a self-folding method using hinges on a thick metal layer by applying a meander structure. Such a structure can be folded at a large curvature even by weak driving forces (such as those produced by self-folding) and has mechanical resistance to repetitive folding deformation due to the local torsional deformation of the meander structure. To verify the method, the large curvature self-folding of thick metal layers and their mechanical resistance to repetitive folding deformation is experimentally demonstrated. In addition, an origami/kirigami hybrid stretchable electronic device with light-emitting diodes (LEDs) is fabricated using a double-tiling structure called the perforated extruded Miura-ori.

We proposed a method to display an intermediate visual texture by spatial mixing. In addition to color information, the visual texture is an important element that characterizes the nature of an object’s surface. While the system to display various color information has well matured in engineering, there is no method to reproduce visual textures in ambient light. In our method, the matte and glossy surfaces are used as “primary visual textures”, and an intermediate visual texture is displayed by spatially mixing the primary visual textures. In this paper, we first quantified the visual texture of an object’s surface based on measured intensities of scattered and reflected lights. Next, based on the quantification, we evaluated spatially mixed surfaces consisting of two primary visual textures, an acrylic plate and a holed sheet of drawing paper, by changing the area proportion of the two primary visual textures. Finally, a sensory evaluation showed significant differences between each intermediate visual texture, and the results corresponded to a trend in the optical evaluation. This study illustrates that visual textures could be quantified based on the intensity of scattered and reflected light and reveals the applicability of our method to the display for intermediate visual texture.

Herein, I review our recent work toward developing methods for generating three-dimensional (3D) droplet arrays driven by capillarity. Microdroplet array-based systems are useful for bioassays and bioengineering because they require only small amounts of samples and reagents and provide the high throughput. Various methods have been developed for preparing droplet arrays, among which methods based on capillarity have attracted considerable attention owing to their simplicity. I and collaborators have developed such methods based on capillary flow, including a method for preparing droplet arrays via oil–water replacement. We recently proposed our own concept of “fluid–fluid interfacial energy driven 3D structure emergence in a micropillar scaffold (FLUID3EAMS)” and its application. FLUID3EAMS allows a 3D droplet (or hydrogel bead) array to be generated in a micropillar scaffold by passing a fluid–fluid interface through the scaffold. This approach is useful for applications requiring ordered or arrayed microdroplets in biosensors, biophysics, biology, and tissue engineering. This review is an extended version of the article “FLUID3EAMS: Fluid–Fluid Interfacial Energy Driven 3D Structure Emergence in a Micropillar Scaffold and Development in Bioengineering” published in Seibutsu Butsuri (vol. 62, p. 110–113, 2022).

Tis paper describes construction of DNA-logic gate and connecting DNA-OR gate with DNA-NOT gate. When voltage is applied between two droplets separated by bilayer lipid membrane (BLMs), DNA is translocated into the biological nanopore formed by membrane proteins in BLMs In this study, we assembled DNA-NOR gates using BLMs, membrane protein and DNA, applying fusion method and split-and-contact method. In DNA-NOR gate system, for example, in case of (0, 1), one input droplets contains DNA-X. Therefore, the DNA is detected in output droplet of OR gate after it translocated to center droplet by fusion method. After center and output droplet fuse in OR gate and output droplet is slid to input position of NOT gate, the DNA is translocated to center droplet containing DNA-Y. Since DNA-Y and DNA-X are complementary, these is hybridization in the same droplet. DNA don't exist in output droplet in NOT gate because Double-strand-DNA cannot pass the nanopore. Therefore, output is 0.