Published papers

In this work, we propose a new approach to tactile research using natural language processing of archival word corpus as the database. Tactile perception, or assessment of surfaces, is recognized as a language. Thus, by extracting touch-related words and sentences from a text corpus and learning their relationships, we can ultimately learn how humans perceive surfaces. We selected 6 adjectives and 42 onomatopoeias in Japanese as our tactile words. The adjectives represent physical properties, such as roughness and hardness, while onomatopoeias, such as “zara-zara” and “tsuru-tsuru,” are widely used to describe surfaces in Japanese and can correspond to both physical texture cognition and affective cognition. First, using natural language processing of word corpora, we successfully mapped the onomatopoeias with respect to the 6 adjectives, which matched well with the results based on an enquete-based survey. This verified the effectiveness of natural language processing for tactile research. In addition, principal component analysis revealed new tactile dimensions based on onomatopoeias, which we presumably assessaffective tactile dimensions. The proposed approach using natural language processing of archival text databases can provide a large number of datasets for tactile research and culminate in new findings and insights.

Copyright© (2018) by Chemical and Biological Microsystems Society.All rights reserved. This paper demonstrates a three-dimensional microfluidic device for sequence-controlled mixing of solutions. First, we designed and fabricated the device. The major characteristics of the device are pumpless and having three-dimensional network and mechanical components (rotate and translate) to control the fluidic paths. We injected four different solutions to each inlet of the device and generated the mixed three solutions in the designated orders by rotating and sliding the device. Successful parallel and sequential mixing was verified.

Copyright © (2018) by Chemical and Biological Microsystems Society. All rights reserved. Here we report an improved μTAS based on electrochemical measurements and microbeads sorting for screening of NAD(P)-dependent oxidoreductases. By using this system, we measured the activity of model enzymes immobilized on microbeads by detection of NADH with a boron-doped diamond (BDD) electrode in each compartment (∼30 nL) of the microfluidic system. Then, we recovered the magnetic microbeads or the droplets containing genes of enzymes with higher activity by magnetophoretic or dielectrophoretic sorting, respectively. Our μTAS should be useful for directed evolution of various NAD(P)-dependent oxidoreductases with high activity and stability in the future.

© 2020 IEEE. We have developed a novel on-substrate composition patterning process of room-temperature liquid metal alloys via a simple two-step method: 'coat pop'. This work present for the first time the integration of a single or several noble metals (Au, Ag or Cu) on Ga-based liquid metal droplets on a single substrate, by using a spontaneous chemical reaction then simple mechanical compression, to form biphasic and liquid composition patterns. The controllable deposition of noble metals encapsulation patterns and formation of several interfaced conductive biphasic intermetallic alloys on a single substrate were successfully demonstrated.

© 2020 IEEE. This paper proposes a technique to reconstitute a lipid bilayer membrane by injecting an air bubble onto the raptured spot. Our group has been studying the artificial bilayer that can host membrane proteins and can be a fundamental to analyze their functions. The only drawback of the lipid bilayer formed at the interface of two water-in-oil droplets is its sustainability, namely, the bilayer often collapses and the droplets merges by the disturbance like self-exerted oscillation or sloshing. To overcome this issue, the newly proposed technique utilizes a bubble at approximately 4μL in volume. When the bubble is injected and retracted, the new artificial bilayer is reconstituted. The major advantage of this technique is the in-situ reconstitution of the bilayer during the electrical measurement of the membrane proteins. The proposed technique was successfully verified by confirming the emergence of nanopore membrane proteins.

© 2019 IEEE. This paper reports the EEG-Hat, the hat-type EEG device with candle-like dry microneedle electrodes. Current wearable EEG devices have two major problems; 1) no adjustability to every participant and 2) no ability to measure EEG at hairy part. If these problems are solved, health care technologies in daily life will be developed drastically. The EEG-Hat potentially solves these problems. This device can adjust the electrodes to different size and shape of human head. This device has shutter-like structures to separate hair, so using this device, it is possible to measure EEG without separating hair by hand. First, we quantified the force to press the electrodes and the amount of separating hair. Then, the EEG-Hat fabricated based on the findings successfully measured EEG from 3 hairy parts without manual separation.

© 2020 IEEE. This paper reports a simple viscometer, whose principle utilizes the relationship between liquid viscosity and the suction speed in a tube. The proposed viscometer is composed of an air chamber and a glass tube. A steel ball is attached to the silicone membrane of the chamber and an electromagnetic magnet is used to provide the volume change. A MEMS pressure sensor element is attached to the chamber to measure its pressure change. When a step-response volume change is applied, the chamber pressure decreases so that the liquid sticking to the tube gradually ascends at a speed depending to the viscosity. Thus, the viscosity can be calculated by measuring the gradient of the pressure change. The proposed method can be applied to micropipettes so that viscosity is easily measured with a simple device.

© 2019 IEEE. Droplet interface bilayer (DIB) networks are expected to lead to tissue-like materials that can be designed from single droplets. Although various functions, such as sensors or computing, have been implemented into DIB networks, there remains a challenge in terms of configurability of constituent droplets in three-dimensional (3D). In this paper, we construct 3D DIB networks with defined droplet positions. We prepared 2D droplet arrays in paper-like substrates based on a method that we previously reported. Vertical stacking of the 2D arrays resulted in DIB formation between layers, i.e., a 3D DIB network.

© 2019 The Royal Society of Chemistry. A novel biphasic sub-micrometer Au-AuGa2/liquid metal framework, consisting of solid nanoparticles encapsulating liquid metal (LM) droplets, is introduced. By utilizing oxide-free galvanic replacement of a Ga-alloy LM with alkaline KAuBr4, the controllable process of gold-based encapsulation of individual sub-micrometer LM droplets capped with polyvinylpyrrolidone, lysozyme or sodium alginate is demonstrated. The morphology, structure and composition of the encapsulated droplets are characterized in-depth via scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. For the first time, the existence of two kinetic regimes leading to the controllable synthesis of either intermetallic AuGa2 or Au nanoparticles to encapsulate LM droplets is highlighted via the study of the evolution of the pH of the reaction medium. The as-formed biphasic sub-micrometer Au-LM frameworks demonstrate moderate stability in an aqueous environment and formidable structural and chemical stability in ambient air at room temperature. The encapsulation process can be adapted to the micro-patterning of LM droplet surfaces to produce conductive Au-encapsulated LM droplets then sintered to recover LM lines, while the sub-micrometer Au-LM droplets can be reintegrated onto larger LM surfaces and volumes to create multi-metallic and multi-scale biphasic structures with controllable electrical properties. The adaptability of the encapsulation process to the macro-, micro- and nanoscale of liquid metal features with a wide range of surfactants could in principle allow its use in various systems and applications.

© 2019 IEEE. We introduce microparticle filters with temperature tuneable size cut-off and surface energy. At room temperature, the filter cut-off is 164 \pm 23\ \mu \mathrm{m}, and the filter is water-absorbing/oil-repelling (hydrophilic). At 50 °C, the filter cut-off is 695\pm 31\ \mu \mathrm{m}, and the filter is oil-absorbing/water-repelling (hydrophobic).

© 2019 IEEE. In this study, we developed a flexible tactile sensor that scans the surface to detect the stiffness distribution. Note that the sensor does not need to know the displacement or strain of the target surface.Endoscopic palpation is a promising technology to detect tumors that have larger stiffness than normal tissues. The stiffness can be deduced by acquiring the load applied and the displacement, whereas the displacement or strain of the tissue is difficult to obtain given that endoscope has an arbitrary shape when in use and the tissue surface is not flat. In this study, we propose a new stiffness sensor composed of four strain gauges with different Young's modulus to detect the target without measuring the strain. The developed flexible sensor uses encapsulated liquid metal as the electrodes and can scan the surface.

© 2018 IEEE. Coagulation of blood inside the implanted medical device is quite a critical problem to limit the lifetime. In this paper, we propose a microfluidic blood separating device using curved and branched channels. It utilizes centrifugal force on curved flow and separates blood flow into blood cell rich and blood cell poor ones at the bifurcation. Though it cannot separate the plasma from blood cells completely, the blood with small concentrations of blood cells will have low coagulatibity and extend the lifetime of the implant medical device. The device does not require any external pumps or valves, i.e., the system does not need any power sources but the blood pressure. We conducted experiments with a titanium foil which contacted to human whole blood with different hematocrit values for 7 days. The device was experimentally characterized with respect to the channel design. The former experiments suggested that lower concentration of blood cells helps avoiding blood coagulations, and the latter showed that the separation by our device is mainly affected by the flow rate and channel curvature.

© 2019 Japan Institute of Electronics Packaging. This paper describes investigation of the brain activity in an adapting process to inversion vision through electroencephalogram (EEG). In particular, we used Candle-like microneedle electrodes, which does not require any preparation for measuring high-quality EEG. Note that conventional wet electrodes require abrasion of stratum corneum and application of electrolyte paste as preparation for measurement of EEG and they give discomfort to subjects and take time for experimenters. In our previous study, the eye movement during the adapting process was measured and the progress of the process was successfully captured. In this study, we measured EEG during the pointing task under an inverse vision state to correlate the perceptual learning with EEG. We discovered that High β wave, Low γ wave and Mid γ wave had strong correlation with the process of adapting to inversed vision.

© 2019 Japan Institute of Electronics Packaging. Our group has been developing implantable artificial dialysis system to decrease burden of chronic kidney disease patients. To evaluate the device, long-Term in vivo experiments are mandatory. However, we need to complete the detailed design of the devices prior to the long-Term tests, which range from the temporal change of the device performance to time to surgical procedures. To do so, we need to conduct mid-and long-Term in vivo experiments for multiple times to acquire sufficient information. It is useful to use small animals, such as rats, for in vivo experiment. However, there is no prior work that discusses mid-and long-Term coagulation ability control in small animals. In this study, we investigated the heparin administration to manage the coagulability. A simplified device was connected to SD rats under coagulability control and the blood coagulation in the device was characterized. And succeeded in blood clotting inhibition for 48 hours

© 2018 IEEE. This paper reports successful measurement of even-related potential (ERP) using candle-like dry microneedle electrodes, which can acquire high-quality electroencephalogram (EEG) from hairy parts without any pretreatment. In our previous work, we successfully measured spontaneous EEG activity and its application to assess the stress state of the subjects. ERPs originate from electrophysiological response to stimulus and are one of the most important indices to capture the cognitive and sensory activities. In this work, using the candle-like dry microelectrodes, we demonstrate successful measurement of ERPs elicited by oddball tasks. Two oddball tasks using pure tone stimuli and speech stimuli were assigned to the subjects, where EEG was acquired from the parietal region (Cz in international 10-20 system). Note that no pretreatment, such as removal of hairs and abrasion of the scalp, was applied. As a result, P300 and mismatch negativity (MMN) were successfully measured in the both oddball tasks from the averaged EEG after the stimuli. Based on these results and given the attractive natures of the candle-like dry microneedle electrodes; they do not need any skin treatment and conductive gels and they can measure EEG from the hairy parts, the developed electrodes will accelerate cognitive neuroscience research using ERPs.

© 2019 IEEE. This work designs and demonstrates the lipid bilayer-based ultra-sensitive biosensor capable of short-time detection in a quantitative manner, which is achieved by connecting multiple sensor elements in parallel.Artificial cell membranes with functional membrane proteins can form sensitive/selective biosensors. But the sensors suffer lengthy detection time at low concentration of analytes because the sensing mechanism relies on stochastic phenomena.In this work, we connected independent membrane sensors in parallel, where the ionic current through the multiple membranes was monitored by a single detector. With this format, the detection time is shortened based on the number of the array and the sensing can be quantitative. We developed a quad sensor assembling four membranes in parallel, and examined detection time of a single membrane sensor, the quad sensor, and four parallel quad-sensors. 1-Gω resistor was installed in series with each membrane to avoid overload current caused by membrane rupture. The results showed significant improvement in the detection time and deviation by the parallelization, which promises quantitative monitoring with the stochastic sensor.

© 2019 IEEE. We demonstrate a thermal sensation display that can present various thermal sensation by varying the thermal conductivity of the display. Thermal sensation, i.e., cold/cool/warm/hot, is one of the major tactile sensations and needs to be further investigated to advanced VR/AR systems. Although many reports on the tactile displays present hot/cold surfaces by changing the surface temperature, the proposed display is the first one that can control thermal conductivity. The device contains liquid metal, whose contact to the top titanium plate determines the thermal conductivity of the device and thus, the thermal sensation presented to the users. This device can be a good platform for the study of thermal sensation.

© 2018 IEEE. This paper describes a microfluidic device to continuously produce a hydrogel microtube using triple-coaxial flow. In our prior work, double-coaxial flow was used to produce hydrogel microtubes, though continuous and mass production was a challenge. In this work, we also demonstrate bioremediation using the microtubes that encapsulate microbial suspension. The microenvironment created by the microtubes enabled efficient purification of aqueous sample solution and in addition, the microbes are maintained inside the microtube and are easily collected without contaminating the solution. The proposed technology can be applied to any types of microbes and can be of great benefit for various microbial processes.

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Microfluidic systems have been developed for patterning single cells to study cell–cell interactions. However, patterning multiple types of cells to understand heterogeneous cell–cell interactions remains difficult. Here, it is aimed to develop a cell-trapping device to assemble multiple types of cells in the well-controlled order and morphology. This device mainly comprises a parylene sheet for assembling cells and a microcomb for controlling the cell-trapping area. The cell-trapping area is controlled by moving the parylene sheet on an SU-8 microcomb using tweezers. Gentle downward flow is used as a driving force for the cell-trapping. The assembly of cells on a parylene sheet with round and line-shaped apertures is demonstrated. The cell–cell contacts of the trapped cells are then investigated by direct cell–cell transfer of calcein via connexin nanopores. Finally, using the device with a system for controlling the cell-trapping area, three different types of cells in the well-controlled order are assembled. The correct cell order rate obtained using the device is 27.9%, which is higher than that obtained without the sliding parylene system (0.74%). Furthermore, the occurrence of cell–cell contact between the three cell types assembled is verified. This cell-patterning device will be a useful tool for investigating heterogeneous cell–cell interactions.

© 2018 IEEE. This paper presents a precise sampling microstructure formed as a paper strip. We have been developing dialysis system that can be implanted into a human body as an artificial kidney. For the safe use of our artificial kidney, the patients' urine needs to be constantly monitored to detect the abnormal value of ion concentration essential for human life. We are conceiving the monitoring system based on sampling by a paper strip. In this study, we fabricated the strip consisting of slanted and interlocked micropillars for the sampling, known as synthetic microfluidic paper. The paper-like substrate can be fabricated with a well-controlled geometry and subsequently enables precise sampling. Through the conducted experiments, it was shown that synthetic microfluidic paper had better mechanical properties, showed more precision in sampling than paper filter as well as corresponding liquid holding capability to the paper filter. Our proposed paper-based sampling system is expected to lead to the development of minimally invasive ion monitoring system with quantitative sampling strip.