Published papers

Small oral-intake sensors are extremely effective in detecting diseases concerning the digestive system because those sensors enable remote monitoring of information in the body through oral intake. Conventional oral-intake sensors contain indigestible substances, such as batteries and cameras. Hence, if those sensors become lodged in the narrowed gastrointestinal tract, highly invasive procedures such as laparotomy are required for their removal. To solve this issue, edible digestible sensors with split-ring resonators (SRRs) have previously been proposed. The proposed digestible sensors use electromagnetic waves for measurement, however, the response of the electromagnetic wave of the digestible SRR sensor is anisotropic, resulting in the limitation of the direction of electromagnetic wave irradiation to the digestible sensor's attitude for acquiring the electromagnetic response. In this study, we propose a food-based edible monitoring device that responds isotropically to electromagnetic irradiation. The device consists of only ingredients: a cubic sugar substrate with an edible gold thin-film electrode on an edible starch sheet. The isotropic electromagnetic wave reflection characteristics and digestion properties in in vitro environment mimicking the gastrointestinal tract have been examined.

The stacking of monolayers to form a twisted bilayer has attracted attention because of the emergent properties of moiré patterns. However, the current process of forming twisted bilayers involves mechanically repeating the pick-up and restacking of monolayers, which is a nonscalable method. In this study, we developed a method for mass production of stacking twisted bilayers using the coalescence of unique droplets. The droplets were formed via the liquid-liquid phase separation phenomenon, in which droplets spontaneously form in a uniform solution. The droplets move and coalesce on the monolayers, inducing folding of the monolayer and enabling the mass production of twisted stacked bilayers.

This paper describes a micro-scale mapping of protein expression on endothelial tissue in an extracellular matrix (ECM)-based branched microchannel under mechanical stimuli. Our system mimics the heterogeneity in the distribution of complex mechanical stimuli applied to tissues in vivo by applying mechanical stimuli to a branched vascular model. We confirmed the up-regulation of gene expression levels in vascular endothelial cells(ECs) by stretch stress. We cultured ECs under complex mechanical stimuli, and visualized the distribution of mechanotransducer protein expression in the branched vascular model. We believe that our system could open a new door for the analysis of local cellular responses to mechanical stimuli.

This paper describes a stretchable extracellular matrix (ECM)-based in vitro endothelial vascular model with branched channels that can reproduce mechanically driven pulsatile flow. We imaged and analyzed the pulsatile flow at the branched points that are unique structures of blood vessels. The analysis revealed characteristic flow streams to the cultured endothelial cells near the branched points. We believe that our system would reveal the complex mechanical cellular response in blood vessels and enable the construction of mature in vitro vascular tissues.

This paper describes repeatable detection of Ag+ ions using a DNA aptamer-linked hydrogel biochemical sensor integrated with a microfluidic heating system. Biochemical sensors that respond to chemical compounds and produce detectable signals have a critical role in many aspects of modern society. In particular, the repeatable measurement of environmental information such as toxic substances including Ag+ ions could be expected to improve the environment. The DNA aptamer is an attractive candidate because of the stability and the selectivity of binding to chemicals. However, previous DNA aptamer biochemical sensors could not measure repeatedly because those sensors did not have initializing functions. To overcome this challenge, we proposed a DNA aptamer-linked hydrogel biochemical sensor integrated with the microfluidic heating system enabling repeatable detection of Ag+ ions. The binding Ag+ ions are dissociated by heating and flushing through the integrated microfluidic heating device. The DNA aptamer-linked hydrogel had the capability to detect a wide range of Ag+ ion concentrations (10−5–10 mM) including a toxic range for various aquatic organisms. Finally, we demonstrated the repeatable detection of the Ag+ ions. These results indicated that our proposed biochemical sensor is expected to use for long-term monitoring with high stability in ambient temperature and low power consumption.

This paper describes a pH sensor for soil monitoring that is composed of fully biodegradable materials in the soil. Our biodegradable pH sensor is composed of only two key elements: One is a magnesium electromagnetic antenna that dissolves in water, and the other is a protection layer of hydroxyapatite that decomposes in response to pH. This sensor works as an electromagnetic split-ring resonator (metamaterial) that reflects electromagnetic waves with specific frequency in GHz band, enabling in wireless remote sensing without any electric circuits or batteries. We demonstrated wireless pH detection of soil for aiming to realize an environmentally friendly monitoring sensor that does not require collection after installation.

This paper describes an eye-recognizable stimuli-responsive structural-color hydrogel chemical sensor microarray having independent functional structures. Single unit of this microarrayed sensor is separated into two functional parts: a stimuli-responsive part and a structural-color part, enabling visible color sensing for various types of target molecules. In order to demonstrate our concept, we fabricated ethanol and Ag+ ions responsive microarrayed sensors with l00-m-scale units and observed their color change in response to these chemical targets. We believe that our sensor could be applied to continuous environmental monitoring such as water quality, and widen the range of materials for stimuli responsive structural color hydrogel sensors.

This paper describes a tube-shaped in vitro intestinal gut model achieving both isotropic medium supply and stable co-culture with bacteria. Our tube-shaped device consists of a collagen/Matrigel tube as a scaffold for intestinal cells and glass/silicone tubes at both ends for perfusion. We confirmed intestinal cells (Caco-2) can be maintained in the luminal part with nutrient-free buffer flow mimicking bacterial suspensions and demonstrated the co-culture of Escherichia-coli (E. coli) in the Caco-2 cultured tube-shaped device. We believe this device provides ple but stable co-culture model with intestinal cells and bacteria and contributes to medical field research relating intestinal bacteria.

This paper reports ultrasound-triggered adeno-associated-virus (AAV) release from alginate hydrogel microbeads loaded into a gelatin hydrogel carrier to promote the transfection of cells. As a AAV carrier, caldium alginate hydrogel microbeads were centrifugally fabricated by ejecting a mixed pre-gel solution composed of sodium alginate, AAV and tungsten particles to CaCl2 solution to form ionically cross-linked instantly. For fixing of the beads, the microbeads were loaded into gelatin hydrogel carriers. The tungsten particles having high acoustic impedance enable the beads to have high sensitivity to ultrasound for improvement of the transfection. Our proposed ultrasound-triggered AAV releasing system would be an effective controlled release system for gene therapy.

This paper describes exosome-encapsulating micro-hydrogels that enable diffusion-driven release of exosomes (Figure 1). The exosome-encapsulating micro-hydrogels were fabricated (i) by micromolding and (ii) by ejecting exosome-containing pre-gel solution with a centrifugal microfluidic device. We confirmed the permeation characteristics of exosomes by using two types of gels, calcium alginate, and barium alginate whose pore sizes are smaller than the exosome size (30-150 nm). We confirmed that ~25% of the encapsulated exosomes were successfully released from the exosome-encapsulating micro-hydrogels for 4 days, indicating that alginate-based micro-hydrogel could be used for therapeutic system capable of release of exosomes.

We propose a simple and quantitative assessment of cardiac maturation by calcium propagation velocity. A microfiber-shaped cardiac tissue enables the uniform orientation of cardiomyocyte along the fiber direction, allowing the easy calculation of propagation velocities by one-way-transmission of signals over a long distance. We evaluated the maturation of our microfiber tissues by electrical stimulation and detected 26% increase in the propagation velocity comparing to the immature tissue. Our system of maturity assessment would contribute to the construction of matured cardiac model as a platform for elucidating the pathology of cardiac diseases and drug effects.

N,N-Dimethylformamide (DMF) is an essential solvent in industries and pharmaceutics. Its market size range was estimated to be 2 billion U.S. dollars in 2022. Monitoring DMF in solution environments in real time is significant because of its toxicity. However, DMF is not a redox-active molecule; therefore, selective monitoring of DMF in solutions, especially in polar aqueous solutions, in real time is extremely difficult. In this paper, we propose a selective DMF sensor using a molybdenum disulfide (MoS2) field-effect transistor (FET). The sensor responds to DMF molecules but not to similar molecules of formamide, N,N-diethylformamide, and N,N-dimethylacetamide. The plausible atomic mechanism is the oxygen substitution sites on MoS2, on which the DMF molecule shows an exceptional orientation. The thin structure of MoS2-FET can be incorporated into a microfluidic chamber, which leads to DMF monitoring in real time by exchanging solutions subsequently. The designed device shows DMF monitoring in NaCl ionic solutions from 1 to 200 μL/mL. This work proposes the concept of selectively monitoring redox-inactive molecules based on the nonideal atomic affinity site on the surface of two-dimensional semiconductors.

We propose a wireless and battery-free soil pH sensor made entirely of degradable materials for soil pH monitoring in outdoor environments. The sensor consists of magnesium (Mg) electric antenna based on inductor-capacitor circuit resonance with hydroxyapatite (Ca10(PO4)6(OH)2, HA) coating, enabling degradation of the sensor in acid soil conditions. In this report, we succeeded in measuring the changes over time of different electromagnetic responses in soils with different soil pH. Furthermore, the electromagnetic response of the sensor was also demonstrated in the outdoor field experiment. We believe that our biodegradable soil pH sensor could apply to low-cost, in situ, and environmentally friendly monitoring of soil pH.

This paper describes a real-time maturity evaluation system of cardiac tissue with a conduction velocity (CV). A microfiber-shaped cardiac tissue enables easy measurement of CVs by the one-way transmission of signals over a long distance. In addition, CVs can be calculated real-time only with a change in fluorescent intensity, thanks to a visualization of electrical conduction by GCaMP. We measured CVs over 6 days to assess the maturation of the same cardiac tissue in real-time. Our system of maturity evaluation would contribute to the development of a matured cardiac model for elucidating the pathology of cardiac diseases and drug effects.

This paper describes a live-cell imaging system for spatiotemporal analysis of endothelial cellular response to complex mechanical stress in an extracellular matrix (ECM)-based branched in vitro vascular model. The branched in vitro vascular model with ECM scaffolds was fabricated by a sacrificial template-based method. The dimensions and mechanical stresses of the branched area were designed by finite element analysis. Endothelial cells were cultured under shear stress only or shear stress and cyclic stretch stress, and cell orientation was analyzed spatiotemporally at the single-cell and tissue scales.Clinical Relevance - Our results indicate that endothelial cells in vessels in vivo have areas that are strongly and weakly affected by mechanical stress, with a systematic response of cell polarity. In addition, our system would contribute to an effective approach to reproduce the pathogenesis of cardiovascular disease in vitro and elucidate its processes.

Deformation of lithium batteries is known as a hazardous problem possibly leading to a fire or fuming, while deformation sensors are not attached to the batteries. The deformation comes from complex phenomena inside the batteries, resulting in difficult deformation estimation. To display the battery deterioration status more easily, a CSDS (colorimetric stress-detectable separator) is presented that is a separator sensor made of a structural color polymer, enabling to display of the mechanical stress with colors. The structural color polymer consists of aligned silica nanoparticles and PEGPEA (Poly (ethylene glycol) phenyl ether acrylate) acrylic polymer, displaying a specific wavelength depending on the particle gaps. To observe the CSDS color, an observation window is opened to an electrode of the battery. The CSDS showed that there are two stages for gas expansion by displaying a color change from green (≈540 nm) to red (≈580 nm). The separator also displayed blue near the edge of the observation hole, resulting from growing crystals. Those results showed that the separator sensor will contribute to an improvement in battery safety by an easy check from outside the battery packs.

Viscosity is a key physical parameter influencing droplet generation. Herein, the synthesis of hydrogel microparticles from an ultra-high-viscosity pre-gel (UHV-HMPs) solution using a microparticle synthesis device combining centrifugal force with ultrasonic vibration (MSDCU) is reported. The advantage of MSDCU is that it can synthesize closely spherical microparticles from ultra-high-viscosity pre-gel solutions with viscosities exceeding 104 mPa·s in the air/water method. The ultrasonic droplet-shooting module embedded in the MSDCU ejects an ultra-high-viscosity pre-gel solution of sodium alginate through a capillary under ultrasonic vibration to overcome the viscosity limitations of using only centrifugal force. Based on an evaluation of the vibration modes of a multilayer transducer with a capillary at various resonance frequencies, a vibration mode with longitudinal and lateral vibrations of 100 kHz is selected. The combination of ultrasonic vibration at 100 kHz and a centrifugal force of 230g results in the ejection of pre-gel solution with a maximum viscosity of 1.5 × 105 mPa·s. At a viscosity of 1.5 × 104 mPa·s, control of the distance between the capillary and crosslinking solution improves particle circularity, enabling the formation of spherical UHV-HMPs with a diameter of ≈140 µm. With a higher viscosity solution (3.0 × 104 mPa·s), smaller homogeneous satellite particles with a diameter of ≈31 µm are synthesized after filtering.

We present a three-dimensional intestinal hydrogel tube with a crypt-like uneven inner wall fabricated using electrolysis-generated microbubbles. The uneven structure observed in crypt and villus intestinal epithelial tissue in vivo serves as crucial geometry for forming hierarchical tissue consisting of stem cells localized in the crypts and various differentiated cells located in the villi. Our approach utilizes electrically generated microbubbles on a wire mold during the fabrication of the hydrogel tube, resulting in the formation of crypt-like cavities on the inner wall. We fabricated the hydrogel tube with various sizes of crypt-like cavities by changing the voltage-applied time. Caco-2 cells were cultured in the fabricated tubes for over 7 d, and it was observed that they maintained the crypt-like structure. Furthermore, we used immunofluorescence staining to successfully observe the polarity of the intestinal epithelial cells and the unique cell morphology with a specific cell shape and height in response to the crypt-like structure. This specific cell morphology suggests the potential of the tube model to generate hierarchical intestinal tissue. With its highly biomimetic and high-throughput fabrication capabilities, our model will serve as a platform for intestinal models.

This paper proposes a three-layered hydrogel microfiber for improving the stability of the encapsulated three-dimensional (3D) muscle tissue. We formed an intermediate collagen scaffold layer between the outer calcium alginate hydrogel shell and the inner tissue core. An immortalized mouse myoblast cell line, C2C12, was encapsulated in our proposed three-layered (Ca-Alg./collagen/tissue) hydrogel microfibers to examine the stability of the C2C12 tissue. Our proposed microfiber sustained 95% of the original fiber-shaped C2C12 tissue length, whereas the previously reported two-layered fiber could only retain 70% after 11 days in culture, indicating that the proposed three-layered hydrogel microfiber enhanced the stability of the fiber-shaped tissue. We believe our microfiber could be useful to maturate the 3D microfiber-shaped tissues for pathology elucidation, drug efficacy evaluation, and regenerative medicine.

Chirality is an intrinsic property of cells manifested as left-right (LR) asymmetry in terms of cellular morphology and organization, which influences cell behavior, migration, and tissue development. Traditional in vitro methods used to study cell chirality often require complex fabrication methods, limiting their accessibility and reproducibility. Here, we present a novel micropattern tape method that facilitates fabrication of high-quality rectangular micropatterns useful for efficient, high-throughput analysis of cell chirality. Using this method, we characterized chirality of C2C12 myoblasts and MC3T3-E1 osteoblasts, which respectively exhibit clockwise (CW) and counterclockwise (CCW) chirality relative to the long axis of the rectangle. We used the method to analyze how cellular differentiation impacts chirality and observed striking reversal of C2C12 cell chirality upon bone morphogenic protein-2 (BMP2)-induced osteoblastic differentiation. These results demonstrate that our micropattern tape method can effectively detect dynamic change of cell chirality during differentiation.