Published papers

We propose an elastomeric microrobot actuated by ATP-driven biological traction of actomyosin. Our robot is composed of a PDMS thin film part as a body and an actomyosin-embedded collagen hydrogel part as a linear motor. The actomyosin drives the hydrogel linear motor by the hydrolysis of ATP. This actomyosin linear motor could repeatably contract by adding ATP and stretching similar to the driving mechanism of our body. By combining the linear motor part and PDMS actuator part, we succeeded in driving the whole device by the traction force of actomyosin. The traction force generated by the linear motor was estimated from the deformation of the PDMS body. We believe that our device would be a new approach to apply biological motor for micro actuators.

This paper proposes a cell-encapsulated core-shell radiopaque hydrogel microfiber for in vivo cell therapy. The microfiber is composed of barium alginate gel containing zirconia particles in the shell and collagen gel encapsulating mesenchymal stem cells in the core. We confirmed that the cells in the fiber secrete paracrine factors to the outside of the fiber. Moreover, we demonstrated the improvement of the renal function of the rats by delivering the fiber into renal arteries. We believe that our fiber would treat incurable diseases including tissue degeneration.

We propose a device to apply localized electrical stimulation to control cardiac conduction in in vitro cardiac tissue. Our system can initiate the generation of electrical impulses at any location by applying local electrical stimulation to the desired point of the microfiber-shaped cardiac tissue. Our system generated a strong and intense electric field between the electrodes in FEM analysis, indicating only the cardiac tissue between the electrodes was electrically stimulated. We could observe the cardiac conduction optically by visualizing the timing and location of impulses with calcium imaging at any location and time on the tissue. The system enables accurate analysis of cardiac potential and conduction velocity of the heart model, and could contribute to the elucidation of pathological dynamics such as arrhythmia, whose mechanism of occurrence still remains unknown.

We reproduce chemical reactions of blood vessels by a flexibly deformable collagen tube device. The device is composed of an unfixed collagen hydrogel tube, enabling the reproduction of both macro and micro scale deformation of the vessel tissue. In addition, the device is easily perfused because the collagen hydrogel tube is directly attached to silicone tubes. We succeeded in demonstrating the chemical deformation of vessel tissue and endothelial cells by inflammatory mediators. Moreover, the drug testing was presented by anti-inflammatory chemicals. We believe that our flexible culturing device could help the construction of functional blood vessels reproducing in vivo chemical reactions in high similarity, and contribute to biomedical researches and pharmacokinetic testing.

Crypts-like structures are indispensable to fabricating an artificial intestinal tissue reproducing the arrangement of cell types in vivo. This paper presents fabrication of an artificial intestinal tube with an uneven inner wall created by electrolysis-triggered microbubbles. During the fabrication process of a scaffold, microbubbles were generated on a tungsten electrode to form cavities on the inner surface of the collagen hydrogel tube. The method can fabricate numerous crypt-like structures in the order of a hundred micro-meter quickly. We believe that our device will be a platform for investigating complex intestinal diseases due to its high biomimetic properties.

This work reports localized in vivo gene transfer by biodegradation of the adeno-associated virus-encapsulating alginate microspheres (AAV-AMs) loaded in collagen gel carriers. AAV-AMs are centrifugally synthesized by ejecting a mixed pre-gel solution of alginate and AAV to CaCl2 solution to form an ionically cross-linked hydrogel microsphere immediately. The AAV-AMs are able to preserve the AAV without diffusing out even after spreading them on the cells, and the AAV is released and transfected by the degradation of the alginate microsphere. In addition, AAV-AMs can be stored by cryopreservation until use. By implanting this highly convenient AAV-encapsulated hydrogel, AAV-AMs can be loaded into collagen gel carriers to fix the position of the implanted AAV-AMs and achieve localized gene transfer in vivo. In vivo experiments show that the AAV-AMs loaded in collagen gel carriers are demonstrated to release the encapsulated AAV for gene transfer in the buttocks muscles of mice. While conventional injections caused gene transfer to the entire surrounding tissue, the biodegradation of AAV-AMs shows that gene transfer is achieved locally to the muscles. This means that the proposed AAV-loaded system is shown to be a superior method for selective gene transfer.

We propose an in vitro model to mimic the hollow structure of biological tissues (e.g. heart or stomach) using hollow core-shell collagen microgel beads. By using collagen hydrogel as the shell of the microbeads, cells encapsulated inside of the collagen shell can proliferate and form a tissue structure with a hollow center. In this paper, as a first step toward engineered hollow structure tissue formation, we report a fabrication method for core-shell (hollow) alginate microgel beads by a simple droplet-dipping method using a two-layer coaxial nozzle device. To apply collagen hydrogel to this droplet-dipping method, we applied alginate cross-linking network as a template for creating collagen microgel beads and dissolved the alginate network after the collagen hydrogel was stabilized. By combining these techniques, we believe that hollow collagen microgel beads encapsulating cells can easily and massively be produced for reconstructing in vitro hollow organ models.

This paper presents a hydrogel biosensor that can simultaneously sense the co-existence of two substances through mechanical response using aptamer molecular recognition and DNA logic gates. Mechanical response is a preferable property in hydrogel sensors, so we have created a swelling hydrogel biosensor and have also added logical processing abilities to widen the applications of the sensor. We demonstrated the biosensor's ability against two targets, caffeine and theophylline, by measuring the swelling ratio of the hydrogel. We believe that our proposed hydrogel biosensor can be applied to many MEMS and μTAS applications because of its mechanical responsiveness and programmable reactions.

In this paper, we proposed a sensor probe utilizing an electromagnetic metamaterial absorber. This device comprises a tri-layer structure with periodically arranged copper split-ring resonators, a resin layer, and a magnesium layer, forming a complete electromagnetic wave absorber. Magnesium in contact with the soil dissolves in response to soil properties, and wireless measurement of the reflected response due to dissolution enables measurement of soil properties. Simulation and reflection measurement results revealed that this device can absorb 70% of incident electromagnetic waves. Furthermore, we examined the relationship between the reflection spectrum and the polarization direction, as well as the correlation between the time of device placement on soil and the reflection spectrum. The results showed that the device exhibited a low dependency on polarization direction and underwent significant changes in the reflection spectrum with the dissolution of magnesium. Therefore, this device shows a promising potential for a practical application in soil property evaluation.

This paper describes a wireless and battery-free soil pH sensor made entirely of degradable materials. Soil pH monitoring is significant for precision agriculture and environmental conservation because soil health can be estimated by measuring soil pH. Soil pH can be measured by collecting soil samples and analyzing them in a laboratory environment or by inserting an electrode-type sensor into the soil and measuring soil pH on site. However, neither method is suitable for wide-area soil pH sensing for precision agriculture or environmental conservation. Herein, a fully biodegradable wireless pH sensor is presented that can be dispersed to outdoor environment to detect soil acidity. The sensor is operated wirelessly through split-ring resonators (SRRs) that consist of patterned octacalcium phosphate (OCP)-coated magnesium (Mg) on a poly-lactic acid (PLA) sheet. At acidic soil pH, the degradation of each SRR results in a change in the electromagnetic response of the sensor. The operation of the sensor in six different types of acidic soils is demonstrated to distinguish the acidic soil wirelessly. It is expected that the biodegradable sensor can be applied to low-cost, easy-to-use, and environmentally friendly monitoring of soil pH.

This paper describes a two-layered hydrogel microwell array device for single-cell-derived exosome analysis with a cell capture system named 'Cell-capture pitfall'. Our proposed device consists of (i) a first layer of a microwell array with a soluble bottom surface and (ii) a second layer of cell-culture hydrogel array. This device enables efficient single cell capture and long-term culture while isolating exosomes. We achieved a cell capture efficiency exceeding 70% and confirmed that the cells transfer from the upper to the lower wells using the 'Pitfall method'. Furthermore, we maintained viable cell cultures in the device for over 17 days. We believe that this device offers a powerful tool for single-cell exosome analysis and holds promise for advancing our understanding of cancer pathophysiology.

This paper proposes a method to measure the 2-axis force of a droplet collision when it is dropped on the slope surface. To calculate the 2-axis small impact force at the same time, a force plate using the sampling moiré method with a line scan camera and a prism is employed. The sampling moiré method can precisely calculate the pattern's in-of-plane displacement. Moreover, both in-plane and out-of-plane displacements of the pattern are detectable utilizing a prism. Additionally, a line scan camera can capture 10k images in one second with 4096 pixels width, which is sufficient for high precision and high-time resolution displacement measurement.In this report, line&space patterns are attached to a glass plate, which is supported by four springs. The applied 2-axis force is calculated by multiplying the analyzed displacement and spring constant. We fabricated and calibrated the force plate system. It was confirmed that the force resolutions were less than 4 μN for the 2-axis. Finally, droplet collision experiments were conducted under several conditions. The force plate was able to measure impact force during oblique impact with 2-axis.

This paper proposes the control of adeno-associated virus (AAV) release from calcium alginate hydrogel (Ca-Alg.) microbeads with different mesh structures. We found that Ca-Alg. with many cross-linking points have smaller mesh structures than those of normal Ca-Alg. This difference enabled the controlled release of AAV from Ca-Alg. according to the mesh size that can physically trap the AAV particles (~20 nm). As the carriers of AAV, Ca-Alg. microbeads using different mesh structures were fabricated and evaluated the release of AAV. In addition, Janus shaped Ca-Alg. microbeads (Janus microbeads) with different mesh structures between hemispheres were demonstrated to design the precisely controlled AAV release. Controlled release of AAV from Ca-Alg. microbeads with optimized mesh structures could be a biocompatible release system for gene therapy.

This paper describes an arrayed culture device for ring-shaped microscale engineered heart tissues (rEHT) to acquire data on the effect of electrical stimulation for contractile force (CF). Elastic pillars in millimeter-scale culture space were fabricated accurately with a 3D printed mold, enabling rEHT formation with small number of cells (1.0×105 cells). Thus, our device is suited to the acquisition of accurate and large numbers of experimental data. Our device was verified by confirming rEHT's response to electrical stimulation and CF measurement from the pillar deflection. We believe that our device would match to explore the electrical stimulus effect for heart tissue maturation with an AI-driven optimization algorithm.

This paper describes an autonomous exploration system to optimize electrical stimulation parameters for the maturation of in vitro skeletal muscle tissues with Bayesian optimization. We established a cyclic experimental procedures, where (i) C2C12 myoblasts were cultured under multiple electrical stimulus conditions in parallel to promote the maturation, (ii) the cell maturation levels were scored by microscopic image analysis with immunofluorescence staining, and (iii) each maturation score with electrical stimulus condition were then applied to Bayesian optimization to suggest new experimental stimulus conditions for the next cycle of the C2C12 culture to expect higher maturation scores. We performed this experimental cycle repeatedly and derived the trend of electrical stimulus conditions to obtain high maturation scores. The C2C12 myoblasts cultured under the derived condition were also verified by the increase of myogenic gene expression. We believe that our proposed method could reveal optimal application method for tissue maturation, and would contribute to regenerative medicine or other medical technologies using tissue culture.

Advanced sensing technologies such as remote sensing and sensor networks, important for enhancing land use through soil condition monitoring, are facing issues including high machine learning costs, limited measurement point density, and environmental impact. This study introduces a remote sensing method that offers both direct and wide-area sensing of soil properties using a dispersible, biodegradable cuboid-shaped isotropic metamaterial equipped with a water-soluble Mg-based resonance antenna structure. The symmetrical metal patterns ensure isotropic reflectance within the 1.2-3.6-GHz range, enabling robust sensing even when the metamaterial is dispersed randomly on the soil. The degradation of the Mg antenna in the soil presents a significant reflection reduction from 80% to 20% at a 2.4-GHz resonant frequency on the soil, promoting the feasibility of combination with a simple wireless measurement system. Integration with functional coatings that dissolve in response to specific soil substances such as pH-sensitive hydroxyapatite leads to the development of biodegradable soil remote monitoring sensors, offering precise, sustainable land management.

A wireless soil pH sensor is proposed using a sheet-type perfect absorber metamaterial. The sensor utilizes a high-impedance surface metamaterial, which functions as a perfect absorber at the resonant frequency. This sensor has a uniform water-soluble Mg film at the bottom coated with hydroxyapatite that degrades depending on the pH, and a periodic square split ring resonator metamaterial structure made on top of a lossy dielectric plate. The sensor detects the dissolution of the metamaterial due to soil pH conditions through the electromagnetic wave reflection response at GHz frequency. Because of the perfect absorbing characteristics, the influence of soil on the metamaterial's electromagnetic response is blocked, allowing for robust measurement regardless of soil type. By coating the Mg with hydroxyapatite, the difference between acidic (pH = 3.0) and neutral soils can be detected by the time difference by a factor of three in the reflectance change from 40% to 75% reflectance change, indicating a transition from absorptive to reflective of the metamaterial's response, at the resonant frequency of 4.12 GHz.

This paper proposes hollow collagen microgel beads capable of encapsulating cells as a model for mimicking the hollow structure of biological tissues. By using collagen as the outer layer of the beads, the encapsulated cells adhere to the inner wall of the collagen scaffold and form a hollow tissue structure. These hollow collagen microgel beads with cells can be continuously fabricated using a co-axial microfluidic device. Furthermore, we confirmed that 96% of the cells remained viable after the bead fabrication process. The hollow collagen microgel beads were then cultured for five days, during which 96% of the encapsulated cells were still alive and had formed a tissue-like structure. We believe that our hollow collagen microgel beads would have high scalability and the resulting tissues could be used for reconstructing artificial hollow organ models in vitro.Clinical Relevance - The proposed hollow collagen microgel beads enable us to construct three-dimensional tissue in the body, which can be used as a model for elucidating diseases and evaluating drug efficacy.

The integration of soft electronic devices with biological systems has garnered increasing attention for applications such as bioinspired soft robotics and wearable health monitors. These devices are designed to interface with biological surfaces or tissues, mimicking the transmission of electrical signals through neural tissues while ensuring high biocompatibility and flexibility. Conductive polymer hydrogels, combining conductive polymers and hydrogels, have emerged as promising materials owing to their flexibility, stretchability, and biocompatibility. In the realization of advanced soft electronic devices, it is key to employ materials with high flexibility and biocompatibility and, moreover, develop techniques for the fabrication of precise and localized conductive structures inside hydrogels. In this study, we demonstrated the spatially selective polymerization of conductive polymers inside a thermoresponsive hydrogel. A poly(N-isopropylacrylamide) (PNIPAM) hydrogel was immersed in a precursor solution of polyaniline (PANI), and polymerization was induced by femtosecond laser pulse irradiation. Conductive polymer microstructures were successfully fabricated inside the hydrogel. Furthermore, using the thermal responsiveness of the PNIPAM hydrogel, we demonstrated that the electrical resistance of the PANI structures changed in response to temperature. The present method provides a strategy for the precise and localized fabrication of conductive structures inside hydrogels, offering an approach to the fabrication of soft electronic devices.

In this paper, we present a modular stimuli-responsive gel sensor that recognizes specific targets using nucleic acid aptamers and expresses the detection by the swelling of the gel. The novelty of our proposed sensing system is that we integrated a modular design to achieve widespread and efficient detection. In addition, the fact that we are using gels that swell possesses the potential for various applications. We present in this paper the efficacy of the gel sensor against histamine and provide an application example for the gel by integrating it into a microfluidic device.