Published papers

Copyright © 2018 The Authors, some rights reserved. Biohybrid robots are attracting attention as promising candidates to enhance robot applicability to studies on biological designs and in vitro construction of biological dynamic systems. Rapid progress in biohybrid robots with skeletal muscle tissues formed on a flexible substrate has enabled various types of locomotion powered by muscle tissue. However, it has been difficult to achieve high levels of both large and long-Term actuations of the skeletal muscle tissues because of their spontaneous shrinkage through the course of the tissue culture. To overcome this limitation, we adapted the concept of biological systems and developed a biohybrid robot actuated by an antagonistic pair of skeletal muscle tissues. Our robot achieved large actuation (∼90° of rotation of a joint) by selective contractions of the skeletal muscle tissues and a long lifetime (∼1 week) by balancing tensions of the antagonistic tissues to prevent the spontaneous shrinkage. As a demonstration, we showed that our biohybrid robots allowed a pick-And-place manipulation of objects. This research may provide a platform to exceed the limitations of design in conventional biohybrid robots and replicate various lifelike movements.

© 2018 by the authors. This paper demonstrates a triple-coaxial flow device to continuously produce a hydrogel microtube using a microfluidic technique. The hydrogel microtube can encapsulate a microbial suspension, while allowing the diffusion of oxygen and nutrients into the microtube and preventing microbes from passing into or out of the microtube. The microtubes also enable the collection of the microbes after task completion without contaminating the environment. In our previous study, we used a double-coaxial flow device to produce the microtubes, but continuous production was a challenge. In the present study, we developed a microfluidic device that fabricates a triple-coaxial flow to enable continuous production of the microtubes. Here, we characterize the production capacity of the microtubes along with their properties and demonstrate bioremediation using microtubes encapsulating a microbial suspension.

© 2018 Wiley Periodicals, Inc. This paper describes three-dimensional (3D) tissue shape control of mouse neural stem cell (mNSC) micro tissues by using closed agarose microchambers for effective differentiation induction of neurons in vitro. Our agarose microchambers, made by micromolding, can be sealed with an agarose sheet to form the mNSC tissues along the shape of microchambers. We constructed lane-shaped mNSC tissues with different width (∼60–210 μm) and thickness (∼25–95 μm) dimensions and induced differentiation to neurons with differentiation medium. We found that in thick tissues (thickness: >60 μm), distribution of differentiated neurons was not uniform, whereas in thin tissues (thickness: ∼30 μm), differentiated neurons were uniformly distributed with high differentiation efficiency. Our system to construct in vitro 3D neural tissues having uniformly distributed neurons at high differentiation ratio, could become an effective tool for drug screening using 3D neural tissues and 3D mNSC tissues under differentiation induction.

© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group and The Robotics Society of Japan. This paper describes a fabrication method and driving property of a biohybrid device with an antagonistic pair of skeletal muscle tissues and a flexible substrate. Since two skeletal muscle tissues are symmetrically arranged with the flexible substrate as the central axis, the flexible substrate deforms according to differences in their tension. In the formation of the antagonistic pair of skeletal muscle tissues, we assembled myoblast-laden hydrogel sheets and cultured them to construct a single skeletal muscle tissue on each side of the flexible substrate. We confirmed that the skeletal muscle tissue on the flexible substrate had the fundamental morphology and function of skeletal muscle. Furthermore, we made the biohybrid device actuate with deformation of the flexible substrate by selective contractions of the skeletal muscle tissues. From the deformation of the flexible substrate, we estimated the contractile force of each skeletal muscle tissue in the biohybrid device using finite element analysis. This biohybrid device, composed of an antagonistic pair of skeletal muscle tissues and a flexible substrate, can potentially be used in biological studies and pharmacokinetic assays involving the antagonistic pair of skeletal muscles.

© 2019 by the authors. We propose a method to print four-dimensional (4D) stimuli-responsive hydrogel structures with internal gaps. Our 4D structures are fabricated by printing an N-isopropylacrylamide-based stimuli-responsive pre-gel solution (NIPAM-based ink) and an acrylamide-based non-responsive pre-gel solution (AAM-based ink) in a supporting viscous liquid (carboxymethyl cellulose solution) and by polymerizing the printed structures using ultraviolet (UV) light irradiation. First, the printed ink position and width were investigated by varying various parameters. The position of the printed ink changed according to physical characteristics of the ink and supporting liquid and printing conditions including the flow rates of the ink and the nozzle diameter, position, and speed. The width of the printed ink was mainly influenced by the ink flow rate and the nozzle speed. Next, we confirmed the polymerization of the printed ink in the supporting viscous liquid, as well as its responsivity to thermal stimulation. The degree of polymerization became smaller, as the interval time was longer after printing. The polymerized ink shrunk or swelled repeatedly according to thermal stimulation. In addition, printing multi-hydrogels was demonstrated by using a nozzle attached to a Y shape connector, and the responsivity of the multi-hydrogels to thermal-stimulation was investigated. The pattern of the multi-hydrogels structure and its responsivity to thermal-stimulation were controlled by the flow ratio of the inks. Finally, various 4D structures including a rounded pattern, a spiral shape pattern, a cross point, and a multi-hydrogel pattern were fabricated, and their deformations in response to the stimuli were demonstrated.

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. Nerve guidance conduits (NGCs) composed of biocompatible polymers have been attracting attention as an alternative for autograft surgery in peripheral nerve regeneration. However, the nerve tissues repaired by NGCs often tend to be inadequate and lead to functional failure because of the lack of cellular supports. This paper presents a chitosan-collagen hydrogel conduit containing cells to induce peripheral nerve regeneration with cellular support. The conduit composed of two coaxial hydrogel layers of chitosan and collagen is simply made by molding and mechanical anchoring attachment with holes made on the hydrogel tube. A chitosan layer strengthens the conduit mechanically, and a collagen layer provides a scaffold for cells supporting the axonal extension. The conduits of different diameters (outer diameter approximately 2–4 mm) are fabricated. The conduit is bioabsorbable with lysozyme, and biocompatible even under bio absorption. In the neuron culture demonstration, the conduit containing Schwann cells induced the extension of the axon of neurons directed to the conduit. Our easily fabricated conduit could help the high-quality regeneration of peripheral nerves and contribute to the nerve repair surgery.

Copyright© (2018) by Chemical and Biological Microsystems Society.All rights reserved. This paper describes a novel method to fabricate three-dimensional (3D) structures composed of a stimuli-responsive hydrogel. Using this method, 3D structures with internal gaps (ex. framed structure, hangout structure etc.) can be printed directly in supporting viscous liquid and polymerized with ultraviolet (UV) irradiation. We confirmed that the fabricated 3D microstructures with internal gaps successfully changed their shapes by external stimuli such as temperature. Our proposed method would be an effective tool for creating hydrogel 3D microstructures with various types of stimuli (optical, pH, molecular, etc.), for applications in soft actuators/robotics, and self-assembly/adaptive systems.

Soft actuators mimicking biological muscles have been built by polymerizing actin and myosin in vitro to construct actomyosin, however, the mechanical strength of the actomyosin was generally not sufficient for practical uses as an actuator. In this study, we proposed an actomyosin-collagen hybrid actuator with high mechanical strength and formability by reconstructing actomyosin biomolecular linear motors inside collagen gel matrix. This actuator can be contracted by adding ATP and returned to its original length by applying an external tensile force, resulting that the actuator could be driven multiple times. This actuator could be expected as an actuator for environment-friendly micro-robots and wearable medical devices.

The fabrication of accentuated gold microstructures is demonstrated by multi-photon photoreduction inside an anionic fluorophore-containing hydrogel. We attempted to facilitate gold-ion photoreduction near the focal point of laser pulses, expecting the donation of electrons by the oxidation of fluorophores in the vicinity of gold ions. The presence of anionic FITCdextran also inhibited the spontaneous reduction in untargeted zones, which is attributed to the coordination of gold ions and the anionic FITC-dextran. Simultaneous facilitation and inhibition are promising for the fabrication of dense metal microstructures in the targeted zone while maintaining the hydrogel's light permeability.

Artificial reconstruction of a highly aligned actomyosin bundle utilizing a laminar-flow microfluidic device enables the fabrication of a bio-actuator mimicking skeletal muscle. At the boundary of two fluid streams involving fibrous myosinⅡ and actin macromolecules respectively, actomyosin bundles are spontaneously assembled and aligned along with the flow direction. We successfully obtained several millimeter-scale actomyosin bundles from the microfluidic devices and also revealed that the actin filament was highly aligned in the bundle, which could enhance the mechanical force produced by contraction. We conceive that our methodology for the assembly of actomyosin bundle would contribute to the development of bio-actuators and furthermore to the understanding of the self-organization mechanism and the mechanical characteristics.

This paper presents a tube-shaped chitosan-collagen hydrogel conduit containing cells for peripheral nerve regeneration. The conduit is simply made by molding, and composed of two layers: A chitosan layer strengthens the conduit mechanically, and a collagen layer provides a scaffold for cells supporting the axonal extension. By using our conduit, peripheral nerves could be regenerated in high quality, because those encapsulated cells release paracrine factors including nerve growth factors (NGF) and supply good environments for nerve tissue reconstruction. We examined the biocompatibility and bioabsorbability of our conduit, and the results represent that our device induced the extension of neurites of neural model cells and was dissolved away in specific terms. We believe this conduit will become a cutting-edge conduit for peripheral nerve surgeries.

We demonstrated the fabrication of gold microstructures inside a PEG-based hydrogel with different charged fluorophores by multi-photon photoreduction. By adding an anionic charged FITC-dextran or a cationic charged Rhodamine110 to the metal ion solution, line width of the fabricated gold microstructures increased compared to that of the structures fabricated in fluorophore-free hydrogel. The photobleaching could enhanced the reduction of gold ions accompanying the oxidation of the fluorophores. Notably, the inhibition of reduction of gold ions at a site other than the focal point was observed with FITC-dextran, which may be attributable to the coordination of gold ions to FITC-dextran.

Many of these microorganisms can change the morphology of their spiral-shaped flagella to control their motility. By mimicking these flagella system, soft spiral-shaped microswimmers for autonomous swimming controlled have been proposed. By patterning the stimuli-responsive hydrogel, the geometry of the microswimmer changes in response to the external stimuli, and thus the swimming velocity is also changed. However, a more detailed analysis of geometry change is essential for the determination of the suitable design and accurate propulsion control. Therefore, we analyzed the deformation behavior in detail. We revealed that the pattern angle is an important parameter for acceleration/deceleration of the microswimmer.

In this research, we propose a method to detect the swell/shrink behavior of stimuli-responsive hydrogel by a strain sensor. The strain sensor is composed of single walled carbon nanotubes (SWCNTs) and a flexible sheet. By integrating the SWCNT strain sensor with a stimuli-responsible hydrogel, the swell/shrink behavior of the hydrogel can be simply sensed as an electrical resistance change of the SWCNT strain sensor. Our approach could contribute to simplify the stimulus detection and could be effective for the integration of high-sensitive chemical sensors with electrical devices.

© 2019 IEEE Soft materials, including elastic polymers and hydrogels, are promising materials for soft robots, implantable devices, and wearable devices owing to their flexibility and biocompatibility. In recent years, the scope of use of such soft materials is expanding further because of their integration with metal micro- and nanostructures, which exhibit attractive optical and electrical properties. In this study, we demonstrate the formation of metal microstructures inside a hydrogel by photoreduction of metal ion by using femtosecond laser. Because the hydrogels have permeability to fluids, metal ions are able to be added by simply immersing the hydrogel into the metal ion solution. Femtosecond laser pulses were focused and scanned in the hydrogel to fabricate metal microstructures [1, 2]. The optical diffraction pattern obtained with the silver grating inside the hydrogel showed spaced diffraction spots, which indicated that a regular, periodic silver grating was formed. Notably, the distance between the diffraction spots changed when the water content in the hydrogel was reduced. The grating period decreased when the hydrogel shrank owing to the loss of water (Fig. 1(a)), but the straight shapes of the line structures were preserved, which demonstrated the optical tunability of the fabricated structure.

© 2019 IEEE. Soft materials, including elastic polymers and hydrogels, are promising materials for soft robots, implantable devices, and wearable devices owing to their flexibility and biocompatibility. In recent years, the scope of use of such soft materials is expanding further because of their integration with metal micro- and nanostructures, which exhibit attractive optical and electrical properties. In this study, we demonstrate the formation of metal microstructures inside a hydrogel by photoreduction of metal ion by using femtosecond laser. Because the hydrogels have permeability to fluids, metal ions are able to be added by simply immersing the hydrogel into the metal ion solution. Femtosecond laser pulses were focused and scanned in the hydrogel to fabricate metal microstructures [1, 2]. The optical diffraction pattern obtained with the silver grating inside the hydrogel showed spaced diffraction spots, which indicated that a regular, periodic silver grating was formed. Notably, the distance between the diffraction spots changed when the water content in the hydrogel was reduced. The grating period decreased when the hydrogel shrank owing to the loss of water (Fig. 1(a)), but the straight shapes of the line structures were preserved, which demonstrated the optical tunability of the fabricated structure.