Published papers

© 17CBMS-0001. We present a double-layer collagen microtube device for in vitro perfusable multilayered 3D cell culture. Thicknesses of the collagen layers in the microtube can flexibly designed, and heterogeneous types of cells can be co-cultured in each collagen layer or surfaces. Moreover, while our collagen tube is directly attached to silicone tubes, the collagen microtube can be easily connected to an external pump system for perfusion culture. We believe that our device could help easy fabrication of various tissue models mimicking in vivo, especially blood vessel models or vascularized skin models, and contribute to the development of pharmacokinetic testing platforms and regenerative medicine.

© 2020 IEEE. We present an extracellular matrix(ECM)-based microfluidic device that creates a spatial chemical gradient by interstitial flow. Cells located on surfaces of ECM, such as vascular and skin tissues, are influenced by external factors, including interstitial flows, but few methods have been available to recapitulate such conditions. To address this gap, we developed a microfluidic device that can expose cells cultured on the surface of ECM to a continuous concentration gradient created by the interstitial flow. With a 3D printed water-soluble sacrificial mold, we readily fabricated ECM-based microfluidic devices embedding micromixers and a gradient generator. ECM mimicked the permeability of in vivo environments. Our device will serve as a platform to study cellular phenomena occurring on the surface of ECM, such as vascularization and migration of cancer cells.

© The Royal Society of Chemistry 2020. We present an extracellular matrix (ECM)-based stretchable microfluidic system for culturingin vitrothree-dimensional (3D) vascular tissues, which mimicsin vivoblood vessels. Human umbilical vein endothelial cells (HUVECs) can be cultured under perfusion and stretch simultaneously with real-time imaging by our proposed system. Our ECM (transglutaminase (TG) cross-linked gelatin)-based microchannel was fabricated by dissolving water-soluble sacrificial polyvinyl alcohol (PVA) molds printed with a 3D printer. Flows in the microchannel were analyzed under perfusion and stretch. We demonstrated simultaneous perfusion and stretch of TG gelatin-based microchannels culturing HUVECs. We suggest that our TG gelatin-based stretchable microfluidic system proves to be a useful tool for understanding the mechanisms of vascular tissue formation and mechanotransduction.

© 2020 Author(s). We present an extracellular matrix (ECM)-based gradient generator that provides a culture surface with continuous chemical concentration gradients created by interstitial flow. The gelatin-based microchannels harboring gradient generators and in-channel micromixers were rapidly fabricated by sacrificial molding of a 3D-printed water-soluble sacrificial mold. When fluorescent dye solutions were introduced into the channel, the micromixers enhanced mixing of two solutions joined at the junction. Moreover, the concentration gradients generated in the channel diffused to the culture surface of the device through the interstitial space facilitated by the porous nature of the ECM. To check the functionality of the gradient generator for investigating cellular responses to chemical factors, we demonstrated that human umbilical vein endothelial cells cultured on the surface shrunk in response to the concentration gradient of histamine generated by interstitial flow from the microchannel. We believe that our device could be useful for the basic biological study of the cellular response to chemical stimuli and for the in vitro platform in drug testing.

© 2019 IEEE. We present an extracellular matrix (ECM)-based stretchable microfluidic system for in vitro three-dimensional (3D) tissue culture, which mimics the in vivo blood vessels. The target cells (ex. endothelial cells (ECs)) can be cultured with perfusion and stretch simultaneously in our proposed system. Our ECM (collagen)-based microfluidic device was fabricated by dissolving water-soluble sacrificial molds fabricated with 3D printer. We demonstrated perfusion and stretch of collagen microfluidic devices with culturing human umbilical vein endothelial cells (HUVECs), showing that the cultured cells were stretched along the expansion of the collagen microchannel. We believe that our collagen-based microfluidic stretch system could be a useful tool for understanding the mechanisms of vascular tissue formation and mechanotransduction.

© 17CBMS-0001. This paper describes a poly-dimethylsiloxane (PDMS) microfluidic tube integrated with graphene sheets for an inline flow pressure sensor. The PDMS tube was fabricated by molding and a graphene sheet was transferred on the surface of the PDMS tube. Pressure caused by fluid flow inside the tube was monitored by changes in the electric resistance of the transferred graphene. Our pressure sensor could be suitable for precise pressure measurement of small amount of fluid in microfluidic systems including organ-on-a-chip devices.

© 2019 IEEE. This study describes a graphene-based wireless inline pressure sensor that can be easily inserted between an implanted microdevice and a blood vessel for in vivo blood pressure monitoring. Our wireless pressure sensor is simply composed of a graphene sheet (piezo-resistive sensor) attached on a microfluidic elastic tube and a coil wound up to the tube as a transmitter. The applied pressure inside the tube can be monitored wirelessly by an external receiver coil. We fabricated the sensor system applicable to monitoring the range of typical blood pressure, 10-18 kPa, by designing the sensitivity depending on the stiffness and the thickness of the elastic tube, the turn numbers of the coils, and the distance between the coils. Furthermore, we demonstrated to wirelessly measure the blood-pressure-mimicking pulsed inputs with our sensor that was embedded in a biological tissue. We believe that our wireless inline pressure sensor could be an effective tool for monitoring in vivo implanted medical devices such as microfluidic artificial kidneys.

© 2019 IEEE. This paper describes a drug delivery system (DDS) to release Adeno-associated viruses (AAVs) for gene therapy. Our system has two-level hierarchical structures made of different hydrogel materials: (i) Calcium alginate hydrogel microparticles (\sim 100\ \mu \mathrm{m} in diameter) that can properly immobilize AAVs inside and release them for gene transfection triggered by enzymatic degradation, and (ii) a millimeter-scale collagen sheet that encapsulates those alginate microparticles with AAVs for stable fixation to even a tiny and complicated diseased site in our body, such as an inner ear for the treatment of hereditary hearing loss (Figure 1). We fabricated the AAVs-immobilized hydrogel microparticles and evaluated their AAV releasing functions by measured the gene transfection ratio to cultured HeLa cells. In addition, we also demonstrated that the controlled release of AAVs immobilized in the alginate microparticles embedded in the millimeter-scale collagen sheet can be externally triggered from the outside. We envision that our developed composite hydrogel DDS could be an essential and general tool for gene therapy in practical medical scenes, especially in the treatment at complicated internal sites.

© 2017 IEEE. This paper describes fabrication and applications of stimuli-responsive hydrogel microfibers for biochemical sensors and actuators. Our group has developed stimuli-responsive hydrogel microsprings (SR springs) for mugnifying the shrink/swell movements. The SR springs, made of composite hydrogel of p(NIPAM-co-AAc) and calcium alginate, were continuously formed by using a bevel-tip capillary. By stimulating single-layered or patterned SR springs, we achieved to magnify the shrink/swell movements and to control the direction of the movements.

© 2020 IEEE. This paper describes a locally bendable stimuli-responsive hydrogel actuator with axially patterned functional materials fabricated by a valve-controlled microfluidic device. By application of an external stimuli to the complete actuator, it can be locally bended owing to the axial pattern of the responsive and non-responsive material. These materials are axially patterned on a microfiber through the Y-shaped channel coupled with the open/close motion of the valves in the microfluidic device. The microfluidic device can regulate the on/off of the flow by thin membrane pneumatic valves controlled by a computer. The patterning frequency of the two materials in the microfiber could be adjusted by modifying the switching intervals of the solutions. Also, we successfully demonstrated the curvature-change through heating and cooling. We believe that this locally bendable stimuli-responsive hydrogel could contribute to microfiber-shaped soft actuators, biomedical sensors, and self-assembly of complex 3D microstructures.

© 2020 IEEE. This paper describes a multi-color microfluidic reflective display with sub-pixels. Our display is composed of four independent three-dimensional (3D) PDMS microchannels where CMYK (Cyan, Magenta, Yellow, Key plate) ink droplets are spatially positioned as CMYK sub-pixels. By combining CMYK sub-pixel colors, our device displays multiple colors on a single pixel. We evaluated the optical characteristics of each CMYK sub-pixels and confirmed that multi-colors can be displayed by adjusting the combination of sub-pixel colors. We believe that our display could be applied to next-generation wearable displays and sign boards as a low-energy consumption, flexible and full-color reflective display.

© 17CBMS-0001. This paper describes a microfluidic-based multicolor reflective display using dyed water droplets as pixel elements. Our display was composed of a PDMS sheet with a connected pixel-patterned microchannel. Several types of water droplets and air gaps were sequentially introduced in the microchannel by sucking with a syringe pump to display . We evaluated the stability of minimum continuous number of water and air dots to display images correctly. We demonstrated displaying three colored dot-matrix reflective images. We believe that our display could be applicable to energy-less and color-changeable displays for future advertising signage or accessories including bags, shoes, or cloths.

© 2019 IEEE. This paper describes an analytical platform to control endothelial tube formation by patterning cells and extracellular matrix (ECM) within 3D lane-shaped pattern. By using PDMS groove patterns (50-250\ \mu \mathrm{m} in width and height, several millimeters in length), human umbilical vein endothelial cells (HUVECs) were patterned three-dimensionally in collagen gel. The patterned HUVECs spontaneously form endothelial vascular tissues, but their morphologies can be controlled by the dimensions of patterns, cell densities, ECMs, etc. We succeeded in forming vascular tube tissues, and found that a number of branches of the vascular tissues depends on the dimensions of 3D-patterns. We believe that our culture system could be a useful tool for understanding the tube formation behavior of endothelial cells and for creating 3D-shape-controlled vascular tissues as a quantitative model in vitro.

© 2019 IEEE. This paper describes a method to fabricate three-dimensional (3D) microstructures composed of multiple types of stimuli-responsive hydrogels. Using our method, multi-hydrogels 3D microstructures with internal gaps (ex. framed structure, beams structure etc.) can be printed and polymerized in supporting viscous liquid. We fabricated straight-line patterns composed of two types of hydrogels (pNIPAM: stimuli-responsive, and pAM: non-responsive). The printed multi-hydrogel structures were evaluated for the printing accuracy and the stimuli-responsivity to ensure their deformation controllability. Our proposed method would be an effective tool for creating multi-hydrogel 3D microstructures with various types of stimuli (optical, pH, molecular, etc.), for applications in soft actuators/robotics, and self-assembly/adaptive systems.

Tissue engineering is a promising technology for both its possible applications in the fields of regenerative medicine and medical research. One of its challenges is to create an environment which allows the cell cultures to develop correctly. This environment is far from static and normally is modified by the cells themselves. To this end, adaptable systems have to be developed to ensure a successful development of the in-vitro tissue. This research focuses on a system which is able to modify an external electrical stimulus on a culture chamber, during its cultivation. This system, through a variation of the stimulus direction, successfully improved the orientation of the developing myocytes.

Photonic colloidal crystal hydrogels are expected to be a powerful tool for environmental monitoring and healthcare. The photonic colloidal crystal hydrogel reflects visible-light, so the intensity of the stimulus can be converted to visible color. However, these sensors required taking a measured sample from the target environment. To detect a specific substance in a vast environment, exploring and detecting systems are required. Therefore, we proposed ethanol driven micro-robots with photonic colloidal crystal hydrogel. We achieved the color changes of micro-robots response to the external stimuli. Proposed micro-robots propelled over 600 s by the Marangoni effect caused by ethanol diffusion.

We present fluorescent Janus hydrogel microbeads for continuous glucose sensing with pH calibration. The Janus hydrogel microbeads, that consist of fluorescent glucose and pH sensors, were fabricated with a UV-assisted centrifugal microfluidic device. The microbead can calibrate the pH values of its surroundings and enables accurate measurements of glucose within various pH condi-tions. As a proof of concept, we succeeded in obtaining the accurate value of glucose concentration in a body-fluid-like sample solution. We believe that our fluorescent microbeads, with pH calibration capability, could be applied to fully implantable sensors for continuous glucose monitoring.

This paper describes a new approach to fabricate a flexible circuit that has stable electric resistance value against deformation. The flexible circuit is fabricated by depositing metal wiring on a folded flexible origami structure. We confirmed that the resistance value of the metal wiring on the origami structure was stable against stretching and bending compared to that of the wiring formed on a simple elastic flexible sheet. Using this origami structure, we demonstrated a simple wearable device that fits a wrist. We believe that this origami-based flexible device could be a one possible route to robust and stable wearable devices that can be freely and largely expanded.

The mechanical strength of hydrogel microstructures is crucial for obtaining the desired flexibility, robustness, and biocompatibility for various applications such as cell scaffolds and soft microrobots. In this study, we demonstrate the fabrication of microstructures composed of cellulose nanofibers (CNFs) and poly(ethylene glycol) diacrylate (PEGDA) hydrogels by multiphoton polymerization. The stress of the fabricated microstructure during tensile testing increased with an increase in the CNF concentration, indicating that the mechanical strength of the microstructure was enhanced by using CNFs as fillers. Moreover, the swelling ratio of the microstructure increased with increasing CNF concentration in the PEGDA hydrogel. Our results show the potential of the technique for the microfabrication of advanced cell scaffolds and soft microrobots with the desired mechanical strength.

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. Recently, the construction of models for multicellular systems such as tissues has been attracting great interest. These model systems are expected to reproduce a cell communication network and provide insight into complicated functions in living systems./Such network structures have mainly been modelled using a droplet and a vesicle. However, in the droplet and vesicle network, there are difficulties attributed to structural instabilities due to external stimuli and perturbations. Thus, the fabrication of a network composed of a stable component such as hydrogel is desired. In this article, the construction of a stable network composed of honeycomb-shaped microhydrogels is described. We produced the microhydrogel network using a centrifugal microfluidic technique and a photosensitive polymer. In the network, densely packed honeycomb-shaped microhydrogels were observed. Additionally, we successfully controlled the degree of packing of microhydrogels in the network by changing the centrifugal force. We believe that our stable network will contribute to the study of cell communication in multicellular systems.