In-vitro development of highly organized three dimensional (3D) -engineered tissues consisting of multiple types of human cells and extracellular matrix (ECM), which possesses a similar structure and function as natural tissues, is the key challenge for tissue engineering and pharmaceutical assay as modulation of 3D-cell to cell interaction inside the 3D-artificial tissues is one of the significant issues. Nearly all tissue cells in the body reside in the micrometer-sized fibrous meshwork of the ECM. The ECM is typically composed of fibronectin (FN), collagen, and laminin and provides complex biochemical and physical signals. Therefore, control of cellular microenvironment using artificial ECM and growth factors will be important in-vitro technique to control 3D-cell assembly. We have developed a simple and unique "bottom-up" approach, of "hierarchical cell manipulation" and "cell-accumulation" technique, using nanometer-sized Layer-by-Layer films consisting of fibronectin and gelatin (FN-G) as a Nano-ECM. This approach easily provides more than 100-200μm thick 3D tissues with a blood capillary analogous. We have also reported inkjet cell protein printing to fabricate 3D-hepatcite tissue chips with 440 arrays for drug toxicity assay. 3D-cell printing is expected to be the next tissue engineering technology for construction of 3D tissues with precisely controlled structure.
"Cavitas sensors" attached to body cavities such as the contact lens and mouth-guard, which is non-implantable and non-wearable, have attracted attention as self-detachable devices for daily care and medicine. A soft contact lens (SCL) biosensor for in-situ monitoring of tear glucose was fabricated using biocompatible polymers and MEMS techniques. The SCL biosensor showed a good relationship between the output current and glucose concentration in a range of 0.03-5.0 mM. For a physiological application, the change of tear glucose induced by the change of blood sugar level was assessed using the oral glucose tolerance test. The result showed that the tear glucose level increased with the increase in blood sugar level after a delay of 8 min. As another cavitas sensor, a mouth-guard glucose sensor was developed with Pt- and Ag⁄AgCl electrodes on a PETG sheet. The mouth-guard gear is seamlessly integrated with the sensor and a wireless system. In artificial saliva, the glucose sensor is capable of highly sensitive detection over a range of 5-1000μmol⁄L of glucose. Stable and real-time monitoring with the telemetry system has been achieved. The mouth-guard biosensor will be useful for real-time non-invasive saliva glucose monitoring. The novel self-detachable cavitas sensors are expected to improve the quality of life in the near future.
We have developed a fabrication method for flexible and printable thermal sensors based on composites of semi-crystalline acrylate polymers and conductive filler. Under physiological conditions, these devices exhibit large resistance changes close to body temperature, with high repeatability (2000 times). The sensing temperature can be tuned between 25 and 50°C by changing the mixing ratio of acrylate monomers. Furthermore, we demonstrated flexible active matrix thermal sensors that can resolve spatial temperature gradients over a large area. With this flexible ultrasensitive temperature sensor, we measured cyclic temperature changes of 0.1°C in a rat lung during breathing. We have also fabricated a fully flexible wireless fever alarm system, capable of sounding an alarm when a patient's body temperature rises above the normal level. This wireless fever alarm system is comprised of organic complementary circuits, a high sensitivity temperature sensor, and a piezoelectric speaker, powered by flexible solar cells.
Silver nanowires (AgNWs), with at least two dimensions between 1 and 100 nm, have attracted attention as alternative materials for indium tin oxide (ITO) due to their unique conductivity and transparency. We are conducting research on the synthesis of AgNWs, direct patterning of AgNW ink using screen printing procedure, and treatment methods for generating conductivity. In this work, we have achieved a lower sheet resistance of 60 ohms⁄square with high transparency, using photonic curing compared to mechanical pressing. In addition, investigation of bending property showed that a photonic cured electrode endured a bending test far longer than a mechanical pressed electrode. In conclusion, photonic curing is a simple but effective method to make AgNW layer conductive.
Development of silver nanoparticle ink and printing process for printed circuits are presented. We have developed high performance silver nanoparticle ink that can sinter at very low temperatures. Silver nanoparticle ink was optimized for high-resolution inkjet printing system. A fully printed organic thin-film transistor was successfully fabricated using inkjet printing process. An excellent field effect mobility of 0.6 cm2⁄Vs was achieved using the developed silver nanoparticle ink.
Digital recording systems such as image-setters and plate-setters are required to improve the productivity and the image quality. Under these circumstances, a recording technology of multi-beam laser scanning for the drum capstan system was developed using a multi-frequency acousto-optic modulator (AOM) instead of an ultra-fast scanning device for main scan direction. The high quality AOM was developed with phased array type transducers. It achieved a high bandwidth, over 160 MHz more than that of existing systems. With a simultaneous 3-beam generation system design and with interlace scan to avoid an undesired effect by adjacent beams, the fastest recording speed of 5.0 mm⁄s, compared with 2.0-3.0 mm⁄s for existing systems, was achieved. Furthermore, some of the critical parameters of the multi-frequency AOM, such as the treatment of third order intermodulation and photosensitive media, as the design guideline, are discussed.
In recent years, eco-friendly flexographic printing with water-based ink has attracted attention in the field of package printing. FUJIFILM launched a direct laser engraving (DLE) system in the market, which is one of the plate-making methods. It is necessary to control relief shapes, by laser engraving, and surface properties of the plates for higher quality printings. We have studied the laser engraving properties of the plates and plate parameters related to solid density. We inferred that engraving properties are dependent on the laser absorption coefficient, decomposition rate, and calorific value of the polymer. Furthermore, we found that the hardness and surface roughness of the plate are important factors for solid density, as they affect ink uniformity on a print.