Shogo Nakata

Wearable, Flexible, and Multifunctional Healthcare Device with an ISFET Chemical Sensor for Simultaneous Sweat pH and Skin Temperature Monitoring

Real-time daily healthcare monitoring may increase the chances of predicting and diagnosing diseases in their early stages which, currently, occurs most frequently during medical check-ups. Next-generation noninvasive healthcare devices, such as flexible multifunctional sensor sheets designed to be worn on skin, are considered to be highly suitable candidates for continuous real-time health monitoring. For healthcare applications, acquiring data on the chemical state of the body, alongside physical characteristics such as body temperature and activity, are extremely important for predicting and identifying potential health conditions. To record these data, in this study, we developed a wearable, flexible sweat chemical sensor sheet for pH measurement, consisting of an ion-sensitive field-effect transistor (ISFET) integrated with a flexible temperature sensor: we intend to use this device as the foundation of a fully integrated, wearable healthcare patch in the future. After characterizing the performance, mechanical flexibility, and stability of the sensor, real-time measurements of sweat pH and skin temperature are successfully conducted through skin contact. This flexible integrated device has the potential to be developed into a chemical sensor for sweat for applications in healthcare and sports.

Human-interactive multi-functional electronic wallpaper integrated with sensors and memory

The internet of things concept has promoted research on human-interactive electronics for wearable devices and robotic applications. One interesting application is wallpaper to monitor a room environment and to act as an electronic message board. To demonstrate the potenital of electronic wallpaper (e-wallpaper), this study prepares a flexible nonvolatile floating gate random access memory (FGRAM) array integrated with a tactile touch sensor array as the message board. Additionally, a temperature sensor array is also laminated to monitor the room temperature. Besides the mechanical flexibility, the fundamental properties of flexible FGRAMs, including the tunneling dielectric thickness, program voltage, and program time dependencies, are characterized. Finally, e-wallpaper is demonstrated as a first proof-of-concept to show a possible platform for future macroscale flexible electronics.

Flexible and high selective pressure sensitive rubber for tactile sensing

This study proposes and demonstrates a multi-layered pillar-like, carbon black (CB)/polydimethylsiloxane (PDMS)-based pressure sensor embedded in silicone rubbers to realize high selectivity of tactile pressure against bending of substrate based on a strain engineering. This device is fabricated by all solution-based process that is eventually applied to all-printing technique. Furthermore, as the first proof-of-concept, real-time tactile sensing is demonstrated for several applications such as wearable devices and robotic artificial skin (e-skin). This finding and demonstration eventually can be applied to the low-cost, high precise tactile sensor that can be conformally covered over any surfaces.

All solution-processed flexible memory integrated with tactile sensor

This study demonstrates a tactile pressure-memorized functional flexible device integrated with a tactile pressure sensor and a resistive random access memory (ReRAM) using all solution-based fabrication process toward low-cost and macroscale flexible electronics. Solution-processed NiO ReRAM shows a stable switching operation with >3 orders-ON/OFF resistance ratio without being affected by bending of the substrate up to 5.6 mm radius. As the first proof-of-concept, carbon black (CB) and polydimethylsiloxane (PDMS)-based tactile pressure sensor is integrated with the ReRAM. The integrated device can successfully memorize tactile information by ReRAM. This demonstration eventually allows us to apply for flexible human-interactive tactile array devices by memorizing tactile or other sensing information.

Flexible integrated chemical and physical sensors toward a wearable healthcare patch

We developed a wearable flexible chemical pH sensor consisted of ion sensitive field effect transistor (ISFET) integrated with a printed flexible physical temperature sensor by developing material systems and optimizing the fabrication process as the first proof-of-concept. A major role of flexible ISFET is to measure pH value of sweat by putting it on a skin. The integrated temperature sensor is used to monitor skin temperature as health condition and to compensate pH value measured by ISFET because the characteristics of ISFET is changed by temperature. By analyzing temperature sensor and ISFET including temperature effect, we could successfully measure real-time pH value and skin temperature. The results show that this flexible integrated device has a high potential to be wearable chemical sensing from sweat in addition to physical health conditions.