Hydrogel Sensors\nin an IoT System for Self-Monitoring\nand Remote Monitoring of Massage Pressure

The effectiveness of massage can be enhanced if the pressure\napplied\ncan be monitored continuously. In this study, we described an Internet-of-Things\n(IoT) system based on hydrogel sensors, which allows for self-monitoring\nand remote monitoring of massage pressure. The piezoresistive hydrogel\nwith the compressive energy loss coefficient of 15.7% was developed,\nwhich was attributed to the strong polarization of ammonium phosphate\non water molecules, which was evidenced by nuclear magnetic resonance\n(NMR) transverse relaxation analyses and atomic force microscopy.\nUsing this hydrogel as a pressure-sensing component, we assembled\na wearable sensor capable of quantifying and transmitting massage\npressure with insignificant energy dissipation. By integrating RGB\nLED arrays, the message pressure was indicated by the color states\nof the LEDs. Furthermore, the wearable sensors and LEDs were connected\nto a microcontroller (MCU) chip, an IoT chip, and a cloud server to\nform a sensing-controlled IoT system, enabling visible and remote\nmonitoring of massage pressure.