Hydrogel Sensors in an IoT System for Self-Monitoring and Remote Monitoring of Massage Pressure.

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