A wearable, waterproof, and highly sensitive strain sensor based on three-dimensional graphene/carbon black/Ni sponge for wirelessly monitoring human motions

The exploration of wearable strain sensors with new characteristics and functionalities could fuel the rapid development of Internet of Things (IoT) technology for the healthcare industry. Herein, we present a flexible, waterproof, and highly sensitive strain sensor that is fabricated by integrating graphene (G), carbon black (CB), and polydimethylsiloxane (PDMS) into the three-dimensional (3D) framework of commercial Ni sponge via a simple, cost-effective, and scalable drop-coating method. The G/CB/Ni strain sensor demonstrates good flexibility, high sensitivity (gauge factor of 138 at 16% strain), and long-term stability. The G/CB/Ni sensor could not only precisely monitor subtle human motions such as pulse, blinking, and swallowing, but it also shows potential in testing muscle strength. A wireless sensor system that consists of the G/CB/Ni strain sensor, an STM32 controller, a ZigBee module, and a portable power source is assembled, which enables remote transmission of data collected from the sensor to the computer wirelessly. The G/CB/Ni sensor also exhibits excellent waterproofness and can be safely used to monitor human motions under humid conditions and in water. The G/CB/Ni strain sensor featuring flexibility, high sensitivity, and waterproofness has great potential for applications in healthcare management, personal rehabilitation training, and outdoor motion monitoring.