Liquid metal/CNTs hydrogel-based transparent strain sensor for wireless health monitoring of aquatic animals

Abstract

Strain sensors are intriguing in advanced electronics and are typically composed of active sensing materials. Good elastic recovery, self-healing, good adhesion, high transparency, and great mechano-response are essential but can be rarely met in one material. Here, we report a wireless strain sensor that exhibits tissue-like mechanical properties (softness), is conformable to soft tissues (heart and tail) and has the lowest limit of detection (0.25 % stretch). After introducing multiwalled carbon nanotubes (CNTs) bridged liquid metal (LM) composites (LM/CNTs), the strain sensor simultaneously achieves excellent transparency and conductivity. This LM/CNTs hydrogel overcomes the limitations of the traditional hydrogel and achieves high conductivity (up to 94 S/m), good stretchability (2,200 %), and a high degree of transparency (93 %), in addition to enough adhesion (20 kPa) and rapid self-healing (20 min). The strain sensor device is composed of intrinsically soft LM/CNTs hydrogel as sensing material, a microcontroller, signal-processing circuits, and Bluetooth transceiver. This device is applied to recording high-quality heartbeat signals and clear in-site observation of cardiac bleeding, which has helped a Chinese sturgeon survive after Caesarean. This approach provides an ideal strategy for protecting and saving endangered animals and broadens the applications of strain sensors.