Liquid metal composites for wearable healthcare sensors

Wearable healthcare sensors can convert various physical signals, physiological signals, and electrophysiological activities of the human body into quantifiable resistive or capacitive changes for real-time health monitoring. Gallium (Ga)-based liquid metal (LM) has become an ideal candidate for wearable healthcare sensors due to its excellent physical and chemical properties, such as high stretchability, high electrical conductivity, self-healing and thermal conductivity, and good biocompatibility. However, the high surface tension of LM makes it difficult to be processed. After LM is modified, the LM surface tension is reduced to be able to form LM composites by tightly bonding with the elastomer matrix, and the LM composites exhibit enhanced electromechanical, thermal, and magnetic properties, among others. Here, we review the fabrication methods of LM composites; we describe in detail the composite forms of LM composites and recent advances in tensile, thermal and electrical conductivity, high dielectric constant and biocompatibility. Sensor devices (e.g., piezoelectric sensors, friction electric sensors, strain sensors, and magnetic sensors) of LM composites for wearable healthcare monitoring are summarized. Finally, challenges and opportunities of LM composites in the neighborhood of wearable healthcare sensors are also discussed.

Graphical abstract