Soft wearable devices for deep-tissue sensing

Wearable devices with skin-like mechanical properties enable continuous monitoring of the human body. However, wearable device design has mainly focused on recording superficial signals from the skin thus far, which can only reveal limited information about health and disease. Deep-tissue signals, for example, electrophysiologic, metabolic, circulatory, thermal and mechanical signals, often have stronger correlation with disease and can predict the onset of symptoms. In this Review, we discuss the engineering of soft wearable devices that can sense signals in deep tissues. We highlight electrical, electromagnetic, thermal and mechanical sensing approaches, investigating sensing mechanisms, device designs, fabrication processes and sensing performance, with a focus on penetration depth and temporal and spatial resolutions in the human body. Finally, we discuss remaining challenges in the field and highlight strategies to further improve penetration depth and specificity, accuracy and system-level integration.