Fig. 5

Multifunctional hydrogel-based wearable strain sensors. A–D Relative resistance changes are measured by the hydrogel sensor fixed onto various regions of the human body including: A forehead, B outer canthus, C side neck, and D chest. These sensors could accurately detect A forehead movements, B eye blinking, C carotid pulsations, and D respiratory activity. E Measured resistance changes of the sensor when the volunteer speaks “self-healing,” “adhesive,” and “conductive.” F Real-time resistance changes of the sensor attached to the knee joint during activities such as walking, running, push-ups, and squatting. G Real-time resistance changes of the sensor attached to the elbow joint during walking, running, push-ups and squatting