A Flexible and Wearable Strain Sensor from Polypyrrole-Doped Elastomers with Dual Functions in Motion Monitoring and Thermotherapy

Flexible strain sensors are essential components of wearable electronic skins. Here we report a new kind of flexible strain sensor by filling conductive nanowires in elastomers featuring a concentration gradient. The fabrication method involves a fast photo-induced copolymerization of acrylates in the presence of gradient deposited polypyrrole (PPy) nanowires, which is facile and cost-effective in steadily doping PPy into elastomeric films. The combination of delicately selected polyacrylates as the matrix filled with entangled, nano-sized PPy endows the sensor good stretchability, sensitive deformation-electrical signal conversion and high fatigue resistance, which can be used repeatedly without scarifying the sensitivity of electrical signal. Besides, the lower side of the composite films exhibits high light absorption (> 98%) in a wide spectral range (250-2400 nm). Systematic characterizations of the sensors support that the excellent strain sensing and light-heat conversion performances are essentially dependent on the gradient filling of PPy nanowires. Moreover, the applications of this flexible strain sensor for human motion monitoring and wearable thermotherapy are demonstrated, manifesting a promising option for wearable electronics and personalized healthcare.