Flexible, stretchable, breathable and sweatproof all-nanofiber iontronic tactile sensor for continuous and comfortable knee joint motion monitoring

Running improperly for an extended period of time will induce irreversible damage to knee joints, which can bring about excruciating pains to joggers. Wearable sensors for continual knee-monitoring are highly recommended. However, conventional flexible sensors built on airtight substrates are inferior in comfort when wearing for lengthy durations. Herein, a highly flexible and stretchable iontronic tactile sensor is developed on an electrospun thermoplastic polyurethane nanofiber platform. The multilayered, intertwined, nanofiber network housing numerous micro-pores/channels endows the sensor with superior air permeability, sweat inertness, thermal dissipation ability, and biocompatibility, which allows for an extended, comfortable wearing experience. Accrediting the supercapacitive sensing mechanism and porous microstructure, a performance exhibiting a high sensitivity, wide detection range, rapid response, excellent stability and repeatability can be achieved. Pragmatically, a knee-sensor prototype was developed and demonstrated running in real-time and continuously: monitoring a single point of pressure with 3 individual sensor units attached to the rim of the knee and mapping the spatial pressure distribution with an array of sensors covering the whole knee. The health status of the knee could be properly diagnosed, which would be useful for warning of potential knee injuries or to better the form of exercisers.