Biodegradable, self-powered E-skin for contactless respiratory and epidermal humidity monitoring

Humidity monitoring is vital for respiratory health assessment, yet conventional sensors lack flexibility, back-end power supply, and environmental friendliness, demanding flexible, self-powered, and biodegradable devices. Here, we developed a flexible, fully biodegradable self-powered electronic skin (E-skin) that seamlessly integrates micro-supercapacitors (MSCs) and a humidity sensor. Highly hygroscopic agarose (AG) was selected as both the substrate and gel electrolyte, with Ti₃C₂T_x MXene nanosheet-based interdigital electrode arrays patterned on its surface via in-situ fabrication. No metal interconnects or polymer binders were introduced during the whole fabrication process. The MSCs based on AG/sweat gel electrolyte exhibited high area capacitance (15.6 mF·cm^-2), long-term cycling stability (up to 10,000 cycles), and desired biodegradable properties. Due to the strong interaction between AG and MXene with water molecules by abundant hydrophilic groups such as hydroxyl, the humidity sensor has high sensitivity and a good linear relationship within the range of 11%-97% relative humidity. The integrated E-skin system enables real-time monitoring of human breathing patterns (including the mouth and nose), as well as the humidity levels of non-contact finger touch and skin. This work paves the way for sustainable, self-sufficient wearable electronics in personalized respiratory monitoring.