Printed silk-fibroin-based triboelectric nanogenerators for multi-functional wearable sensing

Highlights: • A novel printed silk-fibroin-based triboelectric nanogenerator (PS-TENG) for multi-functional wearable sensing was proposed. • It was firstly demonstrated to distinguish existing states of water molecules due to the newfound property of silk fibroin. • A combination of passive sensing and active sensing within a single device was realized. • An outstanding output of 412 μW/cm² was achieved, and the single-electrode configuration endows it remarkable wearability. • The industrial technology of screen-printing was optimized to fabricate microscale graphite patterns atop soft substrate. -- Abstract: The rapid development of wearable sensing technology exhibits unprecedented opportunities for artificial intelligence by establishing an interactive interface between the physical and the virtual worlds. Energy preservation and multi-functional integration are central for the enhancement of perception and sustainability of wearable electronics. Herein, to address the above two critical challenges, we presented a printed silk-fibroin-based triboelectric nanogenerator (PS-TENG), which can efficiently scavenge the bio-mechanical energy and precisely detect components of environmental humidity and human body motions simultaneously. An industrial mass-fabrication technology, i.e. screen-printing process, was successfully optimized to manufacture graphite-based microscale surface patterns atop polymeric soft substrate to form interdigital electrodes, which was covered by a thin layer of silk fibroin to realize the PS-TENG. The proposed wearable PS-TENG exhibited a remarkable output performance, and the voltage, the current and the power density achieved up to 666 V, 174.6 μA, 412 μW/cm², respectively. Furthermore, this ultra-thin foldable PS-TENG possesses incredible features for multi-functional wearable sensing. With the help of the unique selective absorption property of silk fibroin, it was firstly reported that the existing states of water molecules (i.e., liquid and gaseous) in the air were successfully distinguished. Moreover, as attractive potential applications, it was demonstrated to accurately discriminate the health situation of human body (i.e., respiratory monitoring and joints motion recognizing) based on the capacitive and the triboelectric principles respectively, which is a novel combination of passive sensing and active sensing mechanisms within a single wearable device.