Silk-based pressure/temperature sensing bimodal ionotronic skin with stimulus discriminability and low temperature workability

Multi-responsive sensing devices have contributed extensively to health monitoring applications. However, the effects of different stimuli often confuse, and thus cause, signal distortion of the sensor response. In addition, many sensing devices cannot work properly at low temperatures. In the present study, a robust regenerated silk fibroin (RSF)-based hydrogel was fabricated with silver nanowires (AgNWs) embedded in the surface. The microstructure of AgNW-embedded RSF surface was introduced using cotton fabric as a template. Afterwards, the hydrogel was immersed in an aqueous calcium chloride solution to introduce Ca(II) ions into the matrix of the RSF hydrogel. Finally, two pieces of the RSF/AgNW/Ca(II) hydrogel were assembled with AgNW layer face-toface to form a dual-responsive ionotronic skin that was sensitive to pressure and temperature. The pressureresponse of the RSF/AgNW/Ca(II) ionotronic skin showed a high sensitivity, short response time, and good durability. In addition, the temperature-response also showed a high sensitivity and good durability from low temperatures (- 30x25e6;C) to high temperatures (50x25e6;C). As a demonstration of its dual responsiveness, 16 pieces of RSF/AgNW/Ca(II) ionotronic skin were combined to make a 4 x 4 array. It demonstrated high sensitivity without interference between the pressure and temperature signals, achieving a significant dual response. A potential application for the simultaneous detection of body temperature and heartbeat was demonstrated by placing the RSF/AgNW/Ca(II) ionotronic skin on the wrist and further indicated the practicality of such an ionotronic skin because it could distinguish between the percussion wave, tidal wave, and diastolic wave in a single waveforms. Therefore, this RSF/AgNW/Ca(II) ionotronic skin that can discriminated between stimuli and work at low temperatures may have great potential in the field of wearable health monitoring equipment.