ABSTRACT
Stretchable, self‐healing, and breathable skin‐biomimetic‐sensing iontronics play an important role in human physiological signal monitoring and human–computer interaction. However, previous studies have focused on the mimicking of skin tactile sensing (pressure, strain, and temperature), and the development of more functionalities is necessary. To this end, a superior humidity‐sensitive ionic skin is developed based on a self‐healing, stretchable, breathable, and biocompatible polyvinyl alcohol–cellulose nanofibers organohydrogel film, showing a pronounced thickness‐dependent humidity‐sensing performance. The as‐prepared 62.47‐μm‐thick organohydrogel film exhibits a high response (25,000%) to 98% RH, excellent repeatability, and long‐term stability (120 days). Moreover, this ionic skin has excellent resistance to large mechanical deformation and damage, and the worn‐out material can still retain its humidity‐sensing capabilities after self‐repair. Humidity‐sensing mechanism studies show that the induced response is mainly related to the increase of proton mobility and interfacial charge transport efficiency after water adsorption. The superior humidity responsiveness is attributed to the reduced thickness and the increased specific surface area of the organohydrogel film, allowing real‐time recording of physiological signals. Notably, by combining with a self‐designed printed circuit board, a continuous and wireless respiration monitoring system is developed, presenting its great potential in wearable and biomedical electronics.
ABSTRACT
The traditional human-machine interaction mode of communicating solely with pressure sensors needs modification, especially at a time when COVID-19 is circulating globally. Here, a transparent, stretchable, resilient, and high-performance hydrogel fiber-based bimodal sensor is fabricated by using a polyacrylamide-alginate double network hydrogel, which features high sensitivity (3.17% cm-1), wide working range (18 cm), fast response/recovery speeds (90/90 ms) and good stability in proximity sensing, and impressive pressure sensing performance, including high sensitivity (0.91 kPa-1), short response/recovery time (40/40 ms), low detection limit (63 Pa) and good linearity. Moreover, the response switch between proximity/pressure modes is measured and non-interfering dual-mode detection is achieved. Notably, the stretchable bimodal sensor is capable of working under 100% tensile strain without degrading the sensing performance. Specifically, the proximity sensor shows good immunity to the strain, while the pressure sensitivity is even promoted. Furthermore, the sensor is tough enough to work normally after punctures from a knife and strikes from a wrench. Notably, the sensor can be used for gesture recognition and subtle pressure detection, such as small water droplets (10 mg), wrist pulse, etc. A 3 × 3 array is further shown for accurate spatial sensing and location identification, verifying the feasibility of its practical application.