Highly synergistic, electromechanical and mechanochromic dual-sensing ionic skin with multiple monitoring, antibacterial, self-healing, and anti-freezing functions

Bionic ionic skin, having the ionic transduction and chromotropic traits of chameleons, along with multiple sensing, antibacterial, self-healing, and anti-freezing functions, is of great importance in a wide range of applications, such as flexible iontronics, health monitoring systems, and smart wearable devices. Although such advanced intelligence universally exists in natural organisms, these characteristics are rarely achieved in artificial materials simultaneously. By mimicking biological skin, here, a novel electromechanical and mechanochromic dual-sensing ionic skin (DSI-skin) with these superior functions is presented for visually monitoring human motions and expiration. The DSI-skin is mainly generated by the introduction of highly-substituted hydroxypropyl cellulose (H-HPC) forming liquid-crystal structures into a multifunctional ionic hydrogel (MFIH) containing Al3+ ions with ionic conduction. The resulting DSI-skin is the first to realize simultaneously sensitive dual-mode sensing of strain (gauge factor: 4.90; response time: 363 ms; mechanochromic sensitivity: 2.14 nm per %), pressure (sensitivity: 3.14 kPa(-1); response time: 631 ms; mechanochromic sensitivity: 8.02 nm kPa(-1)), and humidity (fast response: 0.5 s; wide range: 30-90% RH) via the change of structure color and resistance. More importantly, owing to the highly synergistic effect of Al3+ ions and H-HPC, the DSI-skin is simultaneously integrated with handy color tuning (426-641 nm), outstanding antibacterial (log reduction > 3.43), excellent self-healing (85.0% efficiency), and anti-freezing (-15 degrees C) functions for the first time. These utility functions prolong the service life of the materials and expand their applications in many fields. Interestingly, the DSI-skin is also created with Zn2+ ions. Thus, this investigation provides insights into the design and fabrication of high-performance biomimetic materials.