E-Functionalization of Silk-Based Inherent Fiber Structure: Eco-Friendly Two-In-One” Sensors for Flexible Wearable Devices

Eco-friendly flexible wearable sensors with specific e-functions based on natural biomass materials have attracted much attention. Among them, as an ancient natural biological material, silk is degradable and renewable, with a natural fiber structure, and is considered to be one of the best natural fibers with mechanical properties. However, at present, the introduction of synthetic polymer materials such as polydimethylsiloxane and polyacrylamide into natural biomass materials is still not green," and natural materials should be selected to modify the original materials. Tannic acid (TA) is a natural polyphenolic compound, which has a large number of hydroxyl groups and antioxidant properties. In this paper, silk fibroin (SF) is simply modified by ultrasonic treatment with tannic acid and carbon nanotubes (CNTs), and SF is converted into a tannic acid carbon nanotube composite silk fibroin biobased middle layer (TA/CNTs@SF) and then fabricated into strain and pressure sensors. The sensor made of this material has a sensitive response to external bending and compression strain stimuli, which can realize two-in-one" signal detection. When used as a strain sensor, the fatigue resistance is good. It can detect various human movements such as fingers and facial smiles, etc. In terms of pressure detection, it has a wide sensing range of 0 Pa–103 kPa and a response time of less than 50 ms. Its practicability has been demonstrated in the application experiments of Morse codes and pressure alarm devices. The silk-based eco-friendly two-in-one" sensors obtained from modified silk show great potential in replacing traditional synthetic polymer sensors.