Self-Healing, Wet-Adhesion silk fibroin conductive hydrogel as a wearable strain sensor for underwater applications

Wearable strain sensors based on conductive hydrogels have attracted much attention due to their great application potential in fields such as human motion and health monitoring. Under the guidance of application, the design of conductive hydrogels with multiple functions has been developed. However, due to the weakening or elimination of some properties of hydrogels by water molecules, the design of wearable sensors suitable for use in wet or underwater environments and with biosafety is still a challenge. In this paper, the conductive polymer polypyrrole (PPy) combined with silk fibroin (SF) and tannic acid (TA) were introduced into the same gel network by in situ polymerization, and the SF/TA@PPy conductive hydrogel was successfully constructed. The hydrogel has stretchability, skin compliance, antibacterial and biocompatibility properties. In air or underwater, SF/TA@PPy can perform self-healing of mechanical properties, electrical properties, and sensing properties without external stimulation. At the same time, the SF/TA@PPy showed excellent wet adhesion to various materials. It has a wide working range, high strain sensitivity and fast resistance response. It still has stable electrical performance after multiple stretching cycles. As a wearable strain sensor, the SF/TA@PPy can directly adhere to the surface of the human body without the aid of external objects. In addition, it can quickly perceive large strain body movements such as finger joints, wrist joints, elbow joints and knee joints. Changes in small-strain physiological signals such as smile, frown, cough and respiration can also be accurately captured. Body motion detection can be carried out not only in air but also in water. Based on stable electrical properties, SF/TA@PPy can achieve effective underwater information transmission by controlling body movement changes to express the Morse code.