Tannic acid-iron dual-catalyst-induced polyacrylamide/sericin hydrogel for strain and pressure sensing

Abstract

With technological advances, demand for flexible hydrogel wearable devices is growing rapidly. However, conventional sensors often struggle to adhere securely to human skin, limiting signal acquisition capabilities-a challenge that demands urgent resolution. This study employs a tannic acid (TA)/ferric chloride (FeCl₃) redox system as a catalyst for rapid polymerisation, yielding a robust, highly adhesive sericin (SS)/polyacrylamide (PAM) hydrogel sensor. The interactions between TA, FeCl₃, and ammonium persulphate (APS) sustain a dynamic redox cycle between Fe³⁺ and Fe²⁺, enabling rapid hydrogel formation. The developed hydrogel exhibits outstanding self-adhesion (191.6 kPa adhesion on pig skin), mechanical strength (0.95 MPa), toughness (2.58 MJ/m³), and compressive strength (2.74 MPa). Furthermore, the incorporation of FeCl₃ endows the hydrogel with an ideal ionic conductivity (4.8 mS/cm). This hydrogel combines comfort, rapid response, and outstanding durability. The resulting hydrogel sensor can measure a wide range of human movements, from large motions such as joint bending, running, and jumping, to subtle actions like speech and heartbeat detection. This approach paves the way for developing a new generation of bionic sensors capable of both strain and pressure sensing.