A reusable, underwater adhesive, self-healing, and conductive hydrogel was developed by the construction of an interpenetrating network structure consisting of a tungstosilicic acid (SiW) cross-linked hydroxypropyl methylcellulose (HPMC) network and a ferric ion cross-linked poly­(dimethylaminoethyl methacrylate) (PDMAEMA) network. The impacts of HPMC, SiW, DMAEMA, and ferric chloride content on adhesion properties were carefully evaluated. The results demonstrated that the 3–2–0.5–60 hydrogel showed the optimal shear adhesion strength. The obtained HPMC/SiW-PDMAEMA/Fe3+ hydrogels exhibited reusable adhesion on the surfaces of various materials such as glass, wood, metals, agate, plastics, ceramics, and rubber. It was noticed that the HPMC/SiW-PDMAEMA/Fe3+ hydrogels also displayed attractive underwater adhesion performance, and they could be adhered to various substrates underwater without any pretreatment or long curing time. In addition, the HPMC/SiW-PDMAEMA/Fe3+ hydrogel showed strain-responsive conductivity and outstanding self-healing performance. Therefore, this work developed a simple method to fabricate reusable, underwater adhesive, conductive, and self-healing hydrogels, which ensure the hydrogel’s broad applicability.

Ultrastretchable, conductive, and autonomous adhesive hydrogels have attracted serious concern due to their wide and promising application in soft electronics, wearable strain sensors, and personal health monitoring. However, traditional hydrogels would lose their properties at subzero temperature, which greatly restricts their applications in a variety of fields. Herein, we fabricated an ionic conductive cellulose hydrogel with ultrastretchable, adhesive, anti-freezing, and self-healing properties. The obtained hydrogel displays ultrastretchability (3280% of tensile strain), anti-freezing property (−32 °C), high conductivity (2.0 S/m at 20 °C, 1.4 S/m at −20 °C), and good self-healing ability. The hydrogel also showed excellent adhesion performance under a broad range of temperatures (9.6 kPa at 20 °C, 5.5 kPa at −20 °C). In addition, the hydrogel-based sensor demonstrated high strain sensitivity and quick responsivity to various human movements. Thus, this work provided a simple pathway to prepare an adhesive, anti-freezing, conductive, and self-healing hydrogel as human motion detection devices.

Conductive hydrogels have shown great potential in the field of flexible strain sensors. However, their application is greatly limited due to the poor antifouling and low mechanical strength. Unfortunately, it is still a challenge to improve these two distinct properties simultaneously. Herein, a hydrogel with high strength, good conductivity, and excellent antifouling and antibacterial properties was prepared through the synergistic effect of physical and chemical cross-linking. First, acrylic acid (AA), acrylamide (AM), and 2-methacryloyloxyethyl phosphorylcholine (MPC) monomers were polymerized in the presence of chitosan chains to form the hydrogel. Then, the prepared hydrogel was immersed in a ferric ion solution to further strengthen the hydrogel through ion coordination. The obtained CS-P­(AM-MPC-AA0.2)-Fe0.1 3+ hydrogel showed outstanding tensile strength (1.03 MPa), excellent stretchability (1075%), good toughness (7.03 MJ/m3), and fatigue resistance. The CS-P­(AM-MPC-AA0.2)-Fe0.1 3+ hydrogel also demonstrated good ion conductivity (0.42 S/m) and excellent antifouling and antibacterial properties. In addition, the strain sensor constructed by the CS-P­(AM-MPC-AA0.2)-Fe0.1 3+ hydrogel showed high sensitivity and good stability. This work presented a facile method to construct a zwitterionic hydrogel with high-strength, conductive, antifouling, and antibacterial properties, which suggested a promising gel platform for flexible wearable sensors.