Tough but self-healing and 3D printable hydrogels for E-skin, E-noses and laser controlled actuators

A versatile hydrogel with extraordinary mechanical strength and self-healing efficiency was developed by integrating physically crosslinked graphene oxide (GO) into a chemically crosslinked polyacrylic acid (PAA) network. The PAA-GO-Ca2+ hydrogel with dual-crosslinked networks exhibited remarkable mechanical properties, such as an outstanding stretchability to 2500% and high toughness (similar to 9.73 MJ m(-3)) along with high stiffness (Young's modulus:similar to 753.667 kPa). The hydrogel also showed a remarkable self-healing capability to maintain similar to 87.47%, 88.02% and 86.93% of its tensile strength, tensile strain, and toughness, respectively, which was attributed to the reversible hydrogen bonding and ionic interactions of Ca2+ with PAA and GO. Reduction was further performed on 3D printed PAA-GO-Ca2+ hydrogels to reduce GO and produce conductive PAA-rGO-Ca2+ hydrogels as wearable biosensors for monitoring different human activities, ammonia detection and laser-driven actuators.