Mussel-inspired ionic hydrogel for tactile perception: Toward versatility, robustness and sustainability

The ever-growing wearable and implantable medical devices have spawned an urgent demand for integrating tactile sensors and portable power sources into a single device. However, identifying a suitable material that balances electronic and mechanical performance to simultaneously meet the requirements of high biocompatibility, elasticity, conductivity, and versatility for such soft electronic applications remains a challenge. Here, highly conductive and robust ionic hydrogel is synthesized via a mussel-inspired strategy, where cellulose nanofibers (CNFs) and ZIF-8 particles are introduced into poly(acrylic acid-co-2-(methacryloyloxy)ethyl trimethylammonium chloride) (PADH) matrix for achieving mechanical reinforcement. Besides adhesive strengths of 30.26 kPa, strong hydrogen-bonding central to the embedded CNFs/ZIF-8 joint induces densely cross-linked tough panel points and soft-hard layered network structure that provide tensile strength of 110 kPa, elongation at break up to 697 % (increased by ∼2.2 times and ∼1.9 times, respectively) and compressive strength of 984 kPa. Excellent self-healing (89 % within 12 h) and self-adhesion capabilities (adhesion strength of about 30.26 kPa) are also witnessed, which can be attributed to the reversibility of the abundant hydrogen bonds. Meanwhile, the ion-rich tunnels promoted by the migration of IL/Gly/H2O ternary solvent system (EgHTS) not only significantly enhance the ionic conductivity, but also improve temperature tolerance and provide prolonged resistance to dehydration. The dynamical balance of the electric double layers at the CNF-ZIF-PADH interface leads to highly stable and durable hybrid triboelectric-piezoresistive sensors that are capable identifying both the physical characteristic of dynamic objects and static forces while harvesting mechanical energy, thus enabling versatile, robust, temperature-tolerant conductive hydrogels for self-powered soft electronics.