Dynamic Na+ Bridges: A 3D Printing Strategy for Hydrogels With High Strength, Low Hysteresis, Strong Adhesion, and Self-Healing

The synergistic optimization of high strength, strong adhesion, high conductivity, and rapid self-healing in hydrogels faces fundamental challenges arising from conflicting mechanisms. Herein, a 3D-printed, ionically conductive interpenetrating double-network hydrogel based on poly (acrylic acid) (PAAc) is developed via the innovative introduction of dynamic Na⁺ bridges. This molecular design enables a unique dual mechanism: the Na⁺ ions not only form reversible ionic bonds that accelerate chain diffusion through bond rupture-recombination but also create an electrostatic shielding effect in the covalent network, which promotes chain extension to improve mechanical strength without sacrificing dynamic properties. Furthermore, Na⁺ ions regulate bound/free water states and reduces energy dissipation during topological rearrangement. These synergistic mechanisms collectively enable the hydrogel to overcome conventional performance trade-offs. The resulting material concurrently enhances mechanical properties (300 kPa tensile, 1.2 MPa compressive strength), adhesion (160 kPa), and self-healing (>90% recovery in 1 h). Biomimetic devices such as an underwater octopus-tentacle gripper, biomimetic crawling suckers, and pressure sensors are fabricated. By integrating hydrogels with 1D convolutional neural network algorithms, a real-time motion behavior recognition system is further developed. The multi-property cooperative design strategy offers a new pathway for the application of intelligent hydrogel materials in soft robotics and flexible electronics.