This study presents a versatile materials design strategy for functional hydrogels based on electrophoretic adhesion. By applying an electric field, polyelectrolytes embedded within hydrogels are driven toward the interface, where they form a polyion complex (PIC), resulting in strong and reversible adhesion without compromising the intrinsic softness and functionality of the hydrogels. The adhesion strength can be controlled by electric field parameters, and reversible adhesion–detachment is achieved by switching field polarity. Utilizing this mechanism, we developed a three-dimensional construction method using hydrogel beads as building blocks. Under an applied electric field, pasty gel-beads rapidly transform into robust hydrogel structures with tunable mechanical properties governed by size distribution and packing density of gel-beads. This approach also enables efficient repair of damaged hydrogels, restoring mechanical performance close to the original state. Furthermore, the electrophoretic adhesion method allows the integration of conductive polymers with thermoresponsive hydrogels, leading to photothermal actuators that exhibit fast, reversible deformation under near-infrared irradiation. Spatial control of adhesion enables complex motions, such as bending, twisting, and hierarchical deformation. Overall, electrophoretic hydrogel adhesion provides a unified platform for hydrogel structuring, functional integration, and repair, offering broad potential for applications in soft robotics, biomedical devices, and smart materials.

Glassy polymers tend to form crazes that develop into cracks, whereas crystalline polymers undergo yielding, necking, and ductile rupture through plastic flow. The molecular origin of fracture is then considered: single-chain scission is analyzed with the Morse potential and Zhurkov’s kinetic model, and intermolecular slip is treated by molecular orbital analysis of H···H contacts between oriented chains, whose dissociation acts as a precursor to slip-induced rupture. Finally, Griffith’s energy balance, stress intensity factors, and star-shaped crack formation are discussed, and the crack-tip stress field is formulated within two-dimensional elasticity theory.