Developing tough, fatigue-resistant and conductive hydrogels <i>via in situ</i> growth of metal dendrites

Developing hydrogels with high conductivity and toughness <i>via</i> a facile strategy is important yet challenging. Herein, we proposed a new strategy to develop conductive hydrogels by growing metal dendrites. Water-soluble Sn²⁺ ions were soaked into the gel and then converted to Sn dendrites <i>via</i> an electrochemical reaction; the excessive Sn²⁺ ions were finally removed by water dialysis, accompanied by dramatic shrinkage of the gel. Based on <i>in situ</i> transformation from metal ions to dendrites, the method integrated the advantages of ionic conductive fillers, such as LiCl (uniform dispersion), and electrical fillers, such as metal particles (high conductivity). Additionally, the morphology of metal dendrites combined advantages of 1D nanowires (large aspect ratio of the branches) and 2D nanosheets (large specific surface area of the skeleton). The strategy was found to be effective across diverse gel systems (non-ionic, anionic, cationic and zwitterionic). The dense, highly conductive and branched Sn dendrites not only formed a conductive pathway but also interacted with the polymer network to transfer stress and dissipate energy. The resultant gel exhibited a high conductivity of 12.5 S m^-1, fracture energy of 1334.0 J m^-2, and fatigue threshold of 720 J m^-2. Additionally, the gel exhibited excellent sensitivity when used as a wearable strain sensor and bioelectrode. We believe this strategy offers new insights into the development of conductive hydrogels.