Low-water-content polyelectrolyte hydrogels inspired by human epidermal stratum corneum

Hydrogels typically contain large amounts of water (>80 wt %) and suffer from limitations inherent to high water content, including rapid dehydration under ambient conditions and limited mechanical properties. Herein, inspired by the low water content and stable performance of human epidermis, we report a low-water-content polyelectrolyte hydrogel (i.e., L-hydrogel) that mimics the composition of the human epidermal stratum corneum by employing an integrated hydrophobic/hydrophilic network design. The low water content of L-hydrogels (<12 wt %) leads to superior self-healing capability with a healing efficiency of ∼100%, strength and modulus approaching ∼1 MPa, skin-like fracture toughness (3,390 J/m²), and strong natural adhesions (∼120–1,300 N/m) to both wet and dry surfaces. L-hydrogels also possess stable water content and mechanical properties over time under ambient conditions, enabling long-lasting stable functionality for various types of triboelectric nanogenerators and ionic skins. L-hydrogels hold promise for long-term practical applications in soft ionotronics under ambient conditions.