Biomimetic Ion‐Orchestrated Hierarchical Armored Hydrogel Coating for Robust and Multifunctional Surface Protection

Abstract Engineering hydrogel coating with hierarchical architecture offers a promising pathway to multifunctional surface protection. However, maintaining structural integrity in such a layered structured system remains a critical challenge due to interfacial mechanical mismatches. Such fragile structures will ultimately compromise their surface antifouling and anticorrosion performance. Inspired by the intriguing skin‐toughening behavior of marine sponges, an ion‐orchestrated structural engineering strategy is presented to modulate the surface microstructure of hydrogel coatings, enabling the rapid assembly of a surface‐confined “armor layer” directly from the hydrogel matrix without compromising its overall structural integrity. Molecular force measurements reveal that diffused metal ions coordinate with embedded tannic acid engineered cellulose nanocrystals (TA/CNC), driving their directional migration toward the hydrogel surface and triggering the in situ self‐assembly as a high‐modulus armor layer (over 700 kPa) that locally reinforces the mechanical robustness of the hydrogel coating. Moreover, this surface‐confined hydrophilic armor layer acts as a multifunctional barrier, suppressing over 97% of oil droplets, protein, and biofluid adhesion, and enhancing surface corrosion resistance by reducing corrosion inhibitor leaching by 84.5% through a unique surface pore‐sealing effect. These findings provide a new paradigm for ion‐driven nanoscale reorganization to tailor surface functionality, paving the way for next‐generation, sustainable protective coatings across diverse applications.