pH‐Based Regulation of Hydrogel Mechanical Properties Through Mussel‐Inspired Chemistry and Processing

Abstract The mechanical holdfast of the mussel, the byssus, is processed at acidic pH yet functions at alkaline pH. Byssi are enriched in Fe 3+ and catechol‐containing proteins, species with chemical interactions that vary widely over the pH range of byssal processing. Currently, the link between pH, Fe 3+ ‐catechol reactions, and mechanical function is poorly understood. Herein, it is described how pH influences the mechanical performance of materials formed by reacting synthetic catechol polymers with Fe 3+ . Processing Fe 3+ ‐catechol polymer materials through a mussel‐mimetic acidic‐to‐alkaline pH change leads to mechanically tough materials based on a covalent network fortified by sacrificial Fe 3+ ‐catechol coordination bonds. These findings offer the first direct evidence of Fe 3+ ‐induced covalent cross‐linking of catechol polymers, reveal additional insight into the pH dependence and mechanical role of Fe 3+ ‐catechol interactions in mussel byssi, and illustrate the wide range of physical properties accessible in synthetic materials through mimicry of mussel‐protein chemistry and processing.