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 are poorly understood. Herein, we describe 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. Our 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.