pH induced metal ligand cross links inspired by mussel yield self healing polymer networks with near covalent elastic moduli

doi:10.1073/pnas.1015862108

Growing evidence supports a critical role of metal ligand coordination in many attributes of biological materials including adhesion, self assembly, toughness, and hardness without mineralization. Coordination between Fe and catechol ligands has recently been correlated to the hardness and high extensibility of the cuticle mussel byssal threads and proposed to endow self healing properties. Inspired by the pH jump experienced by proteins during maturation of a mussel byssus secretion, we have developed a simple method to control catechol Fe 3+ interpolymer cross linking via pH. The resonance Raman signature of catechol-Fe3+ cross linked polymer gels at high pH was similar to that from native mussel thread cuticle and the gels displayed elastic moduli that approach covalently cross linked gels as well as self healing properties.