Iron-Clad Fibers: A Metal-Based Biological Strategy for Hard Flexible Coatings

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Science  04 Mar 2010:
DOI: 10.1126/science.1181044


The extensible byssal threads of marine mussels are shielded from abrasion in wave-swept habitats by an outer cuticle that is largely proteinaceous and ~5-fold harder than the thread core. Threads from several species exhibit granular cuticles containing a protein rich in the catecholic amino acid 3,4-dihydroxyphenylalanine (dopa), as well as inorganic ions, notably Fe3+. Granular cuticles exhibit a remarkable combination of high hardness and high extensibility. We explore byssus cuticle chemistry by in situ resonance Raman spectroscopy and demonstrate that the cuticle is a polymeric scaffold stabilized by catecholato-iron chelate complexes having an unusual clustered distribution. Consistent with byssal cuticle chemistry and mechanics, we present a model where dense cross-linking in the granules provides hardness, whereas the less cross-linked matrix provides extensibility.