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

• Published in: Science (American Association for the Advancement of Science) Vol. 328; no. 5975; pp. 216 - 220
• Main Authors: Harrington, Matthew J, Masic, Admir, Holten-Andersen, Niels, Waite, J. Herbert, Fratzl, Peter
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 09-04-2010; The American Association for the Advancement of Science
• Subjects: Abrasion; Abrasion resistance; Amino acids; Animal Structures - chemistry; Animals; Biochemistry; Biological and medical sciences; Biomechanical Phenomena; Chemical Phenomena; Chemistry; Coatings; Coordination chemistry; Crosslinking; Cuticle; Dihydroxyphenylalanine - chemistry; Extensibility; Ferric Compounds - chemistry; Fundamental and applied biological sciences. Psychology; Granular materials; Hardness; Iron; Iron - chemistry; Marine; Materials; Materials research; Materials science; Microcracks; Miscellaneous; Models, Biological; Molecular biophysics; Mollusks; Mytilus - chemistry; Mytilus - physiology; Physical chemistry in biology; Protective coatings; Proteins - chemistry; Proteins - metabolism; Raman scattering; Raman spectroscopy; Repetitive Sequences, Amino Acid; Shells; Spectrum Analysis, Raman; Optical method; Cuticle; Iron; Models; Raman spectrometry; Invertebrata; Mollusca
• ISSN: 0036-8075; 1095-9203
• 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 approximately fivefold harder than the thread core. Threads from several species exhibit granular cuticles containing a protein that is 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 explored byssus cuticle chemistry by means of in situ resonance Raman spectroscopy and demonstrated 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 in which dense cross-linking in the granules provides hardness, whereas the less cross-linked matrix provides extensibility.