Organic composite is exceptionally robust: jumbo squid

1 of 2 Scientist exposing beak of Humboldt squid / The Monterey.. / License

The beaks of jumbo squid have exceptional hardness and stiffness in part thanks to composites of chitin strands cemented in layers by crosslinked proteins and catechols with varying degrees of hydration.

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Strong yet lightweight ceramics and construction materials

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[Collapse all sections] Summary

Jumbo squids produce beaks that are superior to many man-made materials due to their combination of strength, lightness, flexibility, and crack resistance. Squid beaks are composed of strands of chitin (a carbohydrate) cemented together in layers by cross-linked proteins and catechols. Water content imparts flexibility, so a high water content is found at the flexible base of the beak where it attaches to the body. The water content gradually decreases further from the body – the tip of the beak is strong, stiff, and dehydrated. Layering keeps cracks from propagating.

Excerpt

"Dosidicus gigas (jumbo squids) do not use minerals in their powerful mouthparts known as beaks. Their beaks instead consist of a highly sclerotized chitinous composite with incremental hydration from the tip to the base...in contrast to mammalian hard tissues, the beak is devoid of minerals, consisting instead of a composite of proteins and chitin fibers with varying degrees of hydration along the beak structure...As the beak lacks any of the known strengthening entities previously associated with wear-resistant tissues such as biomineralization, metal ion cross-linking, or protein halogenation, it begs a question, namely, what sort of molecular processing can impart such impressive physical properties?" (Miserez et al. 2010:38115)

"Beaks are produced in a wet environment, grow continuously during the lifespan of the animal, and are fabricated with macroscopic biochemical gradients resulting in a wide range of mechanical properties, namely a flexible proximal region attached to the buccal mass and a hard, stiff rostrum at the distal end." (Miserez et al. 2010:38120)

"In addition to the dimeric His-dopa cross-link, trimeric and tetrameric 4MC- His derivative adducts are released from the beak during hydrolysis." (Miserez et al. 2010:38121)

"[C]hitin nanofibrils are assumed to form the initial template, similar to glass fibers or carbon fiber mats in composite processing. Protein 'fillers' and catechols are then secreted through the chitinous preform. Once oxidation of catechols moieties has been triggered (either by autoxidation or enzymatic processes), cross-linking and hardening (sclerotization) ensue...there are at least 3 orders of magnitude difference in the stiffness of chitin/chitosan between the fully hydrated state (where it is present as a porous, water-saturated scaffold) and the dry state." (Miserez et al. 2010:38122)

"Covalent cross-linking is undoubtedly important in the stiffening and hardening of beak...The beak has a lamellar organization, which deflects propagating cracks, redistributes stresses in front of cracks, and necessitates renucleation of cracks in neighboring lamellae. These are energy-dissipating processes that ultimately endow the beak with a high fracture toughness...We propose that the beak is produced by a process reminiscent of the manufacture of fiber-reinforced composites whereby chitin fibers form an initial scaffold subsequently impregnated by a blend of proteins and catechols and cured via catecholic cross-linking." (Miserez et al. 2010:38123)

About the inspiring organism

jumbo squid
Dosidicus gigas (D'Orbigny, 1835 in 1834-1847)
[Jumbo squid]

Some organism data provided by: ITIS: The Integrated Taxonomic Information System
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

Bioinspired products and application ideas

Application Ideas: Strong yet lightweight ceramics and construction materials. Composite materials are the future of materials sciences because they combine the strengths of different substances; jumbo squid beaks represent a remarkable biopolymer composite worthy of modeling.

Industrial Sector(s) interested in this strategy: Manufacturing, construction

Ultra-hard Material - Stronger steel; Body armor

Experts

Materials Department
Frank W. Zok
University of California Santa Barbara

Waite Research Lab
Herbert Waite
Department of Molecular, Cellular and Developmental Biology, University of California Santa Barbara

References

Miserez, A.; Li, Y.; Waite, J. H.; Zok, F. 2007. Jumbo squid beaks: Inspiration for design of robust organic composites. Acta Biomaterialia. 3(1): 139-149.

Messersmith, PB. 2008. Multitasking in Tissues and Materials. Science. 319(5871): 1767-1768.

Miserez A; Rubin D; Waite JH. 2012. Cross-linking chemistry of squid beak. Journal of Biological Chemistry. 285(49): 38115-38124.

Organic composite is exceptionally robust: jumbo squid

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