Overview of birds' beak

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Structure-mechanical properties of birds' beaks

Table 1. Summary of the micro/nano hardness of beaks of three different birds for comparison: woodpecker, toucan > [1] , and hornbill> [2] .


Avian beaks are structural biocomposite materials. Generally, structural biological materials comprise a brittle mineral and ductile protein interacting in a complex structure that is organized in a hierarchical manner [3] [4] [5]. The macrostructure of bird’s beak is mainly composed of bone and a β-keratin sheath covering the bone, which is called the rhamphotheca [6] [7]. A rhamphotheca grows continuously like fingernails and has a multifunctional role including protecting the beak from ambient moisture and carrying a mechanical load with its viscoelasticity during pecking [8] [9]. At the microscale, the rhamphotheca comprises keratin scales with a diameter of approximately 50 μm with the core part of the beak being a closed-cell trabecular-like bone [10] [11] [12] [13]. At the nanoscale level, keratin scales comprise β–keratin filaments and have a small gap between them. For the multiscale mechanical properties, the Young’s modulus of the rhamphotheca was reported as ~1 GPa for toucans and hornbills with its anisotropy depending on the geometry of the keratin scales. Under compression, the stress plateau occurs at 0.3 MPa for the toucan beak and at 2 MPa for the hornbill beak. At the microscale, the reported value of microhardness for the rhamphotheca was ~200 MPa for the toucan, hornbill, and European starling [14]. Contrary to the rhamphotheca layer, the core part of the beak (considered to be bone) had a wide range of microhardness values with respect to the species; 0.27 GPa for toucan beak and 0.39 GPa for hornbill beaks. Seki et al. also reported the nanohardness of the toucan beaks were 0.5 GPa and 0.55 GPa for the rhamphotheca and the foam trabeculae, respectively. The nanohardness of the hornbill beaks were 0.85 GPa and 0.94 GPa for the rhamphotheca and the trabeculae, respectively (Table 1).

References

  1. Y. Seki, S. G. Bodde, and M. A. Meyers, "Toucan and hornbill beaks: A comparative study," Acta Biomaterialia, vol. 6, pp. 331-343, 2010.
  2. Y. Seki, S. G. Bodde, and M. A. Meyers, "Toucan and hornbill beaks: A comparative study," Acta Biomaterialia, vol. 6, pp. 331-343, 2010.
  3. M. A. Meyers, A. Y. M. Lin, Y. Seki, P. Y. Chen, B. K. Kad, and S. Bodde, "Structural biological composites: an overview," Journal of the Minerals, Metals and Materials Society, vol. 58, pp. 35-41, 2006.
  4. C. Sanchez, H. Arribart, and M. M. G. Guille, "Biomimetism and bioinspiration as tools for the design of innovative materials and systems," Nature Materials, vol. 4, pp. 277-288, 2005.
  5. F. Xia and L. Jiang, "Bio Inspired, Smart, Multiscale Interfacial Materials," Advanced Materials, vol. 20, pp. 2842-2858, 2008.
  6. R. H. C. Bonser, "The mechanical properties of feather keratin," Journal of Zoology, vol. 239, pp. 477-484, 1996
  7. R. B. Shames, L. W. Knapp, W. E. Carver, L. D. Washington, and R. H. Sawyer, "Keratinization of the outer surface of the avian scutate scale: Interrelationship of alpha and beta keratin filaments in a cornifying tissue," Cell and Tissue Research, vol. 257, pp. 85-92, 1989.
  8. P. R. Stettenheim, "The integumentary morphology of modern birds—An overview," American Zoologist, vol. 40, pp. 461-477, 2000.
  9. B. W. Ritchie, G. J. Hsarrison, and L. R. Harrison, "Avian medicine: Principles and application; Abridged edition," 1997.
  10. Y. Seki, M. Mackey, and M. A. Meyers, "Structure and micro-computed tomography-based finite element modeling of toucan beak," Journal of the Mechanical Behavior of Biomedical Materials, 2011.
  11. Y. Seki, S. G. Bodde, and M. A. Meyers, "Toucan and hornbill beaks: A comparative study," Acta Biomaterialia, vol. 6, pp. 331-343, 2010.
  12. R. Fecchio, Y. Seki, S. Bodde, M. Gomes, J. Kolososki, J. Rossi Jr, et al., "Mechanical behavior of prosthesis in Toucan beak (Ramphastos toco)," Materials Science and Engineering: C, vol. 30, pp. 460-464, 2010.
  13. Y. Seki, M. S. Schneider, and M. A. Meyers, "Structure and mechanical behavior of a toucan beak," Acta Materialia, vol. 53, pp. 5281-5296, 2005.
  14. R. H. C. Bonser and M. S. Witter, "Indentation hardness of the bill keratin of the European starling," Condor, pp. 736-738, 1993.
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