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Biological Materials Investigations

The microstructure of the teeth of pink sea urchins (
Strongylocentrotus fragilis) at various ocean depths (100 m, 300 m, 700 m, 1100 m) is under investigation. Magnesium (Mg) content of the tooth increases toward the grinding tip at the distal end, which contributes to the increasing hardness at the tip. For individual teeth analyzed at each depth, elemental composition, hardness, and elastic modulus is compared to assess how ocean depth affects material properties of sea urchin teeth. SEM micrographs (above) are of microstructures in pink sea urchin tests (top row) and individual teeth from Aristotle’s lantern (bottom row).


Collaboration with Prof. Lisa Levin, Prof. Jennifer Taylor and Kirk Sato at Scripps Institution of Oceanography

Contact: Mike Frank (mbfrank@ucsd.edu)

Porcupinefish (Diodontids) belong under the umbrella of pufferfish, which are able to inflate roughly three times their original size to thwart predators. The term pufferfish refers to the families Tetraodontidae and Diodontidae. One of the differences between the two families is that Diodontids have spines that are modified scales, while Tetraodontids do not. With regards to spine type, there are two groups of Diodontids: ones with fixed spines and ones with erectable spines that move when the fish puffs up. The genus Chilomycterus contains species that have short, fixed spines, while the other genuses have long, erectable spines. Three porcupinefish species are shown: (a) Chilomycterus schoepfi, (b) Diodon holocanthus, and (c) Dicotylichthus myersi. Their corresponding micro-CT scans are shown in (d-f) beneath the image of the fish. Each group of micro-CT images shows the right lateral, anterior, posterior, and dorsal view of the fish starting from the top left image going clockwise. Scale bars: (d-f) 1cm.



Contact: Frances Su (fysu@eng.ucsd.edu)

The seahorse is covered by bony plates along the entire body. The segments in the tail have four L-shaped bones. Compression of the tail in the transverse direction leads to sliding of the L-shaped segments and buckling of the struts (struts hold the segments to the vertebra).  Large strains of ~60% can be sustained.

Taken from:

  • Porter, M.M., E. Novitskaya, A.B. Castro-Ceseña, M.A. Meyers and J. McKittrick, “Highly deformable bones: Unusual deformation mechanisms of seahorse armor,” Acta Biomaterialia, 9, 6763-6770 (2013).

Contact: Joanna McKittrick (jmckittrick@eng.ucsd.edu)


(a) The boxfish has is covered by hexagonal-shaped bony plates, (b) micro-computed tomography images show the uniformity of the plates and the bilateral symmetry, (c) the plates have triangular teeth that interlock with adjacent plates, (d) the plates have raised reinforcing ridges, helping to resist biting from predators.

Contact: Steven Naleway (snaleway@eng.ucsd.edu)
 

(a) The porcupine is covered with quills, that are lightweight, strong and stiff.  The quill has an outer sheath (cortex) enclosing a porous material - both are made of keratin, (b) compression of quill sections show deformation modes such as cortex buckling, stretching and tearing of the foam walls. The foam remains firmly attached to the cortex, (c) stress-strain curves for the quill and the cortex (foam removed), showing the quill has a greater stiffness, strength and toughness than the cortex, demonstrating the significance of the foam interior.

Adapted from:

  • Yang, W., C. Chao and J. McKittrick, "Axial compression of a hollow cylinder filled with foam: A study of porcupine quills," Acta Biomaterialia, 9, 5297-5304 (2013). DOI: 10.1016/j.actbio.2013.07.004
  • Yang, W. and J. McKittrick, “Separating the influence of the cortex and foam on the mechanical properties of porcupine quills,” Acta Biomaterialia, 9, 9065-9074 (2013).  DOI: 10.1016/j.actbio.2013.07.004

Contact: Joanna McKittrick (jmckittrick@eng.ucsd.edu)

Hierarchical structure of bighorn sheep (Ovis canadensis) horn.  The horns show a spiral fashion with ridges on the surface, which correspond to the seasonal growth spurts.  Horns are composed of elliptical tubules, embedded in a dense laminar structure.  Each lamina has oriented keratin filaments interspersed in a protein-based matrix.  These filaments are two-strand coiled-coil rope polypeptide chains (intermediate filament type I and II) helically wound assemble forming 'superhelical' ropes of 7 nm in diameter.

Taken from:

  • Tombolato, L., E.E. Novitskaya, P.-Y. Chen, F.A. Sheppard, J. McKittrick, "Microstructure, elastic properties and deformation mechanisms of horn keratin," Acta Biomaterialia, 6, 319–330 (2010).

Contact: Joanna McKittrick (jmckittrick@eng.ucsd.edu)


The woodpecker has a pretty amazing impact resistant skull.  It drums up to 12,000 times/day with decelerations of over 1000 g’s, well above the 98 g’s that will cause concussions. One contribution may be the unusual tongue, which is a bone, called the hyoid bone, that wraps around its skull.  We have looked at the tongue to identify the composition and microstructure, to determine the influence it has on the impact resistance of the skull.  Shown here are micro-computed tomography images of the head, showing the high density tongue

Contact: Jerry Jung (jyjung@eng.ucsd.edu)

Antlers must be strong, resist bending and be able to resist fracture.  (a) Hierarchical structure of antler, (b) cross-section showing a dense outer sheath and porous interior, (c) micro-computed tomography images of the longitudinal and cross-sections, (d) the dense bone (cross-section) consists of primary osteons that are irregularly shaped, (e) the collagen fibrils are aligned in the dense bone and composed of (f) nanocrystalline hydroxyapatite minerals, (g) the jagged fracture surface indicates a crack can't travel in a straight line, (h)  toughness as a function of crack length, showing the antler has a high resistance to fracture, compared to human bone.

Taken from: 

  • Chen, P.-Y., A.G. Stokes and J. McKittrick, "Comparison of the structure and mechanical properties of bovine femur bone and antler of the North American elk (Cervus elaphus canadensis)," Acta Biomaterialia, 5, 693-706 (2009). DOI: 10.1016/j.actbio.2008.09.011
  • Launey, M.E., P.-Y. Chen, J. McKittrick and R.O. Ritchie, “Mechanistic aspects of the fracture toughness of elk antler bone,” Acta Biomaterialia, 6 (4), 1505-1514 (2010). DOI: 10.1016/j.actbio.2009.11.026

Contact: Joanna McKittrick (jmckittrick@eng.ucsd.edu)


The armadillo is a mammal found from North to South America. They are covered by bony plates which are hexagonally-shaped in the pectoral and pelvic regions.  The tiles are held together by non-mineralized collagen fibrils, which provide flexibility to the torso.

Adapted from:

  • Chen, I., V. Correa, M.I. Lopez, P.-Y. Chen, J. McKittrick, M.A. Meyers, "Armadillo osteoderm: Mechanical testing and micro-structural examination, Journal of the Mechanical Behavior of Biomedical Materials, 4, 713-722 (2011).

Contact: Joanna McKittrick (jmckittrick@eng.ucsd.edu)



The toucan is a bird that lives in Central and South America. They have a beak that can be over half the body length and therefore must be lightweight and strong enough to gather food.  The beak has a hollow core, surrounded by a highly porous bone and covered by a layer of waterproof keratin.

Adapted from: 

  • Meyers, M.A., Y. Seki, M.S. Schneider, “Structure and mechanical behavior of a toucan beak,”Acta Materialia, 53, 5281-96 (2005).  DOI: 10.1016/j.actamat.2005.04.048
  • Seki, Y., S.G. Bodde, M.A. Meyers, “Toucan and hornbill beaks: A comparative study,” Acta Biomaterialia, 6, 331-343 (2010). DOI: 10.1016/j.actbio.2009.08.026
  • Fecchio, R. S., Y, Seki, S.G. Bodde, M.S. Gomes, J. Kolososki, J.L. Rossi, M.A. Gioso, M.A. Meyers, “Mechanical behavior of prosthesis in Toucan beak (Ramphastos toco),” Materials Science and Engineering C, 30, 460-464 (2010). DOI: 10.1016/j.msec.2010.01.001
  • Seki, Y., M. Mackey, M.A. Meyers, “Structure and micro-computed tomography-based finite element modeling of Toucan beak,” Journal of the Mechanical Behavior of Biomedical Materials, 9, 1-8 (2012). 

Contact: Marc Meyers (mameyers@eng.ucsd.edu)

 

(a) The rachis of a feather (long slender shaft) has solid foam at the dorsal (tip) end, foam and a hollow center in the middle and has struts at the proximal (near body) end. (b) The keratin fibers are in the longitudinal and circumferential direction, which are segmented. The foam has porous walls, further reducing the weight.  The whole feather is lightweight, stiff and strong.

Contact: Tarah Sullivan (tnsulliv@eng.ucsd.edu)

(a) Hierarchical structure of the Arapaima gigas scales. Overlapping scales, graded materials properties through the thickness and Bouligand-type lamella increase toughness. (b) Deformation and toughening modes. Mineralized collagen fibrils re-orientate during loading, leading to lamella rotation.

Adapted from:

  • Zimmermann, E.A., B. Gludovatz, E. Schaible, N.K.N. Dave, W. Yang, M.A. Meyers, and R.O. Ritchie, “Mechanical adaptability of the Bouligand-type structure in natural dermal armor,” Nature Communications, 4, Article 2634 (2013). DOI 10.1038/ncomms3634

Contact: Marc Meyers (mameyers@eng.ucsd.edu)

 

One of the most interesting examples of structural adaptation in nature is the internal structure of avian wing bones. In flying birds, bones need to be strong and stiff enough to withstand forces during takeoff and landing, which necessitates some reinforcement in the bone interior. Wing bones have to resist both bending and torsion loads; they are rarely loaded in pure tension or compression. (A) The structure of a Turkey vulture wing bone, showing the internal struts and ridges. (B) Optical microscopy images of the microstructures of soaring (Turkey vulture), gliding (sea gull), flightless (domestic duck) and flapping (raven) birds.  The duck bone shows higher density. (C) Finite element analysis of the Turkey vulture ulna with struts in the interior. (D) Micro-computed tomographic images of cross-sectional sections along the length of Turkey vulture wing bones.

Contact: Joanna McKittrick (jmckittrick@eng.ucsd.edu)
 
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