Mechanical properties and the laminate structure of Arapaima gigas scales

Mechanical adaptability of the Bouligand-type structure in natural dermal armour

“…This conclusion is further supported by the small amount of diffuse scattering caused by mineral crystals and previous studies indicating a low mineral content 9,10 .…”

“…The outer mineral layer gives the scale hardness and penetration resistance 9,10 , whereas the overlapping of the scales 5 and the corrugated outer surface of the mineral layer 11 allow the scales to bend transferring tensile stress to the inner lower-mineralized lamellae. Through our in situ small-angle X-ray diffraction measurements during mechanical tensile tests of the inner layer of Arapaima fish scales, we found that the unique structural Bouligand-type arrangement of the scale's inner collagen layer has the ability to stretch and reorient the collagen lamellae primarily towards the tensile stress, with some lamellae compressing and reorienting away from the tensile stress.…”

“…Previous studies addressing the mechanical properties of the A. gigas structure have attributed its deformation resistance to the isotropy that the Bouligand structure creates 9 . However, the use of in situ small-angle X-ray scattering simultaneously with tensile testing allows us to track the orientation of the lamellae and their deformation during mechanical testing.…”

“…For Arapaima gigas scales, there are two distinct macro-level regions (Fig. 1c): a hard, highly mineralized outer shell (B0.5 mm thick) and a collagen inner core region (B1 mm thick) 9,10 . The highly mineralized outer shell provides hardness to minimize local plasticity and promote tooth fracture at the point of penetration by the predator; however, it also reduces tensile or compressive stresses during flexure through its corrugated morphology, which limits how much of the scale is under high stress during bending 11 .…”

Characterization Of Multi-layered Fish Scales (<em>Atractosteus spatula</em>) Using Nanoindentation, X-ray CT, FTIR, and SEM

“…Understanding the structure-property relationships for these material systems at the microscale and nanoscale where failure initiates is essential. Currently, experimental techniques such as nanoindentation, X-ray CT, and SEM provide researchers with a way to correlate the mechanical behavior with hierarchical microstructures of these material systems [1][2][3][4][5][6] . However, a well-defined standard procedure for specimen preparation of mineralized biomaterials is not currently available.…”