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Nanomolecular explanation for the toughness of antler bone
DOI:10.1038/bonekey.2014.53
The nanomolecular mechanisms that confer a high degree of toughness to bone are not well understood. Gupta et al. chose to study antler, a particularly tough bone-type containing mineralized fibrils of collagen, to find out more about its behavior during and after cyclic loading.
Synchrotron X-ray scattering (SAXD) and wide-angle X-ray diffraction (WAXD) were applied in situ during cyclic tensile tests of antler bone to quantify the strain placed on non-mineralized and mineralized collagen fibrils only 100 nm thick. Repeated cycles of loading and unloading led to the accumulation of permanent plastic strain within the fibrils.
The researchers formulated a two-level staggered model to explain the tensile response observed. When the antler bone is first loaded, bonds between the collagen and mineral within the fibrils are broken, causing inelasticity on the macroscopic scale. During continued tension, the antler remains deformed because of frictional sliding at the interface between mineral and collagen, leading to permanent plastic strain at the level of both the fibril and the tissue.
Editor’s comment: The authors propose an intrafibrillar sliding model between fibril and mineral to explain macroscopic yielding, assuming that the higher levels of organization do not contribute to this process.
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