Stress-whitening occurs in demineralized bone.
BACKGROUND
The incidence of age-related bone fracture is increasing with average population age. Bone scatters more light (stress-whitens) during loading, immediately prior to failure, in a manner visually similar to polymer crazing. We wish to understand the stress-whitening process because of its possible effect on bone toughness. The goals of this investigation were a) to establish that stress-whitening is a property of the demineralized organic matrix of bone rather than only a property of mineralized tissue and that stress whitening within the demineralized bone is dependent upon both b) hydrogen bonding and, c) the orientation of loading.


METHODS
Demineralized cortical bone specimens were loaded in tension to failure (0.08 strain/s). The effect of hydrogen bonding on mechanical properties and the stress-whitening process was probed by altering the Hansen's hydrogen bonding parameter (δh) of the immersing solution.


RESULTS
Stress-whitening occurred in the demineralized bone. Stress-whitening was negatively correlated with δh (R(2)=0.81, p<0.0001). Stress-whitening was significantly lower (p<0.0001) in specimens loaded orthogonally compared to those loaded parallel to the long (strong) axis.


CONCLUSIONS
The stress-whitening observed was consistent with increased Mie scattering. We suggest that the change in Mie scattering was due to collagen fibril dehydration driven by the externally applied stress. The presence of stress-whitening in demineralized bone suggests that this process may be a property of the collagenous matrix and hence may be present in other collagenous tissues rather than an emergent property of the bone composite.
Lawrence J Ellison Musculoskeletal Research Laboratory, Department of Orthopaedic Surgery, UC Davis School of Medicine, UC Davis, Sacramento, CA, USA; Biomedical Engineering Graduate Group, UC Davis, Davis, CA, USA.
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Hardisty
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Garcia
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Choy
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Dahmubed
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Stover
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Fyhrie
D000818:Animals; D001696:Biomechanical Phenomena; D018488:Bone Demineralization, Pathologic / Q000503:physiopathology*; D055119:Elastic Modulus; D006736:Horses; D013314:Stress, Mechanical
Biomechanics; Cortical bone; Hansen's hydrogen bonding potential; Optics; Scattering; Stress-induced whitening