Abstract:
The organic matrix phase of bone plays important role in its mechanical performance, especially in the post-yield
regime. Also, the organic phase influences loading rate-dependent behaviour of bone which is relevant during the
high-speed loading events. Many diseases, as well as aging, affect the matrix phase of bone which causes
compromised mechanical properties. Improved understanding of alterations in the organic matrix phase on
mechanical response of bone will be helpful in the mitigation of fractures associated with inferior matrix quality.
In the present work, effect of alteration in organic matrix of cortical bone on its strain-rate dependent behaviour
was investigated. To produce different amounts of collagen denaturation, bovine cortical bones were heated at
the temperature of 180 ◦C and 240 ◦C. Further, compression testing was performed at quasi-static strain rates of
10− 4 s
− 1 to 10− 2 s
− 1 using a conventional testing machine whereas a modified Split Hopkinson Pressure Bar
(SHPB) was used for high strain rate (~103
) testing. Thermal treatment-induced changes in the mineral and
organic phases of bone were assessed using X-ray diffraction (XRD) and Fourier-transform infrared-attenuated
total reflection (FTIR-ATR) techniques respectively. Compression test results show that thermal treatment of
bone up to 180 ◦C did not affect mechanical properties significantly whereas treating at 240 ◦C significantly
reduced elastic modulus, failure stress and failure strain. Also, thermal denaturation of collagen reduced the
strain rate sensitivity of cortical bone at high strain rates. Similar to the compression test observations, nanoindentation results show a significant reduction in elastic modulus and hardness of denatured samples. Further,
FTIR results revealed that with the heat treatment of bone, collagen structure undergoes conformational changes
at the molecular level. The initial helix structure breakdowns into unordered/random coil structures which
subsequently reduced the mechanical competence of bone. The present study provides insight into the effect of
organic matrix modification on mechanical behaviour of cortical bone which could be helpful in understanding
bone disorders associated with organic matrix phase and development of therapeutic interventions.
