Effects of X-ray irradiation on load partitioning between the constituent phases of cortical bone

Abstract

Event Abstract Back to Event Effects of X-ray irradiation on load partitioning between the constituent phases of cortical bone AC Deymier-Black1*, A Singhal1, F Yuan1, JD Almer2, SR Stock3, LC Brinson4 and DC Dunand1 1 Northwestern University, Department of Materials Science and Engineering, United States 2 Advanced Photon Source, Advanced Photon Source, United States 3 Northwestern Universit, Department of Molecular Pharmacology and Biological Chemistry, Feinberg School of Medicine, United States 4 Northwestern Universit, Department of Mechanical Engineering, United States X-ray Irradiation is known to have significant effects on the fracture properties of cortical bone due to the cross-linking and degradation of collagen [1]. However, no information exists on the effect of x-ray irradiation on the partitioning of load between the stiffer hydroxyapatite (HAP) and the weaker collagen phases of bone, which is dependent on the quality of the interface between the two phases. Here, we use a combination of small and wide-angle high-energy x-ray scattering to measure the HAP and fibrillar strains (and thus loads) of bovine bone, as has been previously done on bovine dentin [2], under various compressive loading schemes and at different doses of x-ray irradiation. {BR} As the x-ray dose increases, we find a decrease in both the HAP residual strain and the elastic strain carried at steady state during bone creep deformation under a compressive load. This load shedding by the HAP platelets suggests that damage at the HAP-collagen interface limits the efficiency of load transfer. However, the load carrying capacity of HAP during rapid load-unload experiments (unlike long-term creep experiments) shows no change with increasing irradiation levels. {BR}This combination of HAP load bearing behaviors might be caused by reversible interfacial damage, rather than irreversible collagen cross-linking. The interfacial bond between the HAP platelets and the collagen is mainly composed of weak electrostatic bonds. Decarboxylation of the collagen side chains upon irradiation is known to lead to bond breakage [3], allowing relaxation of the HAP strain. We hypothesize that these same weak bonds are also easily reformed, allowing the interface to regain its original load transfer abilities. {BR}