Effects of irradiation and non-enzymatic glycation on the fracture resistance of bovine cortical bone

Abstract

Bone is a complex multi-phase composite having mechanical properties that are strongly dependent on its constituent parts. Components contributing towards the overall mechanical quality of bone include the organic phase (primarily Collagen I) and the inorganic phase (Hydroxyapatite). However, the individual contribution of each of the material phases towards crack propagation and the inherent fracture toughening mechanisms that are observed in bone are not well understood. Therefore, this study aims to investigate the contribution of the organic and inorganic constituents to the fracture resistance of cortical bone. Three treatment methods were selected that independently alter either the organic or inorganic components of cortical bone. The first two treatments effect the organic phase by denaturation of the collagen and formation of natural enzymatic cross-links from exposure to irradiation, and by incubation in a Ribose solution to induce Non-Enzymatic Glycation (NEG). The third treatment alters the inorganic phase by decalcification in ethyl-diamine-tetra-acetic acid (EDTA). Following treatment, the specimens were mechanically tested to obtain the fracture resistance curve as a function of crack growth using the unloading compliance method. To supplement this technique, stages of the crack growth were sequentially labelled using fluorochrome stains to observe the crack path as well as the toughening mechanisms (e.g. ligament bridging). Overall, the results of this study show that the organic phase is responsible for the toughening and fracture resistance behaviour of cortical bone while the inorganic phase contributes to its stiffness. The results of this study also suggest that the formation of natural enzymatic cross-links and protein denaturation due to irradiation are more detrimental to the fracture resistance of cortical bone than the non-enzymatic cross-links formed by NEG.