Bone Abstracts

Bone is a tough composite material, comprised of a compliant collageneous matrix, brittle apatite mineral crystals and a suite of non-collageneous proteins (NCPs). Bone material properties depend on these components, and their interactions at the mineral-collagen interface. ‘Bone mineral density’ (BMD), a parameter used to predict fracture risk, is routinely quantified by DEXA. Previous studies used ex vivo emu tibiae as a model to test the effect of organic component quality on BMD and material properties. Endocortical infusion with 1 M KOH caused no change in BMD, but reduced the three-point bending failure stress, and increased the failure strain. These changes were attributed to in situ collagen degradation, and possibly denatured NCPs, which could weaken the mineral–collagen interface. In this study, the ex vivo emu tibial model was used to test the effects of weakening the interface between bone mineral and collagen. It was assumed that the electrostatic attraction between positively charged bone minerals and electronegative domains of some NCPs is the primary chemical bond between the inorganic and organic components of bone. It was hypothesized that small, electronegative fluoride ions (F-) could migrate to the positively charged apatite surface, and disrupt this electrostatic bond. Endocortical F-infusion should not affect BMD, and would be expected to increase the post-yield material properties in 3-point bending, as yielding occurs at the periosteal bone that was not exposed to F-. Emu tibiae were endocortically infused with 0, 0.05, 0.1, or 1 M NaF at neutral pH for two weeks. The BMD, elastic modulus, yield stress/strain, ultimate stress, and failure stresses showed no statistical difference. However, increased post-yield strain and failure strain, coupled with a decreased endocortical hardness of the F-treated bones, suggest a role for mineral-collagen interface strength that is not detected by DEXA.