Effect of Heat Denaturation of Collagen Matrix on Bone Strength

Abstract

Bone is often regarded as a composite material consisting of hydroxyapatite (HAp-like) mineral particles, organic matrix (mostly Type I collagen) in microscopic scale. The mechanical properties of bone at macroscopic scale depend on the structural organization and properties of constituents in the microscopic scale. It has been considered that bone density is a predictor of its strength from a macroscopic perspective, but denaturation of the organic matrix would also lead to a significant loss of bone strength. In this study, heat-treated bone was examined as a collagen denatured model, and then four-point bending tests and impact tests were conducted to assess the role of the collagen matrix for mechanical properties of bone. Cortical bone specimens were obtained from the mid- diaphyses of bovine femurs and heat treated in an oven for 2 hours at 100, 150, 180 and 200;C, respectively. The specimens were stored in saline until the experiments. The elastic modulus and bending strength caused by collagen denaturation were measured by four-point bending tests using a mechanical testing machine. The tests were performed up to fracture at a deflection rate of 0.5 mm/min, with an inner and outer span of 10 and 24 mm respectively. Toughness was evaluated by measuring fracture energy of the specimens using a self-made impact tester. As the results of four-point tests, the specimens heated at over 150;C failed with a low strain in the elastic region, suggesting a brittle fracture behavior. The elastic modulus of bone was slightly reduced with the heating temperature, whereas the bending strength significantly decreased, especially at 150;C. The results of the impact fracture test shows heat-induced collagen denaturation has great influence on the toughness of bone. These results suggest that not only denatured collagenmolecules but also collagen cross-links play an important role on the mechanical properties of bone.