Microdamage induced collagen denaturation in bone

Age related fragility fractures of bone are a major issue in health care of our aging populations. In addition to the mineral phase, the collagen network in bone plays a significant role in imparting the toughness to the tissue. However, the underlying mechanism is still poorly understood. The hypothesis of this study is that microdamage accumulation may causes damage in the collagen phase of bone, which is reflected by the increased amount of denatured collagen molecules. To test the hypothesis, a protocol using a selective digestive technique was first adopted, modified, and then used to determine the amount of denatured collagen in bone. Human cadaveric bones were procured from femoral diaphysis of middle aged and elderly male donors. To test the selective digestion protocol, the bone samples (5mmx5mmx0.5mm) were heated at different temperatures to induce different degrees of collagen denaturation. The amount of denatured collagen was determined using the protocol, which was verified by comparing its results with the known values reported in the literature. Next, compression test specimens (3mm in diameter and 5mm long) were prepared from the same donors and mechanically tested till failure. The microdamage density and collagen denaturation in the specimens were estimated and the correlation between microdamage and collagen denaturation was determined. The data showed that there was a significant difference in control and damaged samples for percentage of denatured collagen and microdamage densities. The data also showed that a significant correlation was found between the percentage of denatured collagen and the density of cross hatch damage, but not with linear cracks and diffuse damage. This suggests that collagen denaturation induced by mechanical testing is a possible mechanism for energy dissipation process. Since more energy dissipation capacity gives more toughness to bone, enhancing the properties of collagen may make the bone tough.