Collagen and bone viscoelasticity: A dynamic mechanical analysis

The purpose of this study was to explore the effects of changes in Type I collagen on the viscoelasticity of bone. Bone coupons were heated at either 100 or 200 °C to induce the thermal denaturation of Type I collagen. Half of these specimens were rehydrated after heat treatment; the other half were tested in a dry condition. The degree of denatured collagen (DC%) was analyzed by a selective digestion technique with the use of α-chymotrypsin. Isothermal (37 °C) and variable temperature tests (scans from 35 to 200 °C) were performed with the use of a dynamic mechanical analyzer to evaluate changes in bone viscoelastic properties as a function of collagen damage, specifically, changes in the loss factor (tan δ) and storage modulus (E′) were assessed. Significant collagen denaturation occurred only when bone was heated at 200 °C irrespective of the hydration condition. Also, DC% did not show a significant effect on tan δ. However, higher values of tan δ were observed in wet samples compared to dry specimens. The temperature-scan tests revealed that the hydration condition, but not DC%, significantly affected the behavior of tan δ. However, E′ was not strongly influenced either by DC% or by water content. These results suggest that at a constant frequency the denaturation of collagen triple-helical molecules may have few effects on the viscoelasticity of bone, but moisture may play a prominent role in determining this property.