Mechanical spectroscopy of bovine compact bone

Aging is characterized by a progressive degradation of the mechanical properties of bone that seems to be due to an increase in porosity and an alteration of the extracellular matrix. From a biomechanical point of view, the alteration of the bone extracellular matrix is hypothesized to affect its viscoelastic properties in a significant way. In this context, mechanical spectroscopy was used to study the viscoelastic behavior of bovine compact bone, chosen here as a reference material. The mechanical loss spectrum of this tissue exhibits a continuous increase in damping associated with a decrease in the shear modulus either as a function of temperature between 300 and 350 K or when frequency is decreased from 5 to 5 mHz in isothermal conditions. From the “frequency–temperature” shifts, it was possible to deduce values of 130 and 89 kJ/mol for the activation enthalpy in dry and wet bone, respectively. Thermal cycling up to 420 K leads to an irreversible change of the viscoelastic properties that is interpreted by degradation of the collagen phase.