A broadband viscoelastic spectroscopic study of bovine bone: implications for fluid flow.

To explore the hypothesis that mechanical excitation-induced fluid flow and/or fluid pressure are potential mechanical transduction mechanisms in bone adaptation, a complementary experimental and analytical modeling effort has been undertaken. Experimentally, viscoelastic tan delta properties of saturated cortical bovine bone were measured in both torsion and bending, and significant tan delta values in the 10(0)-10(5) Hz range were observed, although the nature of the damping is not consistent with a fluid pressure hypothesis. Analytically, micromechanically based poroelasticity models were exercised to quantify energy dissipation associated with load-induced fluid flow in large scale channels. The modeling results indicate that significant damping due to fluid flow occurs only above 1 MHz frequencies. Together, the experimental and analytical results indicate that at excitation frequencies presumed to be physiological (1-100 Hz), mechanical loading of bone generates extremely small pore fluid pressures, making the hypothesized fluid-pressure transduction mechanism upon osteocytes untenable.