The origin of stress-generated potentials in fluid-saturated bone.

The objective of this study was to determine the origin of stress-generated potentials (SGPs) in fluid-saturated bone. Stress-generated potentials were studied as a function of the conductivity, NaCl concentration, and viscosity of the fluid contained within cortical human and bovine bone. Bone samples were soaked in solutions in which NaCl and sucrose concentrations were systematically varied. Macroscopic SGPs and their relaxation times were measured as a function of these properties. Stress-generated potentials were also measured as a function of conductivity and NaCl concentration by using a microelectrode. The results of this study confirmed that the properties of the fluid in bone have a great influence on the magnitude and time dependence of the SGP. Especially notable was the observation that solutions of high NaCl concentration consistently reversed the polarity of the SGP. These results are consistent with streaming potential theory. Although fluid-saturated bone may retain some piezoelectric properties, SGPs are predominantly caused by streaming potentials.