Characteristics of the Stress-Generated Electrical Potentials in Bone Induced by Mechanical Loading

Abstract

Since the discovery of stress-generated potentials (SGPs) in bone by Fukada and Yasuda in 1957, researchers have tried to understand their origin and function in the maintenance of bone. There have been a variety of methods attempting to quantify these SGPs in both wet and dry bone. In this study, I prepared both dry and wet beams of cortical bovine bone and subjected them to mechanical deformation in cantilever bending. Mechanical testing was performed to explore how the magnitude of the SGPs was affected by hydration levels, strain, and pressure gradients associated with various load magnitudes and deformation rates. Signals that were collected from the dry bone samples were attributed to motion artifact resulting from the movement of the materials testing machine and load cell. The SGPs from wet bone, on the other hand, consistently produced exponentially decaying signals following deformation that were maintained throughout held deformation and produced an SGP of opposite magnitude upon release of deformation. The exponentially decaying SGP signal produced after application of a step load to wet bone samples was determined to fit a two-term exponential equation (V(t) = Aet/τ1 + Cet/τ2). The first term, made up of the A-coefficient and τ1, was found to be dependent on deformation rate whereas the second term, containing the C-coefficient and τ2, was dependent on load magnitude. The sum of the two coefficients determine the maximum voltage the SGP can reach. Additionally, samples were left to air dry for one hour and tested intermittently throughout that time period. SGP signals diminished significantly over the hour, therefore, it has been concluded that the majority of the SGP signal is due to streaming potentials caused by ionic fluid movement within the bone upon deformation.