Oscillatory and step response electromechanical phenomena in human and bovine bone

Abstract Bone generates electrical potentials or strain-related potentials when mechanically deformed. These electrical potentials may be partially responsible for the remodeling process which bone experiences in response to mechanical loads. A large body of evidence suggests that streaming potentials are the dominant mechanism responsible for strain-related potential generation in fluid saturated bone. Recently, biphasic poroelastic theory has been coupled to electrokinetic theory in an attempt to further elucidate this mechanism. The work reported here expands the experimental evidence in support of this theory. Experimental results which characterize electrical and mechanical phenomena in both wide frequency oscillatory and step response testing of 47 human and bovine bone specimens are reported. These results also include data from experiments in which the viscosity and conductivity of the solutions permeating 10 human and bovine bone specimens were varied. A specially designed mechanical spectrometer and data acquisition system was used to perform oscillatory and step response mechanical testing of bone specimens. Testing procedures, which were optimized for strain-related potential measurement, were developed. These included procedures for varying testing solution viscosity and conductivity. The experimental data was analyzed using descriptive and inferential statistical techniques and linear and nonlinear regression methods. The following objectives were established for the work reported here: (1) to confirm the existing experimental results; (2) to attempt to obtain a successful correlation between theoretically predicted and experimentally observed mechanical phenomena; (3) to extend the experimental results over the wider frequency range of 0.05–100 Hz; (4) to test the theory in the time domain; (5) to test the theory for changes in viscosity and conductivity of the permeating fluid; and (6) to extend the experimental testing to include human bone specimens. All of these objectives were met except that a highly variable correlation between the theoretically predicted and experimentally observed mechanical phenomena was obtained. Patterns in these data are explored and the possible causes of the highly variable correlation are discussed. The results strongly suggest an electrokinetic origin for the observed electrical potentials. The microporosity of bone appears to be the location in which this mechanism operates.