Piezoelectric response of bone in the MHz range

The healing mechanism of bone fractures by low intensity ultrasound is not yet to be fully understood. As one possible initial process of this mechanism, we focus on the piezoelectricity of bone and demonstrate that bone can generate electrical potentials by ultrasound irradiation in the MHz range. We have fabricated ultrasonic bone transducers using bovine cortical bone as the piezoelectric device. Electrical potentials induced by the ultrasound irradiation were obtained from all transducers. The electrical potentials changed as a function of time during immersed ultrasonic measurements and became stable when the bone was fully wet. The sensitivities of bone transducers were around 1/1000 of a poly(vinylidene fluoride) ultrasonic transducer and did not depend on the magnitude and alignment of hydroxyapatite crystallites in bone. In addition, the magnitude of the induced electrical potentials changed owing to the microstructure in the cortical bone. The potentials of transducers with haversian structure bone were higher than those of plexiform structure bone, which informs about the effects of bone microstructure on the piezoelectricity.