Study on Ultrasound Irradiation Induction of Electrical Potentials in Bone

Objective: It is well known that applied stress induces electrical potentials in bone. We have experimentally studied whether induced potentials could be found in bone using an ultrasound irradiation system similar to low-intensity pulsed ultrasound (LIPUS). Materials and Methods: Circular plate specimens (diameter 10 mm, thickness 1 mm) were obtained from bovine femora in order to determine if bone behaved as a piezoelectric material. Using these specimens, ultrasound receivers were fabricated. The irradiation of an ultrasound pulsed wave (amplitude 5 kPa, around 1 MHz) induced weak electrical potentials that were almost 0.1% of that observed with conventional ultrasonic transducers using piezoelectric polymer films. Results and Discussion: The induced potentials clearly depended on the angle between the direction of the irradiation and the direction of the bone axis and showed a maximum when the angle was 45 degrees. It is known that the ultrasonic wave velocity changes due to the propagation direction and shows anisotropy. The behavior of induced potentials, however, was different from the anisotropy of wave velocities. These results tell us that the amount of induced electrical potentials possibly changes depending on the direction of the ultrasound wave produced by the LIPUS system.