Induced electric potential in cortical bone and cartilage by ultrasound irradiation

LIPUS (low intensity pulse ultrasound) can reduce the time of bone fracture healing. The detailed mechanism of ultrasonic effects on bone, however, has not been clearly understood yet. One possible idea seems to be the piezoelectricity of bone. The purpose of this study is to evaluate the piezoelectricity of cortical bone and cartilage. In order to evaluate piezoelectricity of bone in the MHz range, bone transducers were fabricated. Circular plate cortical bone samples and cartilage samples (diameter; 10.0 mm, thickness; 1.00 mm) were used as piezoelectric materials of the transducer to receive ultrasound. The surface of bone plates was normal to the bone axis or the radial axis and that of cartilage plates was normal to bone axis. By irradiating ultrasound in the MHz range, induced electric potentials were successfully observed in all transducers. The maximum sensitivity of the cartilage transducer was about 93.6 nV/Pa and that of the bone transducer was about 27.5 nV/Pa. Induced electric potentials of cartilage transducers were always larger than those of bone transducers. The main part of the cartilage is type collagen. The results may indicate that the piezoelectricity of the cartilage and bone mainly comes from the collagen.