Simulation of ultrasonically induced electrical potentials in bone

Low-intensity pulsed ultrasound treatment is known to shorten the healing period of bone fractures by 30%-40%, but the initial mechanism of the healing process remains unknown. One possible mechanism is related to the piezoelectricity of bone. However, the complex geometry of bones results in inherent challenges to evaluating electric fields induced therein. Therefore, in this study, we investigate the piezoelectric responses of bones by using simulations to study the wave propagation and induced potentials in bone, according to the piezoelectric finite-difference time-domain (PE-FDTD) method. First, we verify the suitability of the PE-FDTD method by comparing the simulated electric field results with the experimental data obtained by an ultrasound receiver using bone as the piezoelectric element. Next, ultrasound irradiation into a real bone model (the radius of a 66-year-old woman) is simulated at different incident angles. At normal incidence and off-axis incidence (45°), the maximum electric field strength was 4.3 and 5.6 mV/cm, respectively. We also present evidence of significant shear wave contribution to the induced potential. The results of this study confirm the existence of ultrasonically induced potentials in heterogenous bones with complex shapes, equal in magnitude to potentials generated in electrically stimulated bone healing.