| Controversy exists over the source of strain induced polarization in bone. The debate has spanned five decades and in recent years most authors have focused their attention on the promise of streaming potentials. However, there is strong evidence that traditional piezoelectricity contributes to polarization in bone. But there is also evidence in the literature that piezoelectricity does not act alone. At low frequencies the piezoelectric response was found to be on the order of 100 times greater than at high frequencies in the d31 axial coefficient. When the literature is considered as a whole this disparity is apparent. There is convincing evidence that piezoelectricity acts in conjunction with Maxwell-Wagner effects. Presented here is an examination of the prospect that classic piezoelectricity and Maxwell-Wagner effects are responsible for the disparity observed. Considerable effort is dedicated to detecting the small deformations in bone and distinguishing usable data from electromagnetic and mechanical noise. Because of the sensitivity limitations of the equipment used in the present experiment, only the d14 coefficient was measured. Strong frequency dependence was observed in both the real and imaginary coefficient values. However, the experimental results show no evidence of Maxwell Wagner like dispersion. This is possibly due to the elimination of the microcapillary regions of water. While dry bone is still a composite material composed of mineral and collagen, it is most likely that the Maxwell-Wagner effects, if present, happen at the interface between the pockets of water in bone and the organic regions of hydrated bone. |
