Experimental study of time response of bending deformation of bone cantilevers in an electric field

Bone is a complex composite material with hierarchical structures and anisotropic mechanical properties. Bone also processes electromechanical properties, such as piezoelectricity and streaming potentials, which termed as stress generated potentials. Furthermore, the electrostrictive effect and flexoelectric effect can also affect electromechanical properties of the bone. In the present work, time responses of bending deflections of bone cantilever in an external electric field are measured experimentally to investigate bone's electromechanical behavior. It is found that, when subjected to a square waveform electric field, a bone cantilever specimen begins to bend and its deflection increases gradually to a peak value. Then, the deflection begins to decrease gradually during the period of constant voltage. To analyze the reasons of the bending response of bone, additional experiments were performed. Experimental results obtained show the following two features. The first one is that the electric polarization, induced in bone by an electric field, is due to the Maxwell-Wagner polarization mechanism that the polarization rate is relatively slow, which leads to the electric field force acted on a bone specimen increase gradually and then its bending deflections increase gradually. The second one is that the flexoelectric polarization effect that resists the electric force to decrease and then leads to the bending deflection of a bone cantilever decrease gradually. It is concluded that the first aspect refers to the organic collagens decreasing the electric polarization rate of the bone, and the second one to the inorganic component influencing the bone's polarization intensity.