Experimental Research On Signal Characteristic Of Piezoelectric Voltage In Bone

The researches on electromechanical behavior of bone for determining the relationships between voltages and bone remodeling are based on the understanding of how the potentials generated by stress influencing the bone cell growth. Usually, the polarized charges, generated by stress, in the bone distribute ununiformly. This charge distribution makes an ununiform distribution of voltage which my impact on the remodeling of bone. Because there are microcracks in bone and stress concentration on the crack tips, the piezoelectric voltages may higher than other positions in bone. This kind of voltages may speed or reduce the crack extension. Therefore, it is necessary to determine the voltage distribution by experiments.This paper developed a testing system for measuring the piezoelectric voltage on the surface of bone, which was composed of Instron1343 fatigue testing machine and BMA-931 bioamplifier. A double metal electric shields technique is employed for shielding electromagnetic interference. Then, reliable piezoelectric voltages in dry bovine shinbone are obtained.The tested waveform of piezoelectric voltages under trapezoid loading wave shows that there is relaxation during loading and load keeping by the charge releasing. The relaxation time constant during load increasing is not the same as the one during load keeping. The waveforms of piezoelectric voltage were simulated by a model function which was very close the tested piezoelectric voltage curve. It is found that the time constant of loading process is smaller than the one in the load keeping process. More than that, a exponent coefficient is also required to describe characteristic of the relaxation curve during loading because of the relaxation time constants are different from one position to another in bone.The influences of relative humidity of environment to piezoelectric voltage in bone were also studied by experiments. Piezoelectric signals of bone are tested at different humidity. Test results show that piezoelectric voltage of bone decrease with increasing humidity. The piezoelectric charge also decreases with increasing humidity at relative low decreasing amplitude however. In order to determine the influence of shear stress on piezoelectric voltages in bone, three and four point bending experiments of bone specimens are conducted for measuring the piezoelectric voltages in the two kinds of deformation. By comparing the tested results, it is concluded that the sign and amplitude of the piezoelectric voltages are mainly dominated by shear stress. Normal stress can also generate piezoelectric voltages, but with weaker effect.The final tests were applied to measure the piezoelectric voltages in bone around a notch with different length. The result illustrate that the piezoelectric voltages decrease with length of the notch. The results were attributed to stress changes and stress concentration.