Experimental Study On The Coupling Between The Piezoelectric And Streaming Potentials In Wet Bone

The mechanical and electrical properties of bone are the properties of stress generating potentials in bone,including piezoelectric and streaming potentials,which are collectively referred to as stress generated potentials(SGPs).SGPs are one of the mechanisms that stress affects bone remodeling or bone growth,and also an important research content in the field of bone mechanics.In order to study the effect and mechanism of SGPS on bone remodeling,in this study,the coupling relationship between the piezoelectric and streaming potentials was investigated experimentally and theoretically in wet bone(bone immersed in buffer solution),which was similar to living bone in physical and chemical environment.The main work includes the following aspects:1.In order to achieve the simultaneous measurement of the piezoelectric and streaming potentials in wet bone,a testing system to measure the both potentials was developed.The test system uses a bidirectional loading method to apply concentrated load and liquid pressure on wet bone,and can measure the piezoelectric or streaming potentials in wet bone individually or simultaneously.The accuracy of this system in measuring SGPs was verified,laying the experimental foundation for further research on the coupling relationship between piezoelectric potential and streaming potential in bone.2.A special phenomenon was found that streaming potential increases linearly with time under constant fluid pressure gradient.According to the viscoelastic properties of bone and the uneven charge distribution in bone,the effects of viscoelastic properties of bone,solid surface charges in bone and radial dimension of microchannel on streaming potential were analyzed.It was determined that the change in streaming potential with time was caused by nonuniform surface charge accumulation in microchannel of bone samples.A theoretical model of uneven distribution of surface charge density in capillaries in bone was proposed.On this basis,the phenomenon that streaming potential is directly proportional to the channel length in the area with high charge density and increased linearly with time due to nonuniform surface charge accumulation in the microchannel of bone samples under maintained liquid pressure was explained.It was proved that the streaming potential in Haversian canals,lacunae and tubules was not affected by the electroviscous resistance in the fluid,while the streaming potential around osteocytes in the bone lacuna might be affected by the electroviscosity.3.Through an experimental study of the coupling effect of the piezoelectric and streaming potentials in bone,the piezoelectric and streaming potentials in bone samples under concentrated load and liquid pressure were measured using the developed test system.By changing the embedding,crossing order and amplitude of concentrated load and liquid pressure,the experimental conditions of 4 loading combinations were designed,and the changing rules of peak value and curve slope of the piezoelectric and streaming potentials in bone samples under the simultaneous effect of concentrated load and liquid pressure were obtained.The results show that under constant liquid pressure,the potential curve of bone increased with time,and its rising rate decreased with the increase in concentrated load.However,influenced by liquid pressure,the peak potentials of bone samples corresponding to the rising and falling edges of concentrated load would reduce,demonstrating that under the experimental conditions,the coupling effect of the piezoelectric and streaming potentials in bone does not change the waveform of each other,but only changes the amplitude of each other.Based on the conduction current circuit,the equivalent electrical relationship under the coupling of piezoelectric and streaming potentials was established.Based on the theoretical analysis of the equivalent electrical relationship,the basic rule that both streaming and piezoelectric potentials can cause space-charge polarization,thus affecting the charge distribution in wet bone and changing the electrical properties of solid and liquid phases is clarified.These results are helpful for understanding the dependence of bone growing on the electric signals and of positive action on clinic application and medical instrument development.