Research Of Streaming Potentials In Bone And Mechanical Compatibility Of Bone Substitutes

The electromechanical behaviour of bone, called stress generated potentials (SGP), includes piezoelectric effect and streaming potentials. When external loads are applied to bone, it deforms and causes fluid pressure to build up in its microchannels. The pressure gradient between different portions of the bone microchannels, such as Haversian canal and canaliculi, causes fluid flow through them and then streaming potentials occurs. Since human bone bears dynamic loading generally, determining the streaming potentials induced by the dynamic loads is helpful for understanding electric environment around bone cells.The streaming potentials were first measured with the loading pressure controlled in positional model, which can not make the pressure increase linearly with time. The results suggest that the stable values of streaming potentials depend on the pressure loading rates. The faster the pressure increase the lower the stable values of streaming potentials are.In order to confirm the conclusion, the experimental setup was modified to make the pressure to be controlled in pressure model, which can't make the pressure increase linearly with time. Then the similar experiments were conducted at two predefined conditions. The first condition is that the fluid flows through all kinds of microchannels sample and the second one is that the lateral surface of the samples is coated with silica gel which prevent the fluid flowing through the channels in transverse direction. The streaming potentials were obtained under the five pressure loading rates at the two predefined conditions.The results show that the amplitudes of the streaming potential depend on pressure loading rates for both coated and uncoated samples. When the lateral surfaces of samples are coated with the silica gel, streaming potentials decrease over 50%. In other wards, the flowing of the fluid through canalicul can generate the streaming potential over 50%, while it generates below 50% when the fluid flows through the Haversian canals. It indicates that the microchannels running transverse to osteon such as canaliculi contribute more streaming potentials than those along the osteon such as Haversian canal.The origin that stable values of streaming potentials depend on the pressure loading rates was considered to be caused by as turbulent flow in the microchannels. For verifying this issue, a numerical simulation calculation was performed, using the FLUENT software. The simulation demonstrates that turbulent flow occurs near the rough inner wall surfaces and the higher pressure loading rate the more turbulent circulations.Another study of the dissertation concerns the mechanical compatibility of bone substitute—hydroxyapatite. In order to find out the influence of soft tissues on Young's modulus of the artificial HA after implantation, HA samples were implanted into the rat back muscles and taken out after 20,40,60 and 80 days,respectively. Young's moduli of the implanted samples were measured using digital image correlation technique. The results show that Young's modulus increased by 28.83% 20 days after implantation and then the increase amplitude became weak.