Research Of Compatibility Of Dynamic Mechanics Of Bone Substitute Materials

With the development of science and technology, artificial biomaterials are more and more employed as substitutes implanted in bodies for replacing the injured human tissue. Now, hydroxyapatite (HA), as a bone substitutes, has been becoming one of the research focuses of biomaterials, for its good biocompatibility, avirulence, biological activity and osteo-conductivity. Its content and porous structure is similar to bone, so it is considered as ideal bone substitute.If the artificial hydroxyapatite were implanted into body it would either have biocompatibility or mechanical compatibility. The final mechanical properties of the hydroxyapatite in vivo are concern with its mechanical properties in vitro. After the substitute are implanted into body, on one hand it will be absorption and biodegradation by body , on the other hand bone tissue grow in it, its strength and rigidity increases. Then it becomes a part of bone in vivo. If its mechanical properties in the substitute materials consists with surrounding bone, it will has the same function as bone, which is so called mechanical compatibility. Otherwise, negative results will occur. For example, if the rigidity of implanted materials is bigger than that of bone, stress shield phenomena will happen and cause osteoporosis. Contrary, if the rigidity of it is smaller than bone, it will not bear loading as bone does.The purpose of this paper is to investigate the mechanical compatibility of hydroxyapatite then, split Hopkinson pressure bars technique (SHPB) was employed to measure the dynamic mechanical properties of HA. The hard ware and software of this apparatus were improved for fitting to measure mechanical properties of HA with relative low wave resistance. The tested material-hydroxyapatite is made by hydrothermal exchange based on natural coral, for its porosity is proper to bone cell grown in. HA, bone with and without organic components were tested by SHPB, and their stress-strain relationships, Young's moduli, ultimate stress, were obtained. The test results show that the apparent Young's moduli of HA, bone with and without organic component are 5.94±0.66 GPa, 12.29±1.62 GPa and 15.14±0.44 GPa respectively. The average ultimate stress are 45.11±2.92 MPa, 115.80±7.80 MPa and 237.8±18.42 MPa respectively. In order to simulate the condition of bone cell growing in HA in vivo, the bone cell were cultured on HA for 10 days. Its Yong's modulus and ultimate stress were also tested by SHPB.