Research Of Static Mechanical Compatibility Of Bone Substitute-Hydroxyapatite

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 should either have biocompatibility or mechanical compatibility. 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 mechanical properties of the substitute materials consists with surrounding bone, it will has the same mechanical 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 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 mechanical properties of hydroxyaptite were tested by digital image correlation technique(DIC),in order to investigate the static mechanical compatibility of hydroxyapatite. The material-hydroxyapatite tested is made by hydrothermal exchange based on natural coral, for its porosity is proper to bone cell grown in. The stress-strain curves of the hydroxyapatite was obtained. Both Young's modulus and Poisson's ratio can be obtained. Bone with and without organic components were also tested by DIC. The results show that the apparent Young's moduli of HA, bone with and without organic component are 10.91±0.89 GPa, 20.35±1.58 GPa and 12.66±1.78 GPa respectively. The average ultimate stress are 14.02±2.01MPa, 207.06±7.14MPa and 42.33±2.43MPa respectively. The Poisson's ratio are 0.244±0.025, 0.222±0.035, 0.132±0.033. In order to simulate the condition of HA in vivo, the osteoblastic have been cultured on HA for 10 days and HA have been implanted in rat subcutaneous for 20, 40, 60days. The mechanical properties of HA were also tested by DIC.The results show that osteoblast and subcutaneous tissues can increase Young's modului and compressive strength of hydroxyaptite.