Stiffness compatibility of coralline hydroxyapatite bone substitute under dynamic loading

When hydroxyapatite bone substitutes are implanted in human bodies, bone tissues will grow into their porous structure, which will reinforce their strength and stiffness. The concept of mechanical compatibility of bone substitutes implies that their mechanical properties are similar to the bone tissues around, as if they were part of the bone. The mechanical compatibility of bone substitutes includes both static and dynamic behavior, due to the mechanical properties of bone depending on the strain rate. In this study, split Hopkinson pressure bar technique (SHPB) was employed to determine the dynamic mechanical properties of coralline hydroxyapatite, bones with and bones without organic components, and their dynamic stress-strain curves of the three materials were obtained. The mechanical effects of collagens in bone were assessed, by comparing the difference between the Young’s moduli of the three materials. As the implanted bone substitute becomes a part of bone, it can be regarded as an inclusion composite. The effective modulus of the composite was also evaluated in order to estimate its mechanical compatibility on stiffness. The evaluated result shows that the suitable porosity of HA is 0.8, which is in favor of both static and dynamic stiffness compatibility. Supported by the Tianjin Natural Science Foundation (Grant No. 05YFJMJC10500)