Influence of microporosity and macroporosity on the mechanical properties of biphasic calcium phosphate bioceramics: Modelling and experiment

Macroporous biphasic calcium phosphate (BCP) bioceramics, for bone substitution applications, have been synthesized, cold isostatically pressed and pressureless sintered, using naphthalene particles as a porogen to produce macropores. The resulting materials are mixtures of β-tricalcium phosphate and hydroxyapatite with various microporosities and macroporosities. Mechanical properties (Young's modulus, compressive strength and fracture toughness) were measured on specimens over the widest attainable ranges of porosities, and compared to previously proposed analytical models and hypotheses. These models describe the evolution of the mechanical properties as functions of macroporosity and microporosity separately, the strength model considering macropores as critical flaws in the ceramic. Results show that the presence of macropores strongly influences the critical flaw size, but the latter appears to increase with macroporosity. This phenomenon can be explained by the presence of clusters of macropores, acting as critical flaws, becoming larger as macroporosity increases.