Properties of Highly Porous Hydroxyapatite Obtained by the Gelcasting of Foams

Open-cell hydroxyapatite (HA) foams, produced through the novel technique of gelcasting foams with relative porosities ranging from 0.72 to 0.90, were characterized for pore-size distribution, surface area, permeability, compressive strength, elastic modulus, and microstructural features. The porous structure, which is composed of an array of spherical cells interconnected through windows, had a mode pore diameter in the range 17–122 μm, as demonstrated by mercury porosimetry. The BET specific surface area increased from 1.5 to 3.8 m²/g as the sample porosity increased. The compressive strength and elastic modulus were in the range 1.6–5.8 MPa and 3.6–21.0 GPa, respectively. The permeability constants, k ₁ (Darcian) and k ₂ (non-Darcian), were strongly dependent on porosity fraction and varied widely, from 1.22 × 10^?11 to 4.31 × 10^?10 m² and from 1.75 × 10^?6 to 8.06 × 10^?5 m, respectively. This combination of properties make the HA foams suitable for a variety of potential applications in the biomedical field, preferentially nonloading, including materials for bone repair, carriers for controlled drug-delivery systems, and matrixes for tissue engineering.