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 mum, as demonstrated by mercury porosimetry, The BET specific surface area increased from 1.5 to 3.8 m(2)/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 x 10(-11) to 4.31 x 10(-10) m(2) and from 1.75 x 10(-6) to 8.06 x 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.