Fabrication of octacalcium phosphate foams with suitable mechanical strength for use as a bone substitute based on the setting reaction of acidic calcium phosphate granules

Octacalcium phosphate (OCP) blocks are attractive feedstocks for new biomaterials because of their excellent biocompatibility. Attaching an interconnected porous structure (i.e., a foam) is a good way to use OCP as a bone substitute because this structure allows tissue penetration in the materials. However, the foaming structure shows a lower mechanical strength compared to block-formed materials. In this study, we fabricated OCP foams with enough mechanical strength from calcium dihydrogen phosphate granules of different sizes (100–250, 250–500, 500–1000, and 1000–2000 µm) through a setting reaction using an acidic phosphate solution and a phase-conversion process. The fabricated OCP foams were found to have high enough mechanical strength (>0.5 MPa in diametral tensile strength) and porosity (∼70 %). For small granules, a relatively low concentration of acidic phosphate solution was suitable for the setting reaction.