Fabrication of pure octacalcium phosphate blocks from dicalcium hydrogen phosphate dihydrate blocks via a dissolution–precipitation reaction in a basic solution

Octacalcium phosphate (OCP) blocks are attractive as bone substitutes because of their excellent biocompatibility. They can be fabricated from precursor ceramic blocks via a compositional conversion process. Herein, high-purity OCP blocks were fabricated through a dissolution–precipitation reaction from precursor blocks of dicalcium hydrogen phosphate dihydrate (DCPD) immersed in a 1.00-mol/L basic phosphate solution of disodium hydrogen phosphate (NaAP; pH ∼ 9) at 70 °C for 2 days. The results showed that they were completely converted to OCP blocks comprising interlocking ribbon-like crystals while maintaining their shape. The diametral tensile strength of the obtained OCP blocks was ∼6 MPa, which was significantly higher than that of OCP blocks fabricated from calcium sulfate as the precursor.