Controlled synthesis of magnesium whitlockite powder from amorphous calcium phosphate

Magnesium whitlockite (Mg-WH, Ca₁₈Mg₂(HPO₄)₂(PO₄)₁₂) is a calcium phosphate (CP) that has been identified as a potential material for use in hard-tissue applications due to its osteoconductive and resorbable properties. In this study, Mg-WH was synthesized at 80 °C via a dissolution-precipitation route using amorphous calcium phosphate (ACP) as a reactive precursor. The effects of phosphate buffer composition and magnesium ion (Mg²⁺) concentration on phase formation was systematically investigated to identify conditions yielding single-phase Mg-WH. Phase-pure Mg-WH was obtained using a 75:25 (v/v) mixture of NH₄H₂PO₄ and (NH₄)₂HPO₄ solutions, 17 mmol/L Mg²⁺ in the reaction medium, and 0.50 g of ACP. At different conditions, secondary phases were observed to form, primarily monetite (CaHPO₄) and dittmarite (NH₄MgPO₄·H₂O). The proposed approach provides a simple route to high-purity Mg-WH powder with promising features for further biomedical applications.