Strategy to reduce carbonate incorporation in the fabrication of hydroxyapatite nanopowders

Abstract

Coexistence of carbonate ions in aqueous solution often leads to difficulty in the preparation of stoichiometric hydroxyapatite (HAp), owing to formation of carbonate-containing HAp with low crystallinity. This study is focused on examining appropriate conditions to prepare HAp with reduced incorporation of carbonate through a wet processing in aqueous solution, starting from calcium chloride (CaCl₂) and trisodium phosphate (Na₃PO₄). Titration of Na₃PO₄ solution to CaCl₂ solution resulted in formation of crystalline HAp with low contents of carbonate, whereas titration of CaCl₂ solution to Na₃PO₄ solution resulted in formation of amorphous calcium phosphate that contains approximately 3 mass % of carbonate. The HAp particles prepared in a condition under coexistence of trehalose were finer and well-dispersed than those prepared in a solution free from trehalose. The addition of the Na₃PO₄ solution to the CaCl₂ solution contributes to nucleation of HAp with minimal carbonate incorporation.