Labile Zn ions on octacalcium phosphate-derived Zn-containing hydroxyapatite surfaces

► Zinc (Zn)-containing octacalcium phosphate (OCP) and its hydrolyzed Ca-deficient hydroxyapatite (HA) were prepared. ► Zn release was investigated by comparing the solubilities of the crystals in physiological environments, such as medium. ► Some of Zn ions are present as a labile state on these calcium phosphate surfaces. ► Zn ions on the crystal surfaces are released if cysteine and histidine are present under co-existence of other amino acids.