Brushite (DCPD, CaHPO4·2H2O) crystals are of great significance in a range of fields including biology, medicine, chemistry, and materials science. One important issue is the control of their morphology; when the crystal growth conditions are changed, the morphology and surface crystal conditions also change. The chemical reaction behavior depends strongly on the surface condition of the particles. Here, we report the effect of coexisting anions on the morphology control of DCPD particles. We synthesized the particles through a liquid-phase reaction by mixing a starting solution of ammonium dihydrogen phosphate (NH4H2PO4) and calcium salts. Calcium nitrate (Ca (NO3)2) and calcium acetate (Ca (CH3COO)2) were used as the calcium sources to clarify the pH dependence of the morphology. We mixed the solutions with the same pH values and agitated them, and observed the products by scanning electron microscopy (SEM) and X-ray diffraction (XRD); the DCPD morphology varies from petal-like to parallelogram structures depending on the initial pH value of the solution and the combination of the starting mixture. The effect of the acetic acid anion is to increase the driving force for the generation of DCPD crystal nuclei.

DCPD, dicalcium phosphate dihydrate (CaHPO 4 •2H 2 O) reacts with fluoride ion in an aqueous solution, and forms fluorapatite (FAp, Ca 10 (PO 4 )6F 2 ). In previous study, we have found that DCPD does not react with fluoride ion directly, but show few hours of induction period by reaction with fluoride. In this study, effect of hydroxyapatite (HA, Ca 10 (PO 4 ) 6 (OH) 2 ) on the reactivity of DCPD with fluoride ion was investigated. By mixing HA with DCPD, it was appeared that the induction period of the reaction was shortened. Morphology of the obtained FAp was similar to HA paricles. We carried on coating of HA on the DCPD particle by soaking DCPD in simulated body fluid (SBF, Kokubo Solution). By coating HA on DCPD particles, particle morphology of the obtained FAp was consistency to the DCPD particles. These results suggest that the shape and particle size of FAp after reaction of DCPD is controllable by DCPD particle as template, and coating with HA. Effect of Hydroxyapatite on

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