Phase transition of amorphous calcium phosphate to calcium hydrogen phosphate dihydrate in simulated body fluid

Abstract We study the initial process of the rapid Ca-P crystallization in SBF by ex situ and in situ observation. To reduce the crystallization rate, calcite are present in the system. Ex situ measurements revealed that amorphous calcium phosphate (ACP) immediately precipitated on SiO2 substrate. The inside of transformed to the calcium hydrogen phosphate. In situ observation indicated that the formation of the DCPD started at day 7 and the DCPD region gradually increased inside ACP particles. Our results showed a solid-solid phase transition from ACP to DCPD. We propose the new pathway of Ca-P crystallization.