posted on 2023-09-19, 04:13authored byHaoyue Song, Meng Cai, Zhengyi Fu, Zhaoyong Zou
Amorphous calcium phosphate (ACP) has been widely reported
as a
metastable precursor during the mineralization of calcium phosphates
in bone and enamel. Although the influence of fluoride on the crystallization
of hydroxyapatite (HAP) has been extensively investigated, the mineralization
pathways of ACP in the presence of fluoride are not fully understood.
Here, using a combination of in situ monitoring and ex situ characterizations, we show that fluoride exhibits
little effect on the formation and particle size of ACP nanospheres
from a supersaturated calcium phosphate solution. However, the stability
of ACP increases with increasing concentration of free fluoride ions
in solution. We show that the aggregation of ACP nanospheres into
larger spheres is an important step during ACP crystallization, which
drives the nucleation of plate-like nanocrystals on the surface of
ACP nanospheres and induces subsequent crystallization of ACP via
a dissolution-recrystallization pathway. In the presence of fluoride,
the aggregation of ACP nanospheres and the nucleation of crystalline
phases are retarded, thus stabilizing the amorphous phase. In addition,
fluoride promotes the formation rod-like crystals on the surface of
ACP nanospheres, which grow both outward from solution ions and inward
from ACP nanospheres. These results significantly improve our understanding
of the mineralization pathways of ACP and explain the inhibitory effect
of fluoride during ACP crystallization.