Formation of Amorphous Iron‐Calcium Phosphate with High Stability

Abstract

Amorphous iron‐calcium phosphate (Fe‐ACP) plays a vital role in the mechanical properties of teeth of some rodents, which are very hard, but its formation process and synthetic route remain unknown. Here, the synthesis and characterization of an iron‐bearing amorphous calcium phosphate in the presence of ammonium iron citrate (AIC) are reported. The iron is distributed homogeneously on the nanometer scale in the resulting particles. The prepared Fe‐ACP particles can be highly stable in aqueous media, including water, simulated body fluid, and acetate buffer solution (pH 4). In vitro study demonstrates that these particles have good biocompatibility and osteogenic properties. Subsequently, Spark Plasma Sintering (SPS) is utilized to consolidate the initial Fe‐ACP powders. The results show that the hardness of the ceramics increases with the increase of iron content, but an excess of iron leads to a rapid decline in hardness. Calcium iron phosphate ceramics with a hardness of 4 GPa can be achieved, which is higher than that of human enamel. Furthermore, the ceramics composed of iron‐calcium phosphates show enhanced acid resistance. This study provides a novel route to prepare Fe‐ACP, and presents the potential role of Fe‐ACP in biomineralization and as starting material to fabricate acid‐resistant high‐performance bioceramics.

Time-Dependent Effect of Additives on Crystallization of Amorphous Calcium Phosphate: Faster Nucleation after Dilution

“…Generally, ACP particles form immediately in the high-concentration solution (e.g., a calcium ion = a phosphate = 2 mM) . The particles remain stable for less than 1 min to more than a month before completely transforming into HAp within a day. − A pH meter is often used to measure the crystallization kinetics of ACP, but its reliability is rarely discussed . To deal with this problem, we characterized the turbidity, pH, ion concentration (Figure S6), and precipitation structure, as well as calculated the measurement error.…”