Effect of the aggregation state of amorphous calcium phosphate on hydroxyapatite nucleation kinetics

Calcium phosphates are one of the most important biogenic minerals found in living organisms. Recent studies have suggested a non-classical mineralization pathway, which emphasizes the amorphous calcium phosphate (ACP) as a precursor phase during biomineral crystallization. However, its precise mechanism in mineralization is still poorly understood. Here, we found the aggregation state of ACP affected the nucleation of hydroxyapatite (HAP), which was controlled by collagen-I fibrils in simulated body fluids (SBFs). Our experiment reveals that at low supersaturation, collagen-I fibrils can prevent the self-aggregation of ACP precursor nanoparticles, thus promoting HAP heterogeneous nucleation by increasing the effective surface area of ACP. However, at high supersaturation, the aggregation state of ACP didn't change, and the nucleation rate of HAP kept almost the same. This finding suggests that the aggregation of ACP plays an important role in controlling HAP nucleation kinetics, which follows a new strategy to promote the biomineralization process.