Appropriate regulation of magnesium on hydroxyapatite crystallization in simulated body fluids

Abstract

Amorphous calcium phosphate (ACP), as a precursor phase of hydroxyapatite (HAP, the main inorganic mineral of bone) crystallization in a biological system is well documented. Numerous studies have shown that Mg²⁺ can chemically inhibit the transformation of ACP to HAP. Importantly, the inhibition effect is closely related to the addition time of Mg²⁺ for bone mineralization in vivo. However, Mg²⁺ is also widely used to promote bone growth and regeneration in the biomedical field. So, the regulatory role of Mg²⁺ in HAP crystallization remains elusive. In this study, the detailed effect of Mg²⁺ (especially the adding time) on ACP-mediated HAP crystallization is revealed in simulated body fluids. We reported that adding Mg²⁺ before ACP formation or in ACP stable stage can effectively inhibit HAP crystallization; however, in the near phase transformation stage (ACP is unstable), Mg²⁺ does not affect HAP crystallization. In particular, surface associated Mg²⁺ on ACP (compared to Mg²⁺ incorporation) is more suppressive to HAP crystallization. This results indicates that appropriate regulation of Mg²⁺ adding time is vital for amorphous mediated biomineralization, which sheds new light on HAP crystallization regulation.