Magnesium Ion-Mediated Regulation of Osteogenesis and Osteoclastogenesis in 2D Culture and 3D Collagen/Nano-Hydroxyapatite Scaffolds for Enhanced Bone Repair

Bone regeneration depends on a delicate balance between osteoblast-driven bone formation and osteoclast-mediated resorption, coordinated by complex biochemical cues. Magnesium (Mg²⁺) is known to modulate these processes. However, despite extensive research, its ability to simultaneously enhance osteogenesis and inhibit osteoclast activity remains unclear. In this study, we first investigated the effect of extracellular Mg²⁺ (0, 5, 10, 25, 50 mM) on osteoblast and osteoclast differentiation in 2D culture to determine whether a single Mg²⁺ dosing regimen can simultaneously promote osteogenesis while inhibiting osteoclast differentiation and maturation. A concentration dependent effect of Mg²⁺ was observed on both cell types, with increasing Mg²⁺ concentrations up to 25 mM significantly reducing osteoclast formation yet concurrently inhibiting osteogenic differentiation. At 50 mM, Mg²⁺ exhibited cytotoxic effects on both cell types. We then leveraged the osteogenic properties of biomimetic collagen/nano-hydroxyapatite (Coll/nHA) scaffolds by incorporating Mg²⁺ into the nHA phase to enable localised, controlled delivery. At a scaffold-loaded equivalent of 25 mM Mg²⁺, we observed enhanced bone matrix deposition alongside reduced osteoclast maturation, indicating a synergistic effect between Mg²⁺ and nHA in promoting osteogenesis. While no optimal synergistic dose was identified in 2D culture, these findings demonstrate that Coll-nHA scaffolds offer a promising strategy for localised Mg²⁺ delivery to enhance osteogenesis and suppress osteoclastogenesis. Importantly, the ease of scaffold modification opens the door to incorporating additional bioactive molecules, further advancing their potential in bone tissue engineering applications and the development of next-generation biomaterials for bone regeneration.