Synthesis and cytocompatibility of manganese (II) and iron (III) substituted hydroxyapatite nanoparticles

Manganese (II) and iron (III) substituted hydroxyapatite (HA, Ca ₁₀(PO ₄) ₆(OH) ₂) nanoparticles were synthesized using wet chemical method. All samples were single-phase, non-stoichiometric and B-type carbonated hydroxyapatite. Compared with pure HA, Mn ²⁺ substituted (MnHA) and Fe ³⁺ doped HA (FeHA) did not demonstrate significant structure deviation. Since ion exchange mechanism was applied for the synthesis process, the morphology and particle size were not significantly affected: all samples were elongated spheroids of around 70 nm. The presence of Fe and Mn was confirmed by energy dispersive X-ray spectroscopy (EDX) while the concentrations were quantified by inductively coupled plasma (ICP). Fe ³⁺ ions were more active than Mn ²⁺ ions in replacing Ca ²⁺ ions in HA lattice structure. The magnetic property of HA was modified by substitution with Fe. The Fe5 (Fe _added/Ca _added = 5% by molar ratio) was paramagnetic while pure HA was diamagnetic. Results of extraction assay from cells cultured in extracted medium for 72 h suggested that both MnHA and FeHA were non-cytotoxic to osteoblast cells. Meanwhile, the presence of Fe ³⁺ ions in HA demonstrated significant positive effect on osteoblast cells, where the cell number on Fe5 pellets was twice that of pure HA and MnHA samples.