Calcium phosphate-forming ability of magnetite and related materials in a solution mimicking in vivo conditions

•Behavior of iron-based materials in simulated body fluid (SBF) was investigated.•Magnetite and hematite induced calcium phosphate formation in SBF.•Wustite, maghemite, and goethite did not induce calcium phosphate formation in SBF.•Specific FeOH groups on particle surface possibly induced calcium phosphate formation in SBF.

Iron-based compounds, especially magnetite (Fe3O4), can be a candidate of thermoseeds for hyperthermia therapy. When iron-based compounds are applied for bone tumor treatment, they should have a heat-generating property and a bone-bonding property. However, the bone-bonding property of iron-based compounds is still unclear. The bone-bonding property of materials is estimated by their bone-like apatite formation property in simulated body fluid (SBF). The method to estimate apatite forming ability of materials by utilizing SBF was introduced by Kokubo et al. We thus report fundamental research into the behavior of iron oxides and an iron oxyhydroxide namely: FeO, Fe3O4, α-Fe2O3, γ-Fe2O3, and α-FeOOH, in SBF. Calcium phosphate precipitation was found in Fe3O4 and α-Fe2O3 within 7 and 28 days after soaking in SBF, respectively, while FeO, γ-Fe2O3, and α-FeOOH did not. Our results indicate that Fe3O4 and α-Fe2O3 have a better potential bone-bonding property than FeO, γ-Fe2O3, and α-FeOOH. The induction of apatite precipitation in SBF can be attributed to the specific structure of FeOH groups on the surface of Fe3O4 and α-Fe2O3.