Magnetic hydroxyapatite coatings with oriented nanorod arrays: hydrothermal synthesis, structure and biocompatibility

Ideal biocoatings for bone implants should be similar to the minerals of natural bones in chemical composition, crystallinity, and crystallographic texture. Herein, magnetic hydroxyapatite (HA) coatings (MHACs) with oriented nanorod arrays have been fabricated by using magnetic bioglass coatings (CaO-SiO₂-P₂O₅-Fe₃O₄, MBGCs) as sacrificial templates. After the hydrothermal reaction for 24 h, the MBGCs are converted to MHACs in a simulated body fluid (SBF) via a dissolution-precipitation reaction. The formed HA nanorods with a preferential (002) orientation are perpendicular to the coating surfaces. The Fe₃O₄ nanoparticles in the coatings improve the nucleation rate of HA, so the elongated HA nanocrystals are retained even after hydrothermal reaction for 3 days. In contrast, if no magnetic nanoparticles are incorporated into the bioglass coatings (BGCs), the HA nanorods turn into blocky HA particles upon increasing the reaction time from 12 h to 24 h. Moreover, the MHACs possess much better hydrophilicity with a contact angle of 10.8° than the HA coatings because of the presence of Fe₃O₄ nanoparticles. The biocompatibility tests have been investigated by using human bone marrow stromal cells (hBMSCs) as cell models. The hBMSCs have better cell adhesion, spreading and proliferation on the MHACs than on the BGCs or MBGCs because of the HA phase, good hydrophilicity and oriented nanorod arrays. The excellent biocompatibility of the MHACs suggests that they have great potential for bone implants.