Synthesis and characterization of mesoporous and hollow-mesoporous MxFe3-xO4 (M=Mg, Mn, Fe, Co, Ni, Cu, Zn) microspheres for microwave-triggered controllable drug delivery

Spinel ferrites can be used in magnetic targeting and microwave heating and can therefore be used for targeted and controllable drug delivery. We used the cetyltrimethylammonium bromide-assisted solvothermal method to synthesize a series of spinel ferrites (MxFe3-xO4, M= Mg, Mn, Fe, Co, Ni, Cu, Zn) with a mesoporous or hollow-mesoporous structure suitable for direct drug loading and the particle diameters ranging from 200 to 350 nm. We investigated the effects of M2+ cation on the morphology and properties of these products by analyzing their transmission electron microscopy images, mesoporous properties, magnetic properties, and microwave responses. We chose hollow-mesoporous MxFe3-xO4 (M= Fe, Co, Zn) nanoparticles, which had better overall properties, for the drug VP16 (etoposide) loading and microwavecontrolled release. The CoxFe3-xO4 and Fe3O4 particles trapped 61.5 and 64.8%, respectively, of the VP16, which were higher than that (60.4%) of ZnxFe3-xO4. Controllable drug release by these simple magnetic nanocarriers can be achieved by microwave irradiation, and VP16-loaded CoxFe3-xO4 released the most VP16 molecules (more than 50% after 1 h and 69.1% after 6 h) under microwave irradiation. Our results confirm the favorable drug loading and microwave-controlled delivery by these ferrites, and lay a theoretical foundation to promote clinical application of the targeted controllable drug delivery system. In the present study, we prepared mesoporous or hollow-mesoporous spinel ferrites (MxFe3-xO4, M= Mg, Mn, Fe, Co, Ni, Cu, Zn) by CTAB-assisted solvothermal method and solved the problem of Cu and Ni impurities in CuxFe3-xO4 and NixFe3-xO4 products by means of magnetic separation and additional redox reactions, respectively. We investigated the effects of the M2+ cation on the morphology, mesoporous properties, magnetic properties, and microwave responses of these ferrites. Then, the drug loading and microwave-controlled drug release of hollow-mesoporous MxFe3-xO4 (M = Fe, Co, Zn) nanoparticles with better overall properties were also studied. CoxFe3-xO4 has the best overall performances for microwave-controlled drug release.