Multifunctional Anisotropic Rod-Shaped CoFe₂O₄ Nanoparticles for Magnetic Resonance Imaging and Magnetomechanical Therapy

Abstract

One-dimensional magnetic nanomaterials, such as nanorods, are one of the most interesting but unexplored objects due to the complexity of their manufacture. In this work, we report on the template-assisted preparation of rod-shaped cobalt ferrite (CoFe 2 O 4 ) nanoparticles (NPs) using the akaganeite (β-FeOOH) matrix and their application as multifunctional agents in biomedicine. In the beginning, rod-shaped β-FeOOH NPs are prepared by a forced hydrolysis technique. Then, amorphous Co(OH) 2 is deposited onto the surface of β-FeOOH. Finally, a solid-state reaction results in mesoporous rodshaped (130 nm × 40 nm) CoFe 2 O 4 NPs with a crystallite size of 7 nm. The proposed mechanism of synthesis involves the simultaneous transformation of β-FeOOH and amorphous Co(OH) 2 in two corresponding oxides during annealing, resulting in cation interdiffusion with the formation of a CoFe 2 O 4 phase, while the key role of the Co(OH) 2 shell in preserving the rod-shaped morphology of CoFe 2 O 4 NPs is demonstrated. NPs exhibit a high coercivity of 73 kA m −1 arising from their shape anisotropy, while their effective anisotropy constant of 1.1 × 10 5 J m −3 is compared to bulk CoFe 2 O 4 . Despite the low value of saturation magnetization (13 A m 2 kg −1 ), NPs demonstrate dual-modal relaxivity in MRI experiments with high values of r 1 = 2.3 s −1 mM −1 and r 2 = 228 s −1 mM −1 . Finally, we show that the magnetomechanical stimulus from NPs leads to the programmed death of breast cancer cells. Under the action of a low-frequency magnetic field (31 Hz), such NPs mediate mechanical vibrations, leading to cancer cell destruction even at a very low concentration of 6 μg CoFe 2 O 4 •mL −1 .

Low-Frequency Dynamic Magnetic Fields Decrease Cellular Uptake of Magnetic Nanoparticles

“…The rate of the nanoparticles' interaction with the cells, and subsequent penetration into the cells, is an important detail. In our work, we chose Fe 3 O 4 MNPs with two types of coating: DOPAC-PEG and DOPAC-HSA-PEG, which can be successfully used in magnetomechanical applications [52] and drug delivery systems, respectively [53]. The MNPs were incubated for different periods from 15 to 120 min in dynamic low-frequency magnetic fields.…”