Introduction:
For many years, one of the central challenges in nanomedicine has been the design of delivery systems capable of selectively releasing therapeutic agents into target cells. Recently, increasing attention has been directed toward nanostructures that can also function as efficient diagnostic platforms. Magnetite-based magnetic nanoparticles (MNPs) are of particular interest due to their high biocompatibility, surface modification versatility, and controlled navigation under external magnetic fields, all making them promising candidates for the development of theranostic agents. In contrast to conventional biopolymeric and inorganic matrix-based delivery systems, MNPs are able to exhibit magnetomechanical effects when exposed to alternating magnetic fields, which enables their consideration not only as drug carriers but also as autonomous therapeutic agents. The aim of this study was to investigate the effects of magnetic nanoparticles coated with hydrophilic low-molecular-weight ligands on eukaryotic cell lines in the presence of a low-frequency magnetic field.

Methods:
In this work, reproducible synthesis of MNPs was achieved by thermal decomposition of iron pentacarbonyl. TEM analysis revealed an average particle diameter, while XRD confirmed the magnetite structure. Magnetic properties of synthesized MNPs were investigated by VSM. Hydrophobic nanoparticles were further functionalized with hydrophilic ligands such as dopamine (DOPA), folic acid (B9) and 3,4-dihydroxyphenyl acetic acid (DOPAC). Size of nanoparticles transferred into aqueous medium were characterized by DLS. The presence of ligands on the nanoparticle surface was confirmed by IR spectroscopy. Cytotoxicity and the intracellular iron content in cell lysates were also evaluated both with and without exposure to a low-frequency alternating magnetic field.

Results:
Spherical magnetite MNP with an average diameter of 8.2 ± 1.6 nm were synthesized. The crystal lattice parameters (8.373 ± 0.002 Å) and the diffraction pattern obtained by XRD corresponded to a partially oxidized magnetite structure. The CSR calculated from the diffraction pattern was 9.2 ± 0.1 nm, which coincides with the TEM results. Analysis of magnetostatic properties showed the production of superparamagnetic MNP with partial preservation of interactions between crystallites. Hydrophilized MNP with DOPA, DOPAC and B9 ligands were obtained. The average hydrodynamic size of the MNP-ligand determined by the DLS method was about 100 to 400 nm depending on ligands. A series of experiments were carried out on eukaryotic cell lines to study the behavior of MNPs in the presence/absence of low-frequency magnetic field (LFMF). In the absence of LFMF, MNP-DOPA-B9 demonstrated lower cytotoxicity towards the MCF-7 cell line compared to that towards the HEK293 (up to 50%) line as was determined spectrophotometrically (Spectramax). After incubation of MNP-ligand with MCF-7 in low-frequency PVMP, a temporary increase in viability was observed with MNP-DOPAC and MNP-DOPA-B9, exhibiting distinctive biological response to magnetic field effect.

Conclusions:
Thus, hydrophilized MNPs were obtained and characterized. It was demonstrated that magnetic nanoparticles are capable of enhancing cell viability following exposure to a low-frequency magnetic field. The obtained result highlights the potential of MNPs for applications in regenerative medicine.