Manganese and zinc ferrite magnetic nanoparticles (MNPs) were successfully synthesized using the polyol method in ethylene glycol and were found to have high saturation magnetization values (90–95 emu/g at 4 K) when formed by ~30-nm crystallites assembled in an ~80-nm multicore structure. Hyperthermia data revealed a sigmoidal dependence of the specific absorption rate (SAR) on the alternating magnetic field (AMF) amplitude, with remarkable saturation SAR values in water of ~1200 W/g_Fe+Mn and ~800 W/g_Fe+Zn for the Mn and Zn ferrites, respectively. The immobilization of the MNPs in a solid matrix reduced the maximum SAR values by ~300 W/g_{Fe+Mn, Zn} for both ferrites. The alignment of the MNPs in a uniform static magnetic field, before their immobilization in a solid matrix, significantly increased their heating performance. Toxicity assays performed in four cell lines revealed a lower toxicity for the Mn ferrites, while in the case of the Zn ferrites, only ~50% of cells were viable upon their incubation for 24 h with 0.2 mg/mL of MNPs. Cellular uptake experiments revealed that both MNPs entered the cells in a time-dependent manner, as they were found initially in endosomes and later in the cytosol. All of the studied cell lines were more sensitive to the ZnFe₂O₄ MNPs.

Silver nanoparticles (AgNPs) have been proven to have potent antibacterial properties, offering an attractive alternative to antibiotics in the treatment of several infections such as otitis media. Concerns have been raised though regarding their toxicity. There are few data regarding the toxic effects of AgNPs in cochlear cells. The aim of our study was to evaluate the effects of AgNPs of four sizes as a function of their size on HEI-OC1 cochlear cells and on HaCaT keratinocytes. The cells were treated with different concentrations of AgNPs. We evaluated silver uptake by atomic absorption spectroscopy and transmission electron microscopy (TEM), cytotoxicity with the alamarBlue test, ROS production with 2′,7′-dichloro-dihydro-fluorescein diacetate, and genotoxicity with the comet assay. Silver intracellular concentration increased proportionally with the incubation time and the size of the NPs. Silver uptake was higher in HEI-OC1 cells compared to HaCaT. While after 4 h exposure, only the 50 nm NPs were observed in both cell lines and only the 5 nm NPs were observed in the HaCaT cells, after 24 h, nanoparticles of all sizes could be visualized in both cell lines. The cells showed signs of distress: vacuolizations, autophagosomes, signs of apoptosis, or cellular debris. AgNPs of all sizes reduced viability proportionally with the concentration, HEI-OC1 cells being more affected. The toxicity of AgNPs decreased with the nanoparticle size, and ROS production was dose and size dependent, mainly in the cochlear cells. Genotoxicity assessed by comet assay revealed a higher level of DNA lesions in HEI-OC1 cells after treatment with small-sized AgNPs. The perspective of using AgNPs in the treatment of otitis media, although very attractive, must be regarded with caution: cochlear cells proved to be more sensitive to the toxic effect of AgNPs compared to other cell lines. Potential treatments must be tailored specifically, choosing NPs with minimum toxicity towards auditory cells.

Iron oxide magnetic nanoparticles (IOMNPs) have been successfully synthesized by means of solvothermal reduction method employing polyethylene glycol (PEG200) as a solvent. The as-synthesized IOMNPs are poly-dispersed, highly crystalline, and exhibit a cubic shape. The size of IOMNPs is strongly dependent on the reaction time and the ration between the amount of magnetic precursor and PEG200 used in the synthesis method. At low magnetic precursor/PEG200 ratio, the cubic IOMNPs coexist with polyhedral IOMNPs. The structure and morphology of the IOMNPs were thoroughly investigated by using a wide range of techniques: TEM, XRD, XPS, FTIR, and RAMAN. XPS analysis showed that the IOMNPs comprise a crystalline magnetite core bearing on the outer surface functional groups from PEG200 and acetate. The presence of physisorbed PEG200 on the IOMNP surface is faintly detected through FT-IR spectroscopy. The surface of IOMNPs undergoes oxidation into maghemite as proven by RAMAN spectroscopy and the occurrence of satellite peaks in the Fe2p XP spectra. The magnetic studies performed on powder show that the blocking temperature (TB) of IOMNPs is around 300 K displaying a coercive field in between 160 and 170 Oe. Below the TB, the field-cooled (FC) curves turn concave and describe a plateau indicating that strong magnetic dipole-dipole interactions are manifested in between IOMNPs. The specific absorption rate (SAR) values increase with decreasing nanoparticle concentrations for the IOMNPs dispersed in water. The SAR dependence on the applied magnetic field, studied up to magnetic field amplitude of 60 kA/m, presents a sigmoid shape with saturation values up to 1700 W/g. By dispersing the IOMNPs in PEG600 (liquid) and PEG1000 (solid), it was found that the SAR values decrease by 50 or 75 %, indicating that the Brownian friction within the solvent was the main contributor to the heating power of IOMNPs.