Novel core-shell nanocomposites based on TiO2 -covered magnetic Co3 O4 for biomedical applications.

Magnetic Co3 O4 nanoparticles (NPs) have great potential for applications in biomedicine, as contrast enhancement agents for magnetic resonance imaging, or for drug delivery. Although these NPs are so attractive, their potential toxicity raises serious questions about decreasing cellular viability. In this context, Co3 O4 NPs were prepared via sol-gel method and encapsulated with a layer of TiO2 , a biocompatible oxide, and subjected to structural, magnetic and toxicity characterization. X-ray diffractograms of the samples demonstrate the successful synthesis of the spinel and Raman spectroscopy confirms the coating of the Co3 O4 spinel with TiO2 . The Co3 O4 cores showed a very intense superparamagnetic character; however, this behavior is strongly suppressed when the material is covered with TiO2 . According to the neutral red uptake assay, the coating of the cores with TiO2 significantly decreases the cytotoxic character of the Co3 O4 particles and, as it can be observed with the zeta (ξ) potential measurements, they form a stable colloidal dispersion at cytoplasmic pH. The effect of the thermal treatment enhances the biocompatibility even further, with no statistically significant effect on cell viability even at the highest analyzed concentration. The proposed pathway presents a successful sol-gel method for the preparation of Co3 O4 @TiO2 core-shell nanoparticles. This work opens up possibilities for future application of these materials not only for magnetic resonance imaging but also in catalysis and hyperthermia.

Evaluation of in vitro cytotoxicity of superparamagnetic poly(thioether-ester) nanoparticles on erythrocytes, non-tumor (NIH3T3), tumor (HeLa) cells and hyperthermia studies.

Magnetic nanoparticles encapsulated in biocompatible and biodegradable polymeric matrices are promising materials for biomedical applications, such as transport of antitumoral drugs and cancer treatment by hyperthermia. In this study, biobased poly(thioether-ester), PTEe, was obtained by thiol-ene polymerization and superparamagnetic nanoparticles, MNPs, were successfully incorporated in PTEe nanoparticles by miniemulsification followed by solvent evaporation. MNPs-PTEe nanoparticles with average diameter around 150 nm presented superparamagnetic behavior as confirmed by magnetization curves analysis. MNPs-PTEe nanoparticles did not present hemolytic damage on human red blood cells when incubated for 24 h. According to the cell viability assays, nanoparticles did not present any cytotoxic effect on murine fibroblast cell (NIH3T3) and human cervical cancer (HeLa). Hyperthermia assays were applied, demonstrating that AC magnetic field application (110 KHz-500 Oe) for 20 min significantly reduced the cells viability. The morphology evaluation of HeLa showed a hypoxia region one hour after hyperthermia application. Therefore, the results indicated that the superparamagnetic poly(thioether-ester) nanoparticles can be an excellent alternative for the targeted delivery of antitumor drugs and cancer treatment for hyperthermia.

Simultaneous encapsulation of magnetic nanoparticles and zinc phthalocyanine in poly(methyl methacrylate) nanoparticles by miniemulsion polymerization and in vitro studies.

The aim of this work was the simultaneous encapsulation of magnetic nanoparticles (MNPs) and zinc(II) phthalocyanine (ZnPc) in poly(methyl methacrylate) (PMMA) (MNPsZnPc-PMMA) nanoparticles (NPs) by miniemulsion polymerization and to evaluate the photobiological activity and/or hyperthermia (HPT) against human glioblastoma cells (U87MG). MNPsZnPc-PMMA NPs presented an average diameter of 104 ± 2.5 nm with a polydispersity index (PdI) of 0.14 ± 0.03 and negative surface charge - 47 ± 2.2 mV (pH 7.4 ± 0.1). The encapsulation efficiency (EE%) of ZnPc was 85.7% ± 1.30. The release of ZnPc from PMMA NPs was slow and sustained without the presence of burst effect, indicating a homogeneous distribution of the drug in the polymeric matrix. In the biological assay, MNPsZnPc-PMMA NPs showed considerable cytotoxic effect on U87MG cells only after activation with visible light at 675 nm (photodynamic therapy, PDT) or after application of an alternating magnetic field. The simultaneous encapsulation of MNPs and ZnPc in a drug delivery system with sustained release can be a new alternative for cancer treatment leading to significant tumor regression after minimum doses of heat dissipation and light.

Universal properties of magnetization dynamics in polycrystalline ferromagnetic films.

We investigate the scaling behavior in the statistical properties of Barkhausen noise in ferromagnetic films. We apply the statistical treatment usually employed for bulk materials in experimental Barkhausen noise time series measured with the traditional inductive technique in polycrystalline ferromagnetic films having different thickness from 100 to 1000 nm and determine the scaling exponents. Based on this procedure, we group the samples in a single universality class, since the scaling behavior of Barkhausen avalanches is characterized by exponents τ∼1.5, α∼2.0, and 1/σνz∼ϑ∼2.0 for all the films. We interpret these results in terms of theoretical models and provide experimental evidence that a well-known mean-field model for the dynamics of a ferromagnetic domain wall in three-dimensional ferromagnets can be extended for films. We identify that the films present an universal three-dimensional magnetization dynamics, governed by long-range dipolar interactions, even at the smallest thicknesses, indicating that the two-dimensional magnetic behavior commonly verified for films cannot be generalized for all thickness ranges.