Graziella Goglio

Thermoresponsive polymer brush-functionalized magnetic manganite nanoparticles for remotely triggered drug release

A thermoresponsive hybrid system for drug delivery purposes is designed by modifying the surface of silica-coated magnetic lanthanum strontium manganite nanoparticles with block copolymers following a non-covalent approach. Block copolymers containing a short poly(L-lysine) segment and a polyether segment of varying composition are adsorbed through electrostatic interactions between positively charged lysine units and negatively charged SiO− groups at the silica surface, giving rise to mixed polyether brushes with a good control over the chain surface density and thickness of the polymer layer. The thermoresponsiveness of the assemblies is controlled by the ethylene oxide/propylene oxide ratio in the polymer brush and the corresponding LCST of the polyether blocks. Important parameters like the aggregation temperature of the particles can be finely adjusted by modifying this ratio. The polarity of the polymer layer can also be varied to maximize the encapsulation efficiency of a moderately hydrophobic drug like doxorubicin. Drug release experiments are performed by taking advantage of the ac magnetically induced heating properties of the magnetic core to speed up the release of doxorubicin owing to structural changes within the polyether brush.

Manganite perovskite nanoparticles for self-controlled magnetic fluid hyperthermia: about the suitability of an aqueous combustion synthesis route

Unaggregated La0.82Sr0.18MnO3 + δ perovskite nanoparticles with a mean crystallite size of 22 nm were successfully synthesized through an aqueous combustion process (Glycine Nitrate Process, GNP) which takes advantage of exothermic, fast and self-sustaining chemical reactions between metal nitrates and glycine as a suitable organic reducing agent. The influence of G/N molar ratio on the phase purity, crystallite size and manganese valency was screened. Fuel-rich conditions were selected to improve chelation of the cations in acidic pH and ensure an accurate control of the cationic composition. Fast calcination was optimized to enhance crystallinity of the nanoparticles and subsequent milling step was performed to favour their desaggregation. The manganite nanoparticles were thoroughly characterized by X-ray diffraction (XRD), elemental chemical analysis, Mohr salt titration and transmission electron microscopy (TEM). According to a process derived from the Stobers method, they were uniformly coated with a 5 nm thick silica shell, as evidenced by TEM, infrared spectroscopy, ζ potential measurements and dynamic light scattering experiments. Preliminary heating experiments in a ac magnetic field showed these core@shell nanoparticles fulfill the requirements for self-controlled magnetic fluid hyperthermia, considering their size (20–70 nm) and their maximum heating temperature (43 °C) which is controlled by the Curie temperature of the magnetic cores.

Silica encapsulated manganese perovskite nanoparticles for magnetically induced hyperthermia without the risk of overheating

Nanoparticles of manganese perovskite of the composition La(0.75)Sr(0.25)MnO(3) uniformly coated with silica were prepared by encapsulation of the magnetic cores (mean crystallite size 24 nm) using tetraethoxysilane followed by fractionation. The resulting hybrid particles form a stable suspension in an aqueous environment at physiological pH and possess a narrow hydrodynamic size distribution. Both calorimetric heating experiments and direct measurements of hysteresis loops in the alternating field revealed high specific power losses, further enhanced by the encapsulation procedure in the case of the coated particles. The corresponding results are discussed on the basis of complex characterization of the particles and especially detailed magnetic measurements. Moreover, the Curie temperature (335 K) of the selected magnetic cores resolves the risk of local overheating during hyperthermia treatment.

Evidence of non-stoichiometry effects in nanometric manganite perovskites: influence on the magnetic ordering temperature

This work tends to evidence that the significant chemical modifications observed in nanometric manganites are not concentrated at the surface of the particles and play a key role on their magnetic properties, especially for the lowest strontium-doping. La1−xSrxMnO3 solid solution with a 27 nm-average crystallite size was prepared via the Glycine Nitrate Process. The evolutions versus x of the Curie temperature (TC) and saturation magnetization of the nanometric solid solution were interpreted taking into account the Goldschmidt tolerance factor, crystallite size, amount of vacancies and the mixed valency of manganese ions. Two distinct populations were distinguished: (i) for x lower than 0.25, the increase of TC with x could be related to the decreasing amount of cationic vacancies that accommodate the substitution at the A-site of the perovskite framework, simultaneously keeping the content of Mn4+% constant; (ii) for x higher than 0.25, the increase of x led to a decrease of the structural distortion, hence favouring orbital overlap and inducing a TC increase. However, when the amount of Mn4+ exceeded the value of ≈35%, competitive superexchange antiferromagnetic interactions were promoted. As a result, the observed behaviour was a compromise between these two competitive tendencies and led to a quasi-constant TC. For x higher than 0.4, the antiferromagnetic interactions became more important, which induced a TC decrease.

Hexagonal-to-cubic phase transformation in composite thin films induced by FePt nanoparticles located at PS/PEO interfaces.

The organization process of asymmetric poly(styrene-block-ethylene oxide) (PS-b-PEO) copolymer thin films blended with FePt nanoparticles is studied. In a first step, it is shown that FePt nanoparticles stabilized by oleic acid ligands are distributed within the PS matrix phase, whereas the same particles partially covered with short dopamine-terminated-methoxy poly(ethylene oxide) (mPEO-Dopa) are located at PS/PEO interfaces. The swelling of PS domains, induced by FePt_oleic acid nanoparticles during the solvent annealing process, results in formation of a disordered microstructure in comparison to the well-organized hexagonally close-packed (HCP) cylinder phase formed in the neat PS-b-PEO copolymer. The evolution of the microstructure of PS-b-PEO/FePt_mPEO-Dopa composite has been investigated for different solvent annealing treatments. Under high-humidity conditions during the vapor annealing process, the addition of FePt nanoparticles results in formation of spheres in the film split into terraces. The upper and lower terraces are occupied by spheres organized in an unusual square and HCP phases, respectively. Under low-humidity conditions, undulated PEO cylinders oriented parallel to substrate are formed in the presence of FePt nanoparticles. In this case, we observe that most of the nanoparticles accumulate within the core of topological defects, which induces a low nanoparticle concentration at the PS/PEO interfaces and so stabilizes an intermediate undulated cylinder phase.

From core–shell BaTiO3@MgO to nanostructured low dielectric loss ceramics by spark plasma sintering

We report a quite general way to design materials with tailored properties by combining thermolysis and fast sintering approaches. Submicrometric-sized BaTiO3 particles have been directly coated in a continuous nanocrystalline MgO shell through a thermal decomposition process. The electron microscopy study has evidenced a shell composed of randomly oriented MgO nanocrystallites. The final nanostructured composite, made of sub-micrometric MgO and BaTiO3 grains uniformly distributed, is obtained in situ during the SPS process. Such a rearrangement can be explained by the initial core–shell architecture, the weak cohesion of the MgO nanocrystallites and their soft plastic behavior under SPS conditions. The composite effect leads to significant modifications in both the dielectric properties and Curie–Weiss parameters compared to uncoated BaTiO3, especially a decrease and thermal stabilization of both the permittivity and the dielectric losses. We ascribe such changes to the stress generated during SPS through the extended interfaces between the two components.

CARBON NITRIDES : A PROMISING CLASS OF MATERIALS

(Received 14 July 2001; In final form 28 September 2001)Using a thermal decomposition process of an organic precursor (thiosemicarbazide) under an argon flow, a brownorange solid was prepared. Chemical analysis, X-ray diffraction and infrared spectroscopy characterizations revealthe formation of a well-crystallized bidimensional carbon nitride compound with a composition close to C

Hierarchical assembly of magnetic L10-ordered FePt nanoparticles in block copolymer thin films

The self-assembly process and local magnetic properties of asymmetric poly(styrene-block-ethylene oxide) (PS-b-PEO) copolymer thin films blended with L10-ordered FePt nanoparticles are studied. During the solvent annealing process, it is shown that L10-ordered FePt nanoparticles covered with short dopamine-terminated-methoxy poly(ethylene oxide) (mPEO-Dopa) are localized within spherical PEO domains having an inter-domain spacing of about 43.2 nm. The magnetic properties of the nanocomposite thin films were then investigated using magnetic force microscopy (MFM). MFM results reveal that each spot (magnetic signal), resulting from the presence of ferromagnetic NPs (coercive field, Hc ∼ 2000 Oe at 300 K), is fully contained in a PEO sphere leading to readily discernible magnetic nanodomains (bits).

Magnetic Nanoparticles for Magnetic Resonance Imaging and Hyperthermia Applications

Medicine provides an increasing interest for magnetic nanoparticles, thanks not only to the growing control of their chemical and morphological design and colloidal stabilization, but also to the increasing tendency to use magnetic fields in diverse medical areas such as radiology, neurosurgery, or oncology. This contribution focuses on their potential usefulness as contrast agents for magnetic resonance imaging (MRI) and colloidal mediators for magnetic fluid hyperthermia (MFH). A physical background of these nanoparticles magnetism is first considered discussing their behavior either under static magnetic field or an alternating one. The design and preparation of magnetic fluids is then described from the synthesis of nanoparticles up to their colloidal stabilization in physiological media. Requirements with regard to in vivo administration are subsequently presented, i.e., the factors affecting their biocompatibility, their biodistribution, the solutions envisaged for enhancing their half-life in the blood compartment, and the active targeting of tumor cells. Finally, magnetic nanoparticles are considered as contrast agents for MRI and mediators for MFH, highlighting the involved problems and the current and future possibilities for solving them.

Photoluminescence of GaN microcrystallites prepared by a new solvothermal process

GaN microcrystallites have been prepared by a solvothermal process. The influence of the synthesis temperature on the crystallinity of the resulting GaN has been studied on three samples, prepared at 400, 600 and 800°C in the same pressure conditions (150 MPa) and duration (6 h). The resulting powders were characterized by several techniques: X-ray diffraction to evaluate the reaction rate, scanning electron microscopy (SEM) to determine the morphology and size of the microcrystallites and photoluminescence to evaluate the quality of the powders.