Linking hopping conductivity to giant dielectric permittivity in oxides

With the promise of electronics breakthrough, giant dielectric permittivity materials are under deep investigations. In most of the oxides where such behavior was observed, charged defects at interfaces are quoted for such giant behavior to occur but the underlying conduction and localization mechanisms are not well known. Comparing macroscopic dielectric relaxation to microscopic dynamics of charged defects resulting from electron paramagnetic resonance investigations we identify the actual charged defects in the case of BaTiO3 ceramics and composites. This link between the thermal activation at these two complementary scales may be extended to the numerous oxides were giant dielectric behavior was found

Stimuli-responsive Magnetic Nanohybrids for Triggered Drug Release and Potential Tumor Treatment via Hyperthermia

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Probing the in vitro mechanism of action of cationic lipid/DNA lipoplexes at a nanometric scale

Cationic lipids are used for delivering nucleic acids (lipoplexes) into cells for both therapeutic and biological applications. A better understanding of the identified key-steps, including endocytosis, endosomal escape and nuclear delivery is required for further developments to improve their efficacy. Here, we developed a labelling protocol using aminated nanoparticles as markers for plasmid DNA to examine the intracellular route of lipoplexes in cell lines using transmission electron microscopy. Morphological changes of lipoplexes, membrane reorganizations and endosomal membrane ruptures were observed allowing the understanding of the lipoplex mechanism until the endosomal escape mediated by cationic lipids. The study carried out on two cationic lipids, bis(guanidinium)-tris(2-aminoethyl)amine-cholesterol (BGTC) and dioleyl succinyl paramomycin (DOSP), showed two pathways of endosomal escape that could explain their different transfection efficiencies. For BGTC, a partial or complete dissociation of DNA from cationic lipids occurred before endosomal escape while for DOSP, lipoplexes remained visible within ruptured vesicles suggesting a more direct pathway for DNA release and endosome escape. In addition, the formation of new multilamellar lipid assemblies was noted, which could result from the interaction between cationic lipids and cellular compounds. These results provide new insights into DNA transfer pathways and possible implications of cationic lipids in lipid metabolism

Synthesis and chemical surface modification of maghemite nanoparticles for biomedical applications.

Ce travail porte sur le développement de nanovecteurs magnétiques à base de nanoparticules, destinés à des applications biomédicales in vivo. Les études se sont dirigées vers l'optimisation du couplage de macromolécules de dextran et de dérivés de polyoxyde d'éthylène à la surface des nanoparticules magnétiques afin de les rendre biocompatibles. Des nanoparticules de maghémite, préalablement synthétisées, ont étémodifiées en surface par des agents de couplage silaniques organofonctionnels suivi du greffage covalent des macromolécules. Les nanovecteurs, ont ensuite été marqués par des sondes fluorescentes pour réaliser destests in vitro de double marquage (IRM, fluorescence) de microglies humaines (HEMC5).This work deals with the development of nanovectors containing superparamagnetic nanoparticles, intended for in vivo biomedical applications. The studies moved towards the optimization of the macromolecule coupling such as dextran and polyethyleneoxide derivativeson the surface of magnetic nanoparticles in order to make them biocompatible. Surfaces of previously synthesized maghemite nanoparticles were modified by organofunctional silane coupling agents followed by a covalent grafting of the macromolecules. The nanovectors were then labeled by fluorescent probes to carry out double labeling in vitro tests (IRM, fluorescence) on human microglies (HEMC5)

Synthèse et modification chimique de la surface de nanoparticules de maghémite à des fins d'applications biomédicales

Ce travail porte sur le développement de nanovecteurs magnétiques à base de nanoparticules, destinés à des applications biomédicales in vivo. Les études se sont dirigées vers l'optimisation du couplage de macromolécules de dextran et de dérivés de polyoxyde d'éthylène à la surface des nanoparticules magnétiques afin de les rendre biocompatibles. Des nanoparticules de maghémite, préalablement synthétisées, ont été modifiées en surface par des agents de couplage silaniques organofonctionnels suivi du greffage covalent des macromolécules. Les nanovecteurs, ont ensuite été marqués par des sondes fluorescentes pour réaliser des tests in vitro de double marquage (IRM, fluorescence) de microglies humaines (HEMC5).This work deals with the development of nanovectors containing superparamagnetic nanoparticles, intended for in vivo biomedical applications. The studies moved towards the optimization of the macromolecule coupling such as dextran and polyethyleneoxide derivatives on the surface of magnetic nanoparticles in order to make them biocompatible. Surfaces of previously synthesized maghemite nanoparticles were modified by organofunctional silane coupling agents followed by a covalent grafting of the macromolecules. The nanovectors were then labeled by fluorescent probes to carry out double labeling in vitro tests (IRM, fluorescence) on human microglies (HEMC5)