Christine Labrugère

Sonochemical Approach to the Synthesis of Fe3O4@SiO2 Core−Shell Nanoparticles with Tunable Properties

In this study, we report a rapid sonochemical synthesis of monodisperse nonaggregated Fe(3)O(4)@SiO(2) magnetic nanoparticles (NPs). We found that coprecipitation of Fe(II) and Fe(III) in aqueous solutions under the effect of power ultrasound yields smaller Fe(3)O(4) NPs with a narrow size distribution (4-8 nm) compared to the silent reaction. Moreover, the coating of Fe(3)O(4) NPs with silica using an alkaline hydrolysis of tetraethyl orthosilicate in ethanol-water mixture is accelerated many-fold in the presence of a 20 kHz ultrasonic field. The thickness of the silica shell can be easily controlled in the range of several nanometers during sonication. Mossbauer spectra revealed that nonsuperparamagnetic behavior of obtained core-shell NPs is mostly related to the dipole-dipole interactions of magnetic cores and not to the particle size effect. Core-shell Fe(3)O(4)@SiO(2) NPs prepared with sonochemistry exhibit a higher magnetization value than that for NPs obtained under silent conditions owing to better control of the deposited silica quantities as well as to the high speed of sonochemical coating, which prevents the magnetite from oxidizing.

The effect of RGD density on osteoblast and endothelial cell behavior on RGD-grafted polyethylene terephthalate surfaces

Hybrid materials combining polyethylene terephthalate and different types of cells (endothelial and osteoblastic cells) have been developed thanks to the covalent grafting of different densities of RGD containing peptides onto the polymer surface. Biomimetic modifications were performed by means of a three-step reaction procedure: creation of COOH functions, coupling agent grafting and the immobilization of the RGDC peptides. High resolution mu-imager was used to evaluate RGD densities (varying between 0.6 and 2.4 pmol/mm(2)) and has exhibited the stability of the surface grafted peptides when treated in harsh conditions. The efficiency of this route for biomimetic modification of a PET surface was demonstrated by measuring the adhesion of MC3T3 and HSVEC cells and by focal adhesion observation. Results obtained prove that a minimal RGDC density of 1 pmol/mm(2) is required to improve MC3T3 and HSVEC cells responses. Indeed, cells seeded onto a RGDC-modified PET with a density higher than 1 pmol/mm(2) were able to establish focal adhesion as visualized by fluorescence microscope compared to cells immobilized onto unmodified PET and RGDC-modified PET with densities lower than 1 pmol/mm(2). Moreover, the number of focal contacts was enhanced by the increase of RGDC peptide densities grafted onto the material surface. With this study we proved that the density of peptides immobilized on the surface is a very important parameter influencing osteoblast or endothelial cell adhesion and focal contact formation.

LPCVD and characterization of boron-containing pyrocarbon materials

Pyrocarbon materials containing various amounts of boron have been prepared by LPCVD from BC13C3H8H2 precursor mixtures. By increasing the BCl3(C3H8 + BCl3) ratio up to 85%, the incorporation of boron can reach 33 at.%. A small amount of boron (e.g. 8 at.%) highly enhances the structural anisotropy of pyrocarbon, as evidenced by optical microscopy, X-ray diffraction and transmission electron microscopy (selected area diffraction and lattice fringes techniques). X-ray photoelectron spectroscopy has shown that a large fraction of the boron atoms are included by substitution in the carbon layers; the remaining boron atoms belong to a boron-rich amorphous part of the material. As the boron content increases beyond 8 at.%, the structural anisotropy of the boron-rich pyrocarbon decreases, due to the limited growth and stacking of the carbon layers. Also, amorphous boron-rich regions are more and more abundant as the total amount of boron increases. The oxidation resistance of the C(B) materials is better than that of pure pyrocarbon. This is mainly due to the improvement of the structural organization for the low boron content materials and to the coating of the whole material with a stable boron oxide for materials with a higher boron content.

Tribological behaviour of hard coatings deposited by arc-evaporation PVD

Hard coatings deposited by arc-evaporation PVD are adequate solutions for increasing the lifetime of tools and components commonly employed in many different industrial applications. The present paper reports a comparative study of the tribological properties of the most employed hard coatings like TiN, TiCN, TiAlN, CrN and ZrN. In this study, microhardness tests were carried out by using a microindenter. Friction and wear tests were carried out by using a ball-on-disk tribometer and an optical profilometer. AUGER and XPS techniques were employed to measure the stoichiometry and thickness of the different films.

Characterization of nearly stoichiometric SiC ceramic fibres

A comparative study of the chemical composition and microstructure of Hi-Nicalon, Hi-Nicalon type S, Tyranno SA, Sylramic and Carborundum fibres has been conducted. This analysis has confirmed results already published but has also evidenced some original features. The Hi-Nicalon type S fibre has a near stoichiometric composition but it still contains some oxygen (≈1 at. %) and free carbon (≈2 at. %). The expected near stoichiometric composition of both the Tyranno SA and the Sylramic fibres is only effective near the edge region, while the core of the fibres contains some amount of free carbon (e.g., up to ≈14 at. % and ≈6 at. % respectively in large diameter fibres) as well as some residual oxygen (≈0.5 at. %). The composition of the Carborundum fibre is very close to stoichiometric SiC except rare and localised free carbon or B4C inclusions. The properties of the different fibres, some of them still beeing at a development stage, are discussed from a chemical and a phase composition point of view, on the basis of what is known about their respective preparation process.

Influence of nanohelical shape and periodicity on stem cell fate.

Microenvironments such as protein composition, physical features, geometry, and elasticity play important roles in stem cell lineage specification. The components of the extracellular matrix are known to subsequently assemble into fibrillar networks in vivo with defined periodicity. However, the effect of the most critical parameter, which involves the periodicity of these fibrillar networks, on the stem cell fate is not yet investigated. Here, we show the effect of synthetic fibrillar networks patterned with nanometric periodicities, using bottom-up approaches, on the response of stem cells. We have used helical organic nanoribbons based on self-assemblies of Gemini-type amphiphiles to access chiral silica nanoribbons with two different shapes and periodicities (twisted ribbons and helical ribbons) from the same native self-assembled organic nanostructure. We demonstrate the covalent grafting of these silica nanoribbons onto activated glass substrates and the influence of this programmed isotropically oriented matrix to direct the commitment of human mesenchymal stem cells (hMSCs) into osteoblast lineage in vitro, free of osteogenic-inducing media. The specific periodicity of 63 nm (±5 nm) with helical ribbon shape induces specific cell adhesion through the fibrillar focal adhesion formation and leads to stem cell commitment into osteoblast lineage. In contrast, the matrix of periodicity 100 nm (±15 nm) with twisted ribbon shape does not lead to osteoblast commitment. The inhibition of non-muscle myosin II with blebbistatin is sufficient to block this osteoblast commitment on helical nanoribbon matrix, demonstrating that stem cells interpret the nanohelical shape and periodicity environment physically. These results indicate that hMSCs could interpret nanohelical shape and periodicity in the same way they sense microenvironment elasticity. This provides a promising tool to promote hMSC osteogenic capacity, which can be exploited in a 3D scaffold for bone tissue engineering.

Rapid Hydrothermal Synthesis of VO2 (B) and Its Conversion to Thermochromic VO2 (M1)

The present study provides a rapid way to obtain VO2 (B) under economical and environmentally friendly conditions. VO2 (B) is one of the well-known polymorphs of vanadium dioxide and is a promising cathode material for aqueous lithium ion batteries. VO2 (B) was successfully synthesized by rapid single-step hydrothermal process using V2O5 and citric acid as precursors. The present study shows that phase-pure VO2 (B) polytype can be easily obtained at 180 °C for 2 h and 220 °C for 1 h, that is, the lowest combination of temperature and duration reported so far. The obtained VO2 (B) is characterized by X-ray powder diffraction, high-resolution scanning electron microscopy, and Fourier transform infrared spectroscopy. In addition, we present an indirect way to obtain VO2 (M1) by annealing VO2 (B) under vacuum for 1 h.

Low-Temperature UV Processing of Nanoporous SnO2 Layers for Dye-Sensitized Solar Cells

Connection of SnO₂ particles by simple UV irradiation in air yielded cassiterite SnO₂ porous films at low temperature. XPS, FTIR, and TGA-MS data revealed that the UV treatment has actually removed most of the organics present in the precursor SnO₂ colloid and gave more hydroxylated materials than calcination at high temperature. As electrodes for dye-sensitized solar cells (DSCs), the N3-modified 1-5 μm thick SnO₂ films showed excellent photovoltaic responses with overall power conversion efficiency reaching 2.27% under AM1.5G illumination (100 mW cm⁻²). These performances outperformed those of similar layers calcined at 450 °C mostly due to higher V(oc) and FF. These findings were rationalized in terms of slower recombination rates for the UV-processed films on the basis of dark current analysis, photovoltage decay, and electrical impedance spectroscopy studies.

Dual Lithium Insertion and Conversion Mechanisms in a Titanium-Based Mixed-Anion Nanocomposite

The electrochemical reaction of lithium with a vacancy-containing titanium hydroxyfluoride was studied. On the basis of pair distribution function analysis, NMR, and X-ray photoelectron spectroscopy, we propose that the material undergoes partitioning upon initial discharge to form a nanostructured composite containing crystalline Li(x)TiO(2), surrounded by a Ti(0) and LiF layer. The Ti(0) is reoxidized upon reversible charging to an amorphous TiF(3) phase via a conversion reaction. The crystalline Li(x)TiO(2) is involved in an insertion reaction. The resulting composite electrode, Ti(0)-LiF/Li(x)TiO(2) ⇔ TiF(3)/ Li(y)TiO(2), allows reaction of more than one Li per Ti, providing a route to higher capacities while improving the energy efficiency compared to pure conversion chemistries.

Poly(acrylic acid)-block-poly(vinyl alcohol) anchored maghemite nanoparticles designed for multi-stimuli triggered drug release

Original core/corona nanoparticles composed of a maghemite core and a stimuli-responsive polymer coating made of poly(acrylic acid)-block-poly(vinyl alcohol) macromolecules were fabricated for drug delivery system (DDS) application. This kind of DDS aims to combine the advantage of stimuli-responsive polymer coating, in order to regulate the drug release behaviours under different conditions and furthermore, improve the biocompatibility and in vivo circulation half-time of the maghemite nanoparticles. Drug loading capacity was evaluated with methylene blue (MB), a cationic model drug. The triggered release of MB was studied under various stimuli such as pH, ionic strength and temperature. Local heating generated under alternating magnetic field (AMF) application was studied, and remotely AMF-triggered release was also confirmed, while a mild heating-up of the release medium was observed. Furthermore, their potential application as magnetic resonance imaging (MRI) contrast agents was explored via relaxivity measurements and acquisition of T2-weighted images. Preliminary studies on the cytotoxicity against mouse fibroblast-like L929 cell line and also their cellular uptake within human melanoma MEL-5 cell line were carried out. In conclusion, this kind of stimuli-responsive nanoparticles appears to be promising carriers for delivering drugs to some tumour sites or into cellular compartments with an acidic environment.