Philippe Grosseau

Preparation of polycrystalline yttrium iron garnet ceramics

Abstract The production of polycrystalline ceramics from YIG powders, obtained by reacting Y2O3 and Fe2O3 oxides, is a well understood and controlled industrial process. However, methods of production via chemical pathways, such as coprecipitation, possess the advantage that the garnet powder is more reactive and no longer requires prolonged grinding which can affect its purity. In this paper, we will show that the mastering of these two processes enables the production of ceramics possessing good magnetic characteristics for microwave applications.

Quantification of microsized fluorescent particles phagocytosis to a better knowledge of toxicity mechanisms

Background: The use of micro- or nanometric particles is in full expansion for the development of new technologies. These particles may exhibit variable toxicity levels depending on their physicochemical characteristics. We focused our attention on macrophages (MA), the main target cells of the respiratory system responsible for the phagocytosis of the particles. The quantification of the amount of phagocytosed particles seems to be a major element for a better knowledge of toxicity mechanisms. The aim of this study was to develop a quantitative evaluation of uptake using both flow cytometry (FCM) and confocal microscopy to distinguish entirely engulfed fluorescent microsized particles from those just adherent to the cell membrane and to compare these data to in vitro toxicity assessments. Methods: Fluorescent particles of variable and well-characterised sizes and surface coatings were incubated with MA (RAW 264.7 cell line). Analyses were performed using confocal microscopy and FCM. The biological toxicity of the particles was evaluated [lactate dehydrogenase (LDH) release, tumor necrosis factor (TNF)-α, and reactive oxygen species (ROS) production]. Results and conclusion: Confocal imaging allowed visualization of entirely engulfed beads. The amount of phagocytic cells was greater for carboxylate 2-µm beads (49 ± 11%) than for amine 1-µm beads (18 ± 5%). Similarly, side scatter geometric means, reflecting cellular complexity, were 446 ± 7 and 139 ± 12, respectively. These results confirm that the phagocytosis level highly depends on the size and surface chemical groups of the particles. Only TNF-α and global ROS production varied significantly after 24-h incubation. There was no effect on LDH and H2O2 production.

In vitro cellular responses to silicon carbide nanoparticles: impact of physico-chemical features on pro-inflammatory and pro-oxidative effects

Silicon carbide is an extremely hard, wear resistant, and thermally stable material with particular photoluminescence and interesting biocompatibility properties. For this reason, it is largely employed for industrial applications such as ceramics. More recently, nano-sized SiC particles were expected to enlarge their use in several fields such as composite supports, power electronics, biomaterials, etc. However, their large-scaled development is restricted by the potential toxicity of nanoparticles related to their manipulation and inhalation. This study aimed at synthesizing (by laser pyrolysis or sol–gel methods), characterizing physico-chemical properties of six samples of SiC nanopowders, then determining their in vitro biological impact(s). Using a macrophage cell line, toxicity was assessed in terms of cell membrane damage (LDH release), inflammatory effect (TNF-α production), and oxidative stress (reactive oxygen species generation). None of the six samples showed cytotoxicity while remarkable pro-oxidative reactions and inflammatory response were recorded, whose intensity appears related to the physico-chemical features of nano-sized SiC particles. In vitro data clearly showed an impact of the extent of nanoparticle surface area and the nature of crystalline phases (α-SiC vs. β-SiC) on the TNF-α production, a role of surface iron on free radical release, and of the oxidation state of the surface on cellular H2O2 production.

Size of submicrometric and nanometric particles affect cellular uptake and biological activity of macrophages in vitro.

Background: Micrometric and nanometric particles are increasingly used in different fields and may exhibit variable toxicity levels depending on their physicochemical characteristics. The aim of this study was to determine the impact of the size parameter on cellular uptake and biological activity, working with well-characterized fluorescent particles. We focused our attention on macrophages, the main target cells of the respiratory system responsible for the phagocytosis of the particles. Methods: FITC fluorescent silica particles of variable submicronic sizes (850, 500, 250 and 150 nm) but with similar surface coating (COOH) were tailored and physico-chemically characterized. These particles were then incubated with the RAW 264.7 macrophage cell line. After microscopic observations (SEM, TEM, confocal), a quantitative evaluation of the uptake was carried out. Fluorescence detected after a quenching with trypan blue allows us to distinguish and quantify entirely engulfed fluorescent particles from those just adhering to the cell membrane. Finally, these data were compared to the in vitro toxicity assessed in terms of cell damage, inflammation and oxidative stress (evaluated by LDH release, TNF-α and ROS production respectively). Results and conclusion: Particles were well characterized (fluorescence, size distribution, zeta potential, agglomeration and surface groups) and easily visualized after cellular uptake using confocal and electron microscopy. The number of internalized particles was precisely evaluated. Size was found to be an important parameter regarding particles uptake and in vitro toxicity but this latter strongly depends on the particles doses employed.

Elaboration de poudres de yig par coprecipitation

This paper deals with an original method for the preparation of ferrites with the garnet structure by coprecipitation.The different transformations of the coprecipitated hydroxide during heat treatment are studied and reported.YIG crystallization from amorphous oxide is significantly dependent of some parameters.However, pure homogeneous materials can be obtained at low temperature (800–850‡C) for Al substituted YIG Y3AlxFe5−xO12 with 0.5≤x≤1.

In vitro toxicity of carbon nanotubes, nano-graphite and carbon black, similar impacts of acid functionalization.

Carbon nanotubes (CNT) and nano-graphite (NG) are graphene-based nanomaterials which share exceptional physicochemical properties, but whose health impacts are unfortunately still not well understood. On the other hand, carbon black (CB) is a conventional and widely studied material. The comparison of these three carbon-based nanomaterials is thus of great interest to improve our understanding of their toxicity. An acid functionalization was carried out on CNT, NG and CB so that, after a thorough characterization, their impacts on RAW 264.7 macrophages could be compared for a similar surface chemistry (15 to 120 μg·mL(-1) nanomaterials, 90-min to 24-h contact). Functionalized nanomaterials triggered a weak cytotoxicity similar to the pristine nanomaterials. Acid functionalization increased the pro-inflammatory response except for CB which did not trigger any TNF-α production before or after functionalization, and seemed to strongly decrease the oxidative stress. The toxicological impact of acid functionalization appeared thus to follow a similar trend whatever the carbon-based nanomaterial. At equivalent dose expressed in surface and equivalent surface chemistry, the toxicological responses from murine macrophages to NG were higher than for CNT and CB. It seemed to correspond to the hypothesis of a platelet and fiber paradigm.

Adsorption of lactate dehydrogenase enzyme on carbon nanotubes: how to get accurate results about the cytotoxicity of these nanomaterials

Carbon nanotube (CNT) cytotoxicity is frequently investigated using in vitro classical toxicology assays. However, these cellular tests, usually based on the use of colorimetric or fluorimetric dyes, were designed for chemicals and may not be suitable for nanosized materials. Indeed, because of their unique physicochemical properties CNT can interfere with the assays and bias the results. To get accurate data and draw reliable conclusions, these artifacts should be carefully taken into account. The aim of this study was to evaluate qualitatively and quantitatively the interferences occurring between CNT and the commonly used lactate dehydrogenase (LDH) assay. Experiments under cell-free conditions were performed, and it was clearly demonstrated that artifacts occurred. They were due to the intrinsic absorbance of CNT on one hand and the adsorption of LDH at the CNT surface on the other hand. The adsorption of LDH on CNT was modeled and was found to fit the Langmuir model. The K(ads) and n(eq) constants were defined, allowing the correction of results obtained from cellular experiments to get more accurate data and lead to proper conclusions on the cytotoxicity of CNT.

New insight into artifactual phenomena during in vitro toxicity assessment of engineered nanoparticles: study of TNF-α adsorption on alumina oxide nanoparticle.

Biomolecules can be adsorbed on nanoparticles (NPs) and degraded during in vitro toxicity assays. These artifactual phenomena could lead to misinterpretation of biological activity, such as false-negative results. To avoid possible underestimation of cytokine release after contact between NP and cells, we propose a methodology to account for these artifactual phenomena and lead to accurate measurements. We focused on the pro-inflammatory cytokine tumor necrosis factor TNF-α. We studied well-characterized boehmite engineered NP [aluminum oxide hydroxide, AlO(OH)]. The rate of TNF-α degradation and its adsorption (on boehmite and on the walls of wells) were determined in cell-free conditions by adding a known TNF-α concentration (1500 pg/ml) under various experimental conditions. After a 24-h incubation, we quantified that 7 wt.% of the initial TNF-α was degraded over time, 6 wt.% adsorbed on the walls of 96-well plates, and 13 wt.% adsorbed on the boehmite surface. Finally, boehmite NP were incubated with murine macrophages (RAW 264.7 cell line). The release of TNF-α was assessed for boehmite NP and the experimental data were corrected considering the artifactual phenomena, which accounted for about 20-30% of the total.

In vitro cellular responses to silicon carbide particles manufactured through the Acheson process: Impact of physico-chemical features on pro-inflammatory and pro-oxidative effects

Silicon carbide (SiC) an industrial-scale product manufactured through the Acheson process, is largely employed in various applications. Its toxicity has been poorly investigated. Our study aims at characterizing the physico-chemical features and the in vitro impact on biological activity of five manufactured SiC powders: two coarse powders (SiC C1/C2), two fine powders (SiC F1/F2) and a powder rich in iron impurities (SiC I). RAW 264.7 macrophages were exposed to the different SiC particles and the cellular responses were evaluated. Contrary to what happens with silica, no SiC cytotoxicity was observed but pro-oxidative and pro-inflammatory responses of variable intensity were evidenced. Oxidative stress (H₂O₂ production) appeared related to SiC particle size, while iron level regulated pro-inflammatory response (TNFα production). To investigate the impact of surface reactivity on the biological responses, coarse SiC C1 and fine SiC F1 powders were submitted to different thermal treatments (650-1400 °C) in order to alter the oxidation state of the particle surface. At 1400 °C a decrease in TNFα production and an increase in HO·, COO(·-) radicals production were observed in correlation with the formation of a surface layer of crystalline silica. Finally, a strong correlation was observed between surface oxidation state and in vitro toxicity.

Thermoluminescence of aluminium nitride : Influence of the thermal treatment

Aluminium nitride powders are very sensitive to oxidation: nitrogen atoms are easily substituted by oxygen atoms in the hexagonal structure. Thermoluminescence (TL), in detecting defects in the matter can be used to study oxygen impurities in the AlN lattice. So we tested two powders with different synthesis processes and thermal treatments in order to observe the influence of the oxygen content on the TL curves. First aluminium nitride synthesised with amines and aluminium halides revealed the relation between the TL signal and crystallite size: the TL intensity increased despite the removal of oxide phases and the decrease of oxygen content. Second, Pyrofine R AlN was treated under oxygen flow for 3 h between 200 ° and 1100 °C. The TL spectrum showed the presence of γ-AlON at low temperature and the area of the TL peak (80 °C) increased with the weight ratio of AlN.