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The craniomaxillofacial region contains several bones and serves to protect and support the area from the brain to the masticatory system. In this paper, the clinical and research aspects of craniomaxillofacial biomaterials are highlighted to serve as a guide into the wide world of their reconstructions. After a quick look into the anatomy, this review focuses on the causes of large bone defects in this region and how they influence the designing process of the implant. Since it is a large area to unfold, only the maxillary, the mandible and the temporomandibular joints are highlighted. Understanding the biomechanics of mandible and temporomandibular joints is quite important, as it strongly influences the choice of the biomaterial. Thus, the latest techniques implemented to understand the biomechanics of the mandible are also highlighted. By way of the finite-element analysis, a simulation can help identify the forces and the movements of the mandible and predict the possible outcome of the implantation influencing the choice of the biomaterial.

The “stress-shielding” problem, common with metallic implants, may be solved by using biocompatible sandwiches with a polymeric core between two metallic skin sheets. To achieve such sandwiches, a process route has been developed, beginning with the grafting of poly-(methyl-methacrylate) (PMMA) on titanium (Ti) sheets via the “grafting from” technique. Grafting resulted in variable thicknesses of PMMA on the Ti sheets. Hot-pressing was used to prepare semi-finished Ti–PMMA–Ti sandwiches. The adhesion was achieved by the interpenetration between PMMA sheet and the grafted PMMA chains. Investigation was carried out to understand the influence of the grafted PMMA thickness on the adhesion strength. Similar adhesion strengths were found for the sandwiches despite variable grafted PMMA thicknesses, indicating a successful grafting of PMMA on large-scale Ti sheets. The adhesion followed the autohesion theory, where a time-dependent increase in adhesion strength was found for the sandwiches.

Materials Chemistry and Physics, 276, ISSN:0254-0584

The world of biomaterials has been continuously evolving. Where in the past only mono-material implants were used, the growth in technology and collaboration between researchers from different sectors has led to a tremendous improvement in implant industry. Nowadays, composite materials are one of the leading research areas for biomedical applications. When we look toward hard tissue applications, metal-based composites seem to be desirable candidates. Metals provide the mechanical and physical properties needed for load-bearing applications, which when merged with beneficial properties of bioceramics/polymers can help in the creation of remarkable bioactive as well biodegradable implants. Keeping this in mind, this review will focus on various production routes of metal-based composite materials for hard tissue applications. Where possible, the pros and cons of the techniques have been provided.

International audience; Titanium (Ti) is the most commonly used material for cranial prostheses. However, this material does not exhibit the same mechanical properties as the bone. Incorporating polymers onto Ti by combining both their properties is a solution to overcome this issue. Thus, sandwich materials made of two Ti skin sheets and a poly(methyl methacrylate) (PMMA) core are promising structures to design biomedical prostheses. The "grafting to" and "grafting from" procedures to functionalize the Ti/PMMA interface are described in this paper as two strategies for chemically connecting PMMA chains on Ti surfaces. The advantage of the first approach is the capacity to control the architecture of the grafted PMMA on Ti. Moreover, a method for selectively grafting a bioactive polymer such as poly(sodium styrene sulfonate) (PNaSS) on one side of the Ti and PMMA on the other side is developed. This contribution presents efficient ways of functionalizing Ti for biomedical applications.

International audience; Embedding nanoparticles (NPs) with organic shells is a way to control their aggregation behavior. Using polymers allows reaching relatively high shell thicknesses but suffers from the difficulty of obtaining regular hybrid objects at gram scale. Here, we describe a three-step synthesis in which multi-gram NP batches are first obtained by thermal decomposition, prior to their covalent grafting by an atom transfer radical polymerization (ATRP) initiator and to the controlled growing of the polymer shell. Specifically, non-aggregated iron oxide NPs with a core principally composed of γ-Fe2O3 (maghemite) and either polystyrene (PS) or polymethyl methacrylate (PMMA) shell were elaborated. The oxide cores of about 13 nm diameter were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). After the polymerization, the overall diameter reached 60 nm, as shown by small-angle neutron scattering (SANS). The behavior in solution as well as rheological properties in the molten state of the polymeric shell resemble those of star polymers. Strategies to further improve the screening of NP cores with the polymer shells are discussed.

The stability of interfaces between polymethyl methacrylate (PMMA) and titanium (Ti) are tested in a Ringer solution that is an aggressive medium usually used for biomaterial evaluation. The devices are PMMA-grafted/Ti elaborated via a “grafting-from” method involving three steps, the alkali activation of Ti sheets, their functionalization with an initiator of polymerization through a phosphonate anchoring group and the growth of PMMA brushes. Electrochemical characterizations demonstrate that the stability of the PMMA-grafted/Ti interface in biological medium is satisfactory and that the grafting of PMMA is even acting as a protective barrier for titanium. Indeed, PMMA-grafted/Ti remains passive in Ringer solution until at least +3 V/SCE (saturated calomel electrode), even under inflammatory conditions, while localized corrosion was measured on as-received titanium in similar conditions. This protecting role is attributed to the grafted interface, since spin-coated PMMA does not decrease the corrosion sensitivity of titanium.

International audience

Physical Review Materials, 3 (12), ISSN:2475-9953

Metal surfaces coated with organic layers are innovative materials with high potential for many industrial applications. To overcome the limitations due to the generally poor adhesion between these two components, polymers covalently anchored onto the substrate (‘grafted’ polymers) have been proposed as adhesives interlayers. Their mechanical properties, however, strongly affect their performances and thus have to be characterized at different scales. In this paper we report the mechanical characterization of thick poly(methyl methacrylate) (PMMA) layers grafted on titanium substrates using standard nanoindentation as well as different AFM-based techniques, namely AFM-based nanoindentation, contact resonance AFM (CR-AFM), HarmoniX™, and PeakForce quantitative nanomechanical mapping (PF-QNM™). The specific results obtained with each technique reflect the mechanical properties at different scales for these multiscale systems. Thus, these methods constitute a unique set of techniques for the complete analysis of the mechanical response of advanced materials from the macro- down to the nanoscale.

We report on the growth and formation of single-layer boron nitride dome-shaped nanostructures mediated by small iron clusters located on flakes of hexagonal boron nitride. The nanostructures were synthesized in situ at high temperature inside a transmission electron microscope while the e-beam was blanked. The formation process, typically originating at defective step-edges on the boron nitride support, was investigated using a combination of transmission electron microscopy, electron energy loss spectroscopy and computational modelling. Computational modelling showed that the domes exhibit a nanotube-like structure with flat circular caps and that their stability was comparable to that of a single boron nitride layer.

Three approaches to preparing iron oxide nanoparticle-decorated microbubbles (NP-decoMBs) have been investigated. The size and stability characteristics of these microbubbles (MBs) were investigated by optical microscopy, laser light scattering and an acoustical method, and compared with those of non-decorated MBs. First, magnetite nanoparticles (Fe3O4NPs) grafted with dimyristoylphosphatidylcholine (DMPC) were synthesized and used to prepare MBs by brief sonication under an atmosphere of air saturated with perfluorohexane. These MBs had a rather large mean radius (r ~ 12 µm), and a moderate volume of encapsulated gas. Remarkably, a second approach that consisted of dispersing unbound DMPC molecules in the aqueous phase along with DMPC-grafted Fe3O4NPs prior to sonication was found to drastically change the situation, allowing the obtaining of monomodal populations of much smaller (r ~ 0.6 µm) NP-decoMBs. The latter were echogenic and stable for at least 10 days at room temperature, without significant variation of their size characteristics. In a third approach, NP-decoMBs were directly prepared from dispersions of naked Fe3O4NPs in the presence of DMPC. The resulting NP-decoMBs suspensions consisted of broadly distributed bubble populations mostly containing two populations (with r ~ 5 and ~ 15 µm). Control microbubbles made of DMPC only were small (r ~ 1.3 µm), although not as small as those formed from DMPC-grafted Fe3O4NPs in the presence of free DMPC, and were less stable, with a room temperature half-life of only ~1 day. These observations imply that there is a synergy between the Fe3O4NPs and the DMPC molecules in the air/water interfacial film stabilization process.

The engineering of iron oxide nanoparticles (IONPs) for biomedical use has received great interest over the past decade. In the present study we investigated the biocompatibility of IONPs grafted with linear (2P) or generation 1 (2PG1) or 2 (2PG2) dendronized oligoethyleneglycol units in THP-1-derived macrophages. To evaluate IONP effects on cell functionality and homeostasis, mitochondrial function (MTT assay), membrane permeability (LDH release), inflammation (IL-8), oxidative stress (reduced glutathione, GSH), NLRP3 inflammasome activation (IL-1β) and nanoparticle cellular uptake (intracellular iron content) were quantified after a 4-h or 24-h cell exposure to increasing IONP concentrations (0–300 µg Fe/mL). IONPs coated with a linear molecule, NP10COP@2P, were highly taken up by cells and induced significant dose-dependent IL-8 release, oxidative stress and NLRP3 inflammasome activation. In comparison, IONPs coated with dendrons of generation 1 (NP10COP@2PG1) and 2 (NP10COP@2PG2) exhibited better biocompatibility. Effect of the dendritic architecture of the surface coating was investigated in a kinetic experiment involving cell short-term exposure (30 min or 1 h 30) to the two dendronized IONPs. NP10COP@2PG2 disrupted cellular homeostasis (LDH release, IL-1β and IL-8 secretion) to a greater extend than NP10COP@2PG1, which makes this last IONP the best candidate as MRI contrast or theranostic agent.

International audience; Titanium (Ti) is the most widely used metal in biomedical applications because of its biocompatibility; however, the significant difference in the mechanical properties between Ti and the surrounding tissues results in stress shielding which is detrimental for load-bearing tissues. In the current study, to attenuate the stress shielding effect, a new processing route was developed. It aimed at growing thick poly(methyl methacrylate) (PMMA) layers grafted on Ti substrates to incorporate a polymer component on Ti implants. However, the currently available methods do not allow the development of thick polymeric layers, reducing significantly their potential uses. The proposed route consists of an alkali activation of Ti substrates followed by a surface-initiated atom transfer radical polymerization using a phosphonic acid derivative as a coupling agent and a polymerization initiator and malononitrile as a polymerization activator. The average thickness of the grown PMMA layers is approximately 1.9 μm. The Ti activation-performed in a NaOH solution-leads to a porous sodium titanate interlayer with a hierarchical structure and an open microporosity. It promotes the covalent grafting reaction because of high hydroxyl groups' content and enables establishing a further mechanical interlocking between the growing PMMA layer and the Ti substrate. As a result, the produced graduated structure possesses high Ti/PMMA adhesion strength (∼260 MPa). Moreover, the PMMA layer is (i) thicker compared to those obtained with the previously reported techniques (∼1.9 μm), (ii) stable in a simulated body fluid solution, and (iii) biocompatible. This strategy opens new opportunities toward hybrid prosthesis with adjustable mechanical properties with respect to host bone properties for personalized medicines.

Objective. The aim of this study was to improve the strength and quality of the titanium-hydroxyapatite interface in order to prevent long-term failure of the implanted devices originating from coating delamination and to test it in an in-vivo model. Methods. Ti disks and dental commercial implants were etched in Kroll solution. Thermochemical treatments of the acid-etched titanium were combined with sol-gel hydroxyapatite (HA) coating processes to obtain a nanoporous hydroxyapatite/sodium titanate bilayer. The sodium titanate layer was created by incorporating sodium ions onto the Ti surface during a NaOH alkaline treatment and stabilized using a heat treatment. HA layer was added by dip-coating in a sol-gel solution. The bioactivity was assessed in vitro with murine MC3T3-E1 and human SaOs-2 cells. Functional and histopathological evaluations of the coated Ti implants were performed at 22, 34 and 60 days of implantation in a dog lower mandible model. Results. Nanoporous hydroxyapatite/sodium titanate bilayer on titanium implants was sensitive neither to crack propagation nor to layer delamination. The in vitro results on murine MC3T3-E1 and human SaOs-2 cells confirm the advantage of this coating regarding the capacity of cell growth and differentiation. Signs of progressive bone incorporation, such as cancellous bone formed in contact with the implant over the existing compact bone, were notable as early as day 22. Overall, osteoconduction and osteointegration mean scores were higher for test implants compared to the controls at 22 and 34 days. Significance. Nanoporous hydroxyapatite/sodium titanate bilayer improves the in-vivo osteoconduction and osteointegration. It prevents the delamination during the screwing and it could increase HA-coated dental implant stability without adhesive failures. The combination of thermochemical treatments with dip coating is a low-cost strategy. (C) 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

We show that water-soluble monosodic salts of F-alkyl phosphates CnF2n+1(CH2)(2)OP(O)(OH)(2), with n = 8 and 10 (F8H2Phos and F10H2Phos) form Gibbs films with exceptionally high dilational viscoelastic modules E that reach similar to 900 mN m(-1) in the condensed phases. These E values are up to one order of magnitude larger than those recorded for phospholipid, protein and polymer films commonly considered as highly viscoelastic. F8H2Phos.1Na undergoes a transition between a liquid-expanded and a liquid-condensed phase. In the case of F10H2Phos.1Na, a transition occurs between a gas phase of surface domains, in which the molecules are densely packed, and a liquid-condensed phase.

A ‘grafting from’ method has been used to fabricate polystyrene/iron-based oxide materials. The styrene conversion is considerably low when initiator-modified iron-based oxides are used. We demonstrate that malononitrile in catalytic amounts strongly enhances the monomer conversion. The hybrid materials are fabricated using a two-step process. First, an atom transfer radical polymerization initiator molecule containing a phosphonic acid group (2-bromo-2-methylpropionic acid 11-phosphonoundecyl ester) is covalently immobilized onto the surface of CoFe2O4 and α-Fe2O3 nanoparticles. In the second step, the polymerization of styrene is performed at the particle surface with and without the addition of malononitrile. Fourier transform infrared spectroscopy, transmission electron microscopy, thermogravimetry and size exclusion chromatography are used to characterize the metal oxide, the initiator molecule grafted onto the metal oxide, the hybrid material and the polymer chains.© 2013 Society of Chemical Industry

Scandium rich cobalt ferrites Co y Fe 3− x − y Sc x O 4 with y ~1 never obtained in bulk could be stabilized in pulsed laser deposited thin films. Scandium contents of up to x =1 are reached. The cell parameter increases versus x as awaited when considering the size of scandium. It is equal to 0.8620 nm for x =1, significantly higher than that of CoFe 2 O 4 (0.8396 nm). The lattice mismatch between the MgO (100) substrate and the scandium-containing spinel leads to an increased roughness. Cobalt is displaced from the octahedral site by Sc and mainly occupies the tetrahedral sites for high x values.

The authors present a study for the first time, an alternative coating route based on an autocatalytic process on metal alloy, to induce Ca–P layer in a way similar to the process of natural bone formation. Ti6Al4V (High-grade titanium aluminium vanadium alloy) substrates were subjected to several pretreatment steps, such as alkali and heat treatments. Afterwards, they were immersed in autocatalytic baths under certain conditions to form Ca–P layers. To check their biochemical stability, the treated substrates were immersed in SBF (simulated body fluid) for 4 days. The biolayers were investigated by FESEM-EDS (field emission scanning electron microscope—energy dispersive x-ray spectroscopy) and FT-IR (Fourier trasform infra-red spectroscopy), before and after immersion in SBF. Biochemical analyses were also performed to evaluate the calcium and phosphorous content in SBF. In autocatalytic baths, Ca–P precipitates on the pretreated substrates after only 2 h. Moreover, after being immersed for 4 days in SBF, the phosphates begin to dissolve and to be replaced by carbonates.

This study presents preliminary results on a coating method based on biomimetic techniques which are designed to form a calcium-phosphate layer very similar to the process corresponding to the formation of natural bone. The proposed deposition route has several advantages of controlled conditions, application to complex shapes, without adverse effect of heating besides being cost effective. Samples were alkali etched and subsequently heat treated. Afterwards, the biomimetic deposition process of a calcium-phosphate coating on the chemically pretreated substrates, were investigated using the SBF immersion route for 4 and 6 days subsequently and discussed. The formed layers were studied using FESEM, confocal microscopy and FT-IR before and after SBF soaking tests. Biochemical analyses of calcium and phosphorous contents in SBF—solutions after samples withdrawal—were performed for the biomimetic assessment of the formed layer along with pH measurements. The data suggests that this method can be successfully applied to obtain deposition of calcium-phosphate and calcium carbonate layers on titanium substrates.

We report on the key effect of NaCl for the stabilization of nanoparticle-decorated microbubbles coated by an anionic perfluoroalkylated phosphate C10F21(CH2)2OP(O)(OH)2 surfactant and negatively charged iron oxide nanoparticles. We show that hollow microspheres with shells of 100-200 nm in thickness can be stabilized even at high pH when a strong ionic force is required to screen the negative charges. Due to the more drastic conditions required to stabilize the hollow microspheres, they appear to be stable enough to be deposited on a surface and dried. That can be a simple way to fabricate porous ceramics.

International audience; Horizontal gene transfers are critical mechanisms of bacterial evolution and adaptation that are involved to a significant level in the degradation of toxic molecules such as xenobiotic pesticides. However, understanding how these mechanisms are regulated in situ and how they could be used by man to increase the degradation potential of soil microbes is compromised by conceptual and technical limitations. This includes the physical and chemical complexity and heterogeneity in such environments leading to an extreme bacterial taxonomical diversity and a strong redundancy of genes and functions. In addition, more than 99 % of soil bacteria fail to develop colonies in vitro, and even new DNA-based investigation methods (metagenomics) are not specific and sensitive enough to consider lysis recalcitrant bacteria and those belonging to the rare biosphere. The objective of the ANR funded project “Emergent” was to develop a new culture independent approach to monitor gene transfer among soil bacteria by labeling plasmid DNA with magnetic nanoparticles in order to specifically capture and isolate recombinant cells using magnetic microfluidic devices. We showed the feasibility of the approach by using electrotransformation to transform a suspension of Escherichia coli cells with biotin-functionalized plasmid DNA molecules linked to streptavidin-coated superparamagnetic nanoparticles. Our results have demonstrated that magnetically labeled cells could be specifically retained on micromagnets integrated in a microfluidic channel and that an efficient selective separation can be achieved with the microfluidic device. Altogether, the project offers a promising alternative to traditional culture-based approaches for deciphering the extent of horizontal gene transfer events mediated by electro or natural genetic transformation mechanisms in complex environments such as soil.

Spinel iron oxide nanoparticles of sizes from 12 to 60 nm have been prepared via a hydrothermal synthesis. Thick films of the Fe3−xO4 nanoparticles deposited on interdigital electrodes were applied as resistive gas sensors. The electrical and gas sensing properties were characterized by impedance spectroscopy using multielectrode substrates. The reducing analytes CH4, NO, H2 and NH3 in N2 as a reference were applied in order to investigate the sensor response, the selectivity and the recovery behavior at temperature between 50 °C and 300 °C. The materials exhibit good sensor responses towards NH3 with low cross sensitivities towards H2 and NO at 250 °C. A linearly increasing sensor response towards NH3 and H2 with decreasing particle size was found.

The fine control of iron oxide nanocrystal sizes within the nanometre scale (diameters range from 2.5 to 14 nm) allows us to investigate accurately the size-dependence of their structural and magnetic properties. A study of the growth conditions of these nanocrystals obtained by thermal decomposition of an iron oleate precursor in high-boiling point solvents has been carried out. Both the type of solvent used and the ligand/precursor ratio have been systematically varied, and were found to be the key parameters to control the growth process. The lattice parameters of all the nanocrystals deduced from X-ray diffraction measurements are consistent with a structure of the type Fe(3-x)O(4), i.e. intermediate between magnetite and maghemite, which evolves toward the maghemite structure for the smallest sizes (x = 1/3). The evolution of the magnetic behavior with nanoparticle sizes emphasizes clearly the influence of the surface, especially on the saturation magnetization M(s) and the magneto-crystalline anisotropy K. Dipolar interactions and thermal dependence have been also taken into account in the study on the nanoscale size-effect of magnetic properties.

Substitution of Fe for Sc in CoFe2O4 spinel structure is presented. All CoFe2−xScxO4 compounds crystallize in the spinel type structure (space group Fd3m). By using X-ray diffraction studies, magnetic measurements and in-field 57Fe Mossbauer spectrometry, the limit of substitution has been determined to be equal to x=0.56. An increase in the cell parameter and the strains and a decrease in the apparent crystallites size are observed. For x>0.3, a partial oxidation of cobalt is evidenced and Co3+ is stabilized in the structure. A ferromagnetic behavior has been observed for all investigated compounds. As x increases, the Curie temperature and the hyperfine fields decrease. Following the Stephenson model, the diminution of TC is ascribed to a decrease of the main JAB interaction.

Nanothermites are versatile pyrotechnic systems composed of a metal oxide and a reducing metal powder, such as aluminum. The high mechanical sensitivity of some of these mixtures (e.g., MnO2/Al) makes their handling hazardous. Enclosing the metal oxide inside carbon nanofibers—thus separating oxidizer and reducing agent—is a new way to lower the sensitivity of nanothermites. In this study, we filled herringbone carbon nanofibers (CNF) with manganese oxide MnOx (x ≈ 1.9) by a two-step opening/filling treatment using nitric acid and molten manganese nitrate, followed by a heat treatment; the resulting nanocomposite is used to prepare a MnOx@CNF/Al nanothermite. A dramatic decrease in the friction sensitivity (threshold >360 N) as compared to a MnO2/Al nanothermite (threshold

ZnO nanorods were synthesized by using a simple two-step hydrothermal approach. The nanorod diameter ranged from 40 to 60 nm and their length was about 2 μm. X-ray diffraction shows good crystalline quality with an axial alignment of the nanorods along the wurtzite c axis. Raman and visible photoluminescence demonstrate that thermal annealing suppresses structural defaults. Photoluminescence experiments performed between 3 and 200 K close to the exciton resonances evidence the presence of optical transitions related to electron-bound exciton scattering. To our knowledge, this is the first time that this feature is identified in ZnO nanorods. The occurrence of such phenomena is an indication that, despite a good crystalline quality, the samples exhibit a strong native n-type character.

Local probe techniques, 57Fe in-field Mossbauer, and 57Fe NMR spectrometries have been combined to describe the magnetic structure of maghemite nanoparticles of 39 (±5) nm in size and commercial maghemite. Maghemite nanoparticles were obtained from oxidation of magnetite nanoparticles. Commercial maghemite consists of nanostructured rods, and the size of crystalline domain fairly compares to that of nanoparticles. The structure of the two samples is a partially disordered spinel structure. Both local probe techniques agree that Fe magnetic moments of octahedral and tetrahedral sites are canted in both systems. It was concluded that the canting originates not only from surface effects but also from the bulk resulting from the disordered spinel structure and the frustrated cationic topology, giving rise to reversed Fe moments.

The interactions of two types of cells (red blood cells, Caco-2 cells) with magnetic iron oxide nanoparticles (non-grafted, citrate-grafted, dendrimer-grafted) of 11 nm in size have been investigated. We focused on two important physiological parameters of the cells, the intracellular pH and the intracellular Ca2+ content. The results show that the nanoparticles do not have a significant influence on the pH and Ca2+ content of Caco-2 cells. The Ca2+ content of red blood cells is also not affected but the intracellular pH is slightly reduced.

Dense monolayer assemblies of iron oxide nanoparticles have been obtained on large areas using the Langmuir–Blodgett technique. The density and ordering of the film were found to depend on the quality of the nanoparticle suspensions, which should display monodisperse nanoparticles and no free molecules. A modification of nanocrystals magnetic properties was noticed between the random configuration (powder sample) and the assembly in monolayer (Langmuir–Blodgett). The organisation in film is suggested to induce an enhancement of magnetic interactions.

J. Santoyo-Salazar*, M. A. Castellanos-Roman, B. Gomez-Looh, D. Ihiawakrim, C. Lefevre, G. Pourroy. 1 Institut de Physique et Chimie des Materiaux de Strasbourg, UMR CNRS-ULP-ECPM 7504, 23, rue du Loess, BP 43, 67034 Strasbourg cedex 2, France. 2 Facultad de Quimica, Departamento de Quimica Analitica, Universidad Nacional Autonoma de Mexico, Mexico D.F., 04510, Mexico. 3 Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, AP 70-360, Mexico D.F. 04510, Mexico.

The effect of surface inorganic−organic interactions on magnetic and structural properties of iron oxide magnetic nanoparticles functionalized by lipophilic stilbene molecules has been investigated. The molecules have been grafted through either phosphonate or carboxylate coupling agents. Mossbauer spectra recorded at 300 and 77K suggest a global composition of Fe2.82O4 for the two types of functionalization. Complementary in-field Mossbauer and SQUID measurements have demonstrated that the nanoparticles consist in a magnetite core surrounded by an oxidized layer. The oxidized shell exhibits a spin canting in the carboxylate case leading to a decrease of the net magnetization of the oxide nanoparticle. No canting occurs in the phosphonate case, and the magnetic properties are therefore preserved. The magnetic properties thus depend on the coupling agent, e.g., surface interactions. This result is of primary importance to tune the magnetic properties of functionalized nanoparticles for biomedical and high ...

The design and the functionalisation of nanoparticles is a promising way to elaborate new functional materials, with combined or coupled properties (magnetic, optical, optoelectronic …). In this context, the direct binding of functional organic conjugated molecules (stilbene derivative) onto the surface of monodisperse Fe 3 O 4 magnetic nanoparticles has been studied. Monodisperse Fe 3 O 4 nanoparticles have been synthesized by adjusting the conditions of precipitation and growth and then stilbene derivatives have been grafted onto the surface of these nanoparticles using either phosphonate or carboxylate groups as coupling agents. The functionalised nanoparticles have been characterized before and after grafting by several techniques (XRD, UV, TEM). Studies have demonstrated that the phosphonate coupling agent allows a higher grafting rate than with the carboxylate coupling agent. The nanoparticles functionalised via carboxylate groups are less stable than those functionalised with phosphonate groups mainly due to a strong P–O–Fe bonding. The coated magnetite nanoparticles retain their intrinsic magnetic properties.

International audience; The microwave properties of sheets containing silica-coated NiFeMo flakes are investigated and discussed according to the sheet structure, the silica layer uniformity and thickness. Commercial NiFeMo flakes are coated using the Stoeber method and embedded in polymer using the doctor blade process. The silica layer thickness is estimated by transmission electron microscopy (TEM) and the coating quality is probed by scanning electron microscopy (SEM). The in-plane orientation of magnetic moments within the sheet is evidenced by 57Fe Mössbauer spectrometry. As a result, the permittivity of composites is strongly reduced when the NiFeMo flakes are completely coated, whereas the permeability level is weakly and progressively altered when the silica thickness increases. We show that the frequency range for microwave absorption can be tuned according to the silica thickness and the flake loading. Reflection losses of −13 dB are obtained in the 1–2 GHz range for a normal incident electromagnetic wave interacting with 3 mm sheets backed by a perfect conductor and loaded with silica (90 nm width)-coated NiFeMo flakes.

A novel zinc hydroxy acetate hydrogen carbonate Zn5(OH)8.2(CH3COO)(HCO3)0.8·1.9H2O, isomorphous to Zn5(OH)8(CH3COO)2·xH2O, has been obtained by the reaction of zinc acetate dihydrate in aged ethylenediamine. This phase allows the growth of large arrays of oriented and crystallized nanorods up to 8 μm in length on a substrate, without crystallization of additional particles.

Scandium rich cobalt ferrites Co y Fe 3− x − y Sc x O 4 with y ~1 never obtained in bulk could be stabilized in pulsed laser deposited thin films. Scandium contents of up to x =1 are reached. The cell parameter increases versus x as awaited when considering the size of scandium. It is equal to 0.8620 nm for x =1, significantly higher than that of CoFe 2 O 4 (0.8396 nm). The lattice mismatch between the MgO (100) substrate and the scandium-containing spinel leads to an increased roughness. Cobalt is displaced from the octahedral site by Sc and mainly occupies the tetrahedral sites for high x values.

Dendronized nanoparticles were designed for the bimodal (optical and magnetic) detection of lymph nodes with a hand-held probe during surgery. Patent Blue VF dye and iron oxide nanoparticles with 20 nm diameter, displaying high magnetization and located at the superparamagnetic/blocked monodomain boundary, were associated through a dendritic PEGylated coating to obtain stable water suspensions. Conjugation procedures (the sulfonamide link formed between the PEGylated dendron and the dye, together with the phosphonate anchoring on the iron oxide surface) were shown to be strong enough to survive in vivo conditions when the prepared nanohybrids were tested in an inflammatory node model. Moreover, magnetization of 20 nm nanoparticles increased when dendrons were grafted onto the surface, showing that they are good candidates for magnetic particle imaging, which requires high magnetization values. Preliminary lymphatic node uptake experiments performed in an inflammatory animal model showed higher uptake of the 10 nm nanoparticles relative to that of 20 nm nanoparticles. The highest probe concentration was reached 2 d after injection. INTERREG IV Oberrhein (Project A21)

The functionalization of spherical superparamagnetic iron oxide nanoparticles (SPION) of 10 nm with a linear monophosphonate (L1) and also PEGylated mono-phosphonated dendrons of growing generation (D2-G1, -G2 and -G3) yielded dendritic nano-objects of 15 to 30 nm in size, stable in physiological media and showing both renal and hepatobiliary elimination. The grafting of the different molecules has been confirmed by IR spectroscopy and elemental analysis. The colloidal stability of functionalized NS10 has been evaluated in water and in different physiological media. All functionalized NS10 were stable over a long period of time and displayed a mean hydrodynamic diameter smaller than 50 nm whatever the molecule architecture or dendron generation. Only the NS10@L1 showed less stability in biological media at high ionic concentration. NMRD profiles and relaxivity measurements highlighted the influence of the molecule architecture on the water diffusion close to the magnetic core thus influencing the relaxation properties at low magnetic field. Coupling of a fluorescent dye on the functionalized NS10 allowed investigating their biodistribution and highlighting urinary and hepato-biliary eliminations.

CoFe2/CoFe2O4 bilayers were made by pulsed laser ablation of a CoFe2 target on Si(1 0 0) substrates. The metallic layer was deposited first, in vacuum. The oxide was then deposited in an oxidizing O2:N2 (20:80) atmosphere. Two different procedures were used for the introduction of the oxidizing atmosphere in the deposition chamber: the laser ablation of the target was either stopped (discontinuous deposition process) or maintained (continuous deposition process) during the 20 min necessary for the establishment of the desired O2:N2 pressure. In both cases, the different electronegativities of Fe and Co cause an important modification of the Fe/Co ratio at the metal/oxide interface, with a depletion of Fe in the metal region and of Co in the oxide region. In the continuous procedure, the combination of the kinetic energy given by the ablation process to the Fe and Co adatoms with the one they get from their different affinity towards oxidation allows the formation of a low roughness metal/oxide interface with a high (1 1 1) preferred orientation of the CoFe2O4 layer, an induced re-crystallisation of the metal layer underneath and an unusual antiferromagnetic metal/oxide magnetic coupling.

Ni 0.5 Zn 0.5 Fe 2 O 4 ferrite platelets of 5 to 300 μm have been obtained by reaction in a molten salt between hematite platelets, NiO and ZnO powders. The hematite platelets are obtained by a hydrothermal treatment in an alkaline medium between 180 and 270 °C through a dissolution-recrystallization mechanism from maghemite which crystallizes first. The key parameter for size control is the mixture alkalinity. The largest platelets are obtained for [Fe 3+ ] = 2.0 mol dm −3 and [OH − ] = 15.3 N. The size distribution is narrow and the aspect ratio about 30. The reaction with nickel and zinc oxides yields the formation of polycrystalline platelets through a topotactic reaction allowing the platelet morphology, initial shape and size to be conserved. SEM observations reveal the ferrite platelets are made of adjacent micronic ferrite crystals with their [111] faces parallel to the platelet surface. Increasing the reaction temperature promotes an enlargement of the [111] faces. The respective solubilities of oxides and ferrites in the molten salts control the ferrite stoichiometry. KCl as a flux gives better results than NaCl with no modification of the crystal shape and no ZnO loss.

Thin films of CoFe 2 O 4 have been fabricated by pulsed laser ablation of a metallic CoFe 2 target at two different temperatures (200 and 400 °C) and in various O 2 :N 2 , 20:80 pressures [from 0.7 Pa (5×10 -3 Torr) up to 26.7 Pa (2×10 -1 Torr)]. Too low pressures resulted in an insufficient oxidation of the deposited material and an antiferromagnetic (Fe,Co)O phase is observed together with CoFe 2 O 4 . A minimum pressure of 6.7 Pa was found necessary to obtain pure CoFe 2 O 4 films with magnetic properties close to the bulk. The higher the pressure and the temperature, the larger was the roughness of the films. The optimum deposition temperature and pressure to obtain flat (3 nm rms roughness) CoFe 2 O 4 films were, respectively, 200 °C and 6.7 Pa.

This paper presents a study of the magnetic behaviour of hard ferrimagnetic oxide/soft ferromagnetic metal CoFe2O4/CoFe2 bilayers. Such bilayers with a constant oxide thickness of 150 nm and thickness of metal varying between 8 and 25 nm were elaborated by pulsed laser deposition of a metallic CoFe2 target in appropriate atmospheres. An exchange coupling of about 0.3 erg / cm 2 between the two layers was put in evidence. The in-plane bulk and interface contributions to the magnetic anisotropy of the soft layer were found to be perpendicular to each other with estimated values of 170 kerg / cm 3 and 0.6 erg / cm 2 respectively.

In this work the structural and magneto-transport properties of the Sr 2 FeMoO 6 double perovskite prepared using two elaboration processes are presented. The first process is the most used solid-state reaction technique starting from three materials: Fe 2 O 3 , SrCO 3 and metallic MoO 3 with the appropriate amounts. For this process, treatment conditions have been optimized in order to reduce the SrMoO 4 amounts in the final compound. The best results have been obtained after annealing the mixture during 1 h at 700 °C under reducing 5% H 2 –95% N 2 atmosphere followed by calcinations at 1200 °C under Ar atmosphere during 10 h. X-ray diffraction measurements have shown that the phase can be indexed within the I4/mmm space group indicating a tetragonal distortion. The magneto-transport measurements have shown the highest saturation magnetization value reaching 26.7 emu/g at 300 K and a magnetoresistance (MR) of 2.5%. For the second process, the phase has been elaborated using several steps and reacting at each step only two materials. In this case X-ray diffraction shows that the final compound is a single phase with the same space group as for the previous one. In contrast, the saturation magnetization is slightly smaller with 21 emu/g, while, at the opposite, the magnetoresistance is higher reaching 3.6%. These results will be discussed in correlation with the structural results.

We report on the possibility to prepare CoFe 2 /CoFe 2 O 4 bilayers and multilayers by deposition of a CoFe 2 layer followed by a partial oxidation in an Ar–O 2 plasma. The CoFe 2 alloy was deposited by argon sputtering onto a glass substrate and the deposition/oxidation procedure was repeated to obtain multilayered stacks. The prepared films are polycrystalline. The grains in the multilayer have an average size of ca. 500 A. The only phases detected by selected area diffraction patterns are a bcc CoFe 2 alloy and a spinel CoFe 2 O 4 phase. High resolution transmission electron microscopy images show that the ferrite and the iron–cobalt alloy layers are flat and have a constant thickness over several thousands of A. Our study of the oxidation process for varied plasma powers and oxidation durations shows that a maximum thickness of approximately 34 A can be obtained for the oxide. Despite the polycrystalline character of the film, coherent lattice fringes are observed through several bilayers, indicating not only a coherent formation of the oxide on top of the metal grains but also an epitaxial growth of the metal layers subsequently deposited onto the oxidised layers.

The study of the CoFe 2 /CoFe 2 O 4 system is of great interest due to its potential integration in magneto-resistive devices. CoFe 2 /CoFe 2 O 4 multilayers were elaborated by plasma oxidation of sputtered CoFe 2 layers. Exclusive attention is paid, in this paper, to the study by high resolution transmission electron microscopy of the crystallographic relationships between the metal and the oxide networks. The oxide was observed to grow epitaxially from the metal with the following relationship : oxide (1 0 0)[1 0 0] ∥ metal (1 0 0)[1 1 0]. This epitaxial relationship was observed even though the metal (CoFe 2 alloy) did not always present its (1 0 0) face to the surface and was oxidised by the violent process that is plasma oxidation. Our conclusion that the growth of epitaxial metal/oxide multilayers by sputtering only depends on the epitaxial growth of the first deposited metal layer is of major interest.

The complementarity between 57 Fe Mossbauer spectrometry and classical methods of powder characterizations is pointed out for determining the formula of metal-ferrite composites (Fe $_p^0$ Co $_{1-p}^0$ ) a (Co x Fe $_{3-x-t}$ $\square_t$ O 4 ). It is shown that X-ray diffraction is essential to determine the composition of the metal, while TG measurements in air give an approximate value for the metal ratio. In-field spectrometry is expected as the most suitable tool to determine the Fe sites occupancy, although the complex hyperfine structure might originate some misfits. The composites formulae were therefore determined by selecting the set of refined Mossbauer parameters that were in best agreement with the TG measurements. Magnetic measurements prove the validity of such an approach.

Fe0–Co0/Co-magnetite composites are synthesized in an autogeneous pressure between 100°C and 250°C in a KOH medium 0.5–14 N. X-ray diffraction and 59Co NMR spectroscopy exhibit various CoFe alloys: the ordered B2 CoFe alloy, a bcc CoFe alloy with a peculiar short range order encountered in thin films and a CoFe alloy isomorphous to α-Mn. The first occurs at low [KOH], the second is favoured by high [KOH]. The α-Mn structure is favoured for [KOH] close to 9 N, Co/Fe ratios between 0.4 and 0.5 and low temperatures of synthesis. A low [KOH] favours nucleation leading to octahedra of 150–200 nm. [KOH] of 12–14 N favours particle growth. The metal occurs in round ball-shaped particles of 10–20 nm embedded within the spinel.

This paper reports the microwave-hydrothermal treatment of alcoholic solutions of ferrous chloride (FeCl2) and sodium ethoxide (EtONa) solutions with a microwave autoclave designed by the authors (the RAMO system). Depending on the initial concentrations, hematite (α-Fe2O3), spinel phase (Fe3 − xO4) or iron-magnetite (Fe0-Fe3O4) nanocomposites are obtained with a lower grain size compared to conventional composites. Indeed, X-ray diffraction (XRD) analysis reveals grain sizes close to 20 nm for magnetite and 60 nm for metallic iron. However, the amount of metal is smaller (close to 11%). Furthermore, these particles are inert in the ambient atmosphere. Consequently, the RAMO (French acronym of Reacteur Autoclave MicroOnde) system appears to provide an efficient source of energy in rapidly producing inert powders of iron, magnetite and iron-magnetite composites.