On the effect of temperature on the insertion of zinc into hydroxyapatite.

International audienceRietveld analysis on X-ray powder diffraction patterns recorded from 28 hydroxyapatite samples containing various amount of zinc (0, 1.6, 3.2 and 6.1 wt. Zn %) and heat treated at various temperatures (between 500°C and 1100°C) have allowed to finely characterize the Zn insertion mechanism into the HAp crystal structure. The formation of Zn-doped HAp was achieved above 900°C only. Zn-doped HAp has the Ca10Znx(PO4)6(OH)2-2xO2x (0 < x ≤ 0.25) chemical composition with a constant Ca/P ratio of 1.67 due to the insertion mechanism into the hexagonal channel (partial occupancy of the 2b Wyckoff site with formation of linear OZn- O entities). Samples heat treated at 500 °C were almost single phase, HAp did not incorporate Zn and about half of the Zn atoms incorporated during the synthesis are not observable by X-ray powder diffraction (contained in an amorphous compound or physisorbed at the HAp surface). The reversible formation of Zn-doped β-TCP phase was observed at 600°C, reached its maximum content at 900°C and almost vanished at 1100°C. The results presented here strengthen the recently described mechanism of Zn insertion in the interstitial 2b Wyckoff position of the HAp structure, and explain the origin of the contradictory reports in the corresponding literature

New Strontium-based Bioactive Glasses: Physicochemical Reactivity and Delivering Capability of Biologically Active Dissolution Products

International audienceThe development of bone tissue regeneration calls for biomaterials able to release biologically active substances in a controlled manner after implantation. In this context, strontium-doped bioactive glasses are of major interest; their key property relies on the increased kinetics of surface reactions, along with the release of critical concentrations of ionic dissolution products capable of stimulating cellular responses. In this paper, we report a complete evaluation of the in vitro reactivity of new SiO2–CaO–SrO and SiO2–CaO–P2O5–SrO bioactive glasses. In contact with simulated acellular physiological fluids, these materials induce the formation of a calcium phosphate surface layer that closely resembles to the biological apatite present in bones. Compared to strontium-free materials, the dissolution of SiO2–CaO–SrO and SiO2–CaO–P2O5–SrO glasses is reduced. However the surface layer is more quickly transformed into a bone-like apatite phase, according to the kinetics of evolution of the Ca/P atomic ratio. Evidences of the presence of Sr at the glass/biological fluids interface were obtained, along with the demonstration that this element is released in physiological concentrations into the biological environment. Knowing the well-recognized beneficial effects of strontium on cell activity and bone remodeling, this crucial result gives high hopes for the development of innovative applications based on Sr-doped glasses in treatment of osteoporosis and tissue engineering

Crystallization of carbon tetrachloride in confined geometries

International audienceThe thermal behaviour of carbon tetrachloride confined in silica gels of different porosity was studied by differential Scanning Calorimetry. Both the melting and the phase transition at low temperature were measured and found to be inextricably dependant upon the degree of confinement. The amount of solvent was varied through two sets of experiments, sequential addition and original progressive evaporation allowing the measurement of the DSC signals for the various transitions as a function of the amount of CCl4. These experiments allowed the determination of transition enthalpies in the confined state which in turn allowed the determination of the exact quantities of solvent undergoing the transitions. A clear correlation was found between the amounts of solvent undergoing the two transitions (both free and confined) demonstrating that the formation of the adsorbed layer t does not interfere with the second transition. The thickness of this layer and the porous volumes of the two silica samples were measured and found to be in very close agreement with the values determined by gas sorption

Isothermal Crystallization Kinetics of In Situ Photo and Thermo Aged Poly(Ethylene Oxide) Using PhotoDSC

Isothermal crystallization of a high molecular weight PEO (Mw= 4.000.000) has been investigated using photoDSC. Combining light irradiation, heating and DSC analysis, photoDSC demonstrates a good capability to follow the in situ photo and thermo aging of semi crystalline polymers. Isothermal crystallization of PEO has been performed at 55°C. After aging at different temperatures ranging from 0 to 90°C and for various periods of time, the kinetics of this crystallization has been found fitting Avrami theory. Avrami exponent, n, was found between 0.9 and 1.4 revealing a one-dimensional growth process. It was also found that isothermal crystallization rate (i.e. reciprocal crystallization half-time) was time exposure, aging temperature and light intensity dependent which makes this kinetics parameter a good indicator to follow and to compare the degradation of the semi-crystalline polymers

Concentration effect on the scintillation properties of Sol-Gel derived LuBO3 doped with Eu3+ and Tb3+.

International audienceLu1-xEuxBO3 and Lu1-xTbxBO3 powders have been prepared by a sol-gel process with 0 < x < 0.15 for Eu3+ and 0 < x < 0.05 for Tb3+. The purity of powders has been verified by X-Ray diffraction and the results confirm that all the materials have the vaterite type even if the calcination has been performed at 800°C. Furthermore, the solid solution for LuBO3 vaterite is observed up to x=0.15 and x=0.05 for europium and terbium ions respectively. So doping with Eu3+ or Tb3+ ions does not affect the structure. These materials have also been analyzed by Fourier Transform Infra Red Spectroscopy. The morphology of the powders has been studied by Scanning Electron Microscopy and shows a very nice morphology with small spherical particles with narrow size distribution. Optical properties have then been studied to confirm the effective substitution of Eu3+ or Tb3+ for Lu3+ ions and to determine the materials scintillation performances. The optima, in term of scintillation yield, are obtained for Eu3+ and Tb3+ concentration of x=0.05 in both cases. The afterglows have also been measured and confirm the potentiality of these materials as scintillators

Precursor-Directed Assembly of Complex Oxide Nanobeads: The Role of Strongly Coordinated Inorganic Anions

International audienceThe use of an inorganic perrhenate ligand in the structure of early-transition-metal alkoxide precursors permits to achieve uniform self-assembly of the primary nanoparticles produced by their hydrolysis. The latter has been carried out in a hydrocarbon reaction medium by the addition of water with vigorous stirring, either in the pure form or in solutions in parent alcohols. The self-assembly is guided by the surface charge enhanced by the presence of strongly coordinated anions as determined by zeta potential measurements. The aggregation process has been followed in real time by nanoparticle tracking analysis (Nano Sight technique). The reaction products are spherical aggregates with a size that can be efficiently controlled through the polarity of the reaction medium. The produced nanobeads have been characterized by TEM, SEM-EDS, DLS, nitrogen adsorption, and FTIR The coordination of metal centers has been investigated using EXAFS spectroscopy. The aggregates remain amorphous on thermal treatment of up to 700 degrees C (24 h treatment) but crystallin when treated at 1000 degrees C. This latter process is associated with the total loss of rhenium content and offers early-transition-metal oxides as products

Polymer Microstructures. Modification and Characterisation by Fluid Sorption

International audiencePolymer micro-organisation can be modified by combination of the three constraints, thermal, hydrostatic and fluid sorption. In selecting the fluid's nature, chemically active or inert, and its physical state, liquid or supercritical, new “materials” can be generated. In addition, the interplay of temperature and pressure allows tailoring the obtained material structure for specific applications. Several complementary techniques have been developed to modify, analyze and characterize the end products: scanning transitiometry, vibrating wire (VW)-PVT coupling, thermoporosimetry, temperature modulated DSC (TMDSC), sorptometry. The great variety of possible applications in materials science is illustrated with different polymers which can produce materials from soft gel to rigid foams when submitted to fluid sorption, typical fluids being methane, or a simple gas (CO2 or N2). Absorption of an appropriate fluid in a cross linked polymer leads to a swelling phenomenon. Thermoporosimetry is a calorimetric technique developed to measure the shift by confinement of thermal transition temperatures of the swelling fluids, which can be currently used solvents or mercury. Application of thermoporosimetry to a swollen cross linked polymer allows to calculate the mesh size distribution and to evaluate the degree of reticulation of the polymer. The same technique can be applied to characterise the pore size distribution in a foamed polymer

Scintillation of Sol-Gel derived Lutetium orthophosphate doped with rare earth ions.

In this paper, the synthesis, the characterization and the scintillation properties of LuPO4 doped, with several concentrations of Ce3+, Eu3+ and Tb3+ ions, are presented. These materials have been synthesized by sol-gel process. The purity of powders has been verified by X-Ray diffraction and the results confirm the xenotime structure of all the materials. A thermogravimetric analysis allows the obtention of informations on the crystallisation of LuPO4 and the study of its evolution from the amorphous to crystalline form. The morphology of the powders has been studied by Scanning Electron Microscopy and shows that the powders are constituted of small particles with narrow size distribution. Optical properties have been studied in order to determine the scintillation performances of these materials. The optima are obtained for Ce3+, Eu3+ and Tb3+ concentration of respectively 0.1%, 10% and 5% with high scintillation yields. This study thus confirms the potentialities of these materials as scintillators

Influence of mesostructuration on the reactivity of bioactive glasses in biological medium: a PIXE-RBS study

Building mesostructured biomaterials is a challenging and exciting task that has attracted much attention because of their use as drug carriers or drug delivery systems. In the case of bioactive materials, the mesostructuration can also deeply impact their physico-chemical properties and the reactivity. In this study, we show how highly ordered mesoporosity influences the early steps of the biomineralization process and the reactivity in binary (SiO2–CaO) and ternary (SiO2–CaO–P2O5) bioactive glasses. Conventional porous sol–gel glasses were synthesized using a classical route, while mesostructured glasses were developed using a non-ionic surfactant. Textural properties of these materials have been characterized. The in vitro biomineralization process was followed, using Particle Induced X-ray Emission (PIXE) associated to Rutherford Backscattering Spectrometry (RBS), which are efficient methods for a highly sensitive multi-elemental analysis. Elemental maps of silicon, calcium and phosphorus were obtained at a micrometer scale and revealed for the first time a bulk reactivity for mesostructured glasses. This is a major advantage over conventional glasses, for which the first steps of biomineralization are limited to the periphery of the material. Their enhanced bioactivity combined with their possible use as drug-delivery systems make them promising candidates for bone regeneration

Micro-PIXE-RBS methods highlighting the influence of phosphorus on the in vitro bioactivity of sol-gel derived glass particles in the SiO2-CaO-P2O5 system

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