Didier Bernache-Assollant

Accurate characterization of pure silicon-substituted hydroxyapatite powders synthesized by a new precipitation route

This paper presents a new aqueous precipitation method to prepare silicon-substituted hydroxyapatites Ca10(PO4)6-y(SiO4)y(OH)2-y(VOH)y (SiHAs) and details the characterization of powders with varying Si content up to y=1.25molmolSiHA(-1). X-ray diffraction, transmission electron microscopy, solid-state nuclear magnetic resonance and Fourier transform infrared spectroscopy were used to accurately characterize samples calcined at 400°C for 2h and 1000°C for 15h. This method allows the synthesis of monophasic SiHAs with controlled stoichiometry. The theoretical maximum limit of incorporation of Si into the hexagonal apatitic structure is y<1.5. This limit depends on the OH content in the channel, which is a function of the Si content, temperature and atmosphere of calcination. These results, particularly those from infrared spectroscopy, raise serious reservations about the phase purity of previously prepared and biologically evaluated SiHA powders, pellets and scaffolds in the literature.

Termal decomposition of carbonated calcium phosphate apatites

The thermal stability of AB-type carbonated calcium phosphate apatites prepared by precipitation from aqueous media was studied. The behavior of powders was investigated using temperature programmed XRD, infrared spectroscopy and thermogravimetry. In N2 atmosphere, two successive peaks of decarbonatation with maxima at about 700 and 950°C occurred. This behavior is explained by different substitution modes for carbonates in the apatite. The decarbonatation peaks were shifted to higher temperature under CO2 (around 900 and 1150°C). The analysis of the thermal stability allowed further densification of carbonate apatite ceramics without important carbonate loss.

Physico-Chemical Characterization and In Vitro Biological Evaluation of Pure SiHA for Bone Tissue Engineering Application

Studies about silicon-substituted hydroxyapatites exhibit several shortcomings that leave unanswered questions regarding the properties and subsequent biological outcomes generated by this biomaterial. Firstly, samples characterization is often incomplete, meaning that phase purity on the pellet surface is not assured. In fact, ceramic materials used in literature that are claimed to be pure are actually polluted through second phase as superficial polymerized silicate. In this study, we have successfully synthesized a phase pure silicon hydroxyapatite powder Ca10(PO4)5.5(SiO4)0.5(OH)1.5 (Si0.5HA) compressed this powder into pellets, sintered them, and evaluated the biological response of osteoblast cells (C3H10 line) seeded on the pellet surface. Besides, the solubility in aqueous media of HA and Si0.5HA pellets were determined through static experiments. These tests attempt to provide a comprehensive picture of the cellular response to the SiHA material, in order to determine the mechanism by which Si evokes the improved in vitro biological outcomes described in the literature. Results revealed first an equivalent solubility of Si0.5HA and HA pellets, and second that cells do not react favourably to the pure SiHA surface.

Synthesis and Characterization of Beta Tricalcium Phosphate

This work aimed to develop apatitic tricalcium phosphate via an aqueous precipitation process. The results showed high variability of Ca/P ratio of powders with the ripening time, and more particularly an increase of the Ca/P value with this durati on. Temperature and pH of synthesis also play an important role in the composition of the precipitate. Hot pressing was used to fully densify the material at a temperature below the β α transition, that occurs at 1150°C, and mechanical characterizations of dense TCP were performed.

Synthesis and Characterisation of Oxide Ions Conductors with the Apatite Structure for Intermediate Temperature SOFC

Silicated rare earth apatite with formula La9,33(SiO4)6O2 has been prepared by solid state reaction synthesis at high temperature. The reagents (La2O3 and SiO2) have first been characterised. Then the synthesis process was studied and optimised. Samples with various densities (from 70 to 95% of the theoretical value) have been obtained by hot pressing at 1400°C and by sintering at 1550°C. The presence of secondary phases leads to the formation of a liquid phase at achieving sintering at temperatures above 1600°C. Electrical properties of the whole samples have been characterised between 400 and 900°C by the complex impedance method. Conductivity values of about 2.10 -4 S/cm have been measured at 700°C. The samples present activation energies of less than 1 eV, which is a typical value for such ionic conductors.

Synthesis and Characterization of Cx-Siy-HA for Bone Tissue Engineering Application

The main goal of this work is to prepare carbon and silicon co-substituted calcium hydroxyapatite (Cx-Siy-HA) for bone tissue engineering application. This study includes the synthesis of pure powders with a controlled amount of carbonate (x) and silicate (y) ions within the apatite structure, their characterization with the establishment of database for different compositions, and the manufacture of dense bioceramics. Carbon-silicon co-substituted hydroxyapatite (C0.5-Si0.5-HA) powders are synthesized by aqueous precipitation. According to structural, spectroscopic and elemental characterizations, silicate and carbonate are included in the apatite lattice and their stoichiometries are controlled. The heat treatments under CO2 atmosphere allow the sintering of pellets without decomposition of the apatite structure.

Cadmium Uptake by Synthetic Hydroxyapatite in Aqueous Solution

This study deals with the understanding of the cadmium uptake mechanism by synthetic stoechiometric hydroxyapatite (Ca10(PO4)6(OH)2) in aqueous solution. Three parameters were studied : the powder specific surface (SBET), the initial Cd 2+ concentration ([Cd 2+ ]o) and the time of the sorption experiments (tcontact). We have find that the quantity of cadmium immobilized by the hydroxyapatite is mainly controlled by the sample specific surface area. The analyses after the reactions of immobilization, indicate the presence of cadmium adsorbed to the surface of crystallites and a solid solution of the Ca(10-x)Cdx(PO4)6(OH)2 type (with x = 1 + 3y and 1 < x < 4).

Synthesis and Sintering of Carbonated Apatites

AB carbonated apatites (AB-CO 3-Aps) could be synthesized by precipitation reactions in aqueous media. The weight content of carbonate in the apatitic structur e is controlled by the CO 3 2/PO4 3molar ratio of initial reagents (C/P). When (C/P) value is a bove 3/2, CaCO3 appears as a second phase. The sintering of AB carbonated apatites was realized in dry CO2 atmosphere in order to prevent a total loss of carbonate species. The sintering tempera ture decreases when the initial carbonate content increases. The resulting densified material is an AB-CO3-Aps more carbonated in A sites than the initial powder.