Papers by Author: Eric Champion

Abstract: The aim of this work was to identify robust and reproducible signatures characterizing the different steps of bone cell differentiation, from precursors to mature bone cells, using approaches allowing characterization by label-free imaging. Human mesenchymal stromal cells (hMSCs) were cultured either in a growth medium (GM), unable to induce cell differentiation by itself, or in an osteogenic differentiation medium (ODM) on hydroxyapatite ceramics or borosilicate glass. Cell density as well as cell structure, size, and morphology were investigated. A fluorescence microscopy-based approach was followed, using fluorescent labelling of cell features. Some early morphological changes of hMSC during osteogenic differentiation were identified as soon as 48h that were accentuated after 7 days of culture. Cell density was higher when cells were cultured in GM and the cells exhibited significantly smaller nuclei (size ratio about 1.3-1.5) than those cultured in ODM, regardless of the culture support. In ODM, the cells were also of bigger size (1.2 to 1.5 times) and their focal adhesions were reinforcedType I collagen, a gold standard marker of osteogenic differentiation, appeared more intense in ODM. These cell features can be determined using multimodal label-free imaging methods to characterize the differentiation state of hMSCs at the biomaterial surface. They give rise to new cost-effective approaches to investigate cell behavior by suppressing the chemical markers and reducing both the number of needed samples and the requested time to do so.

Abstract: Hydroxyapatite (HA) ceramic scaffolds are commonly used as bone graft substitutes. Design of such scaffolds is a challenge to improve biological properties and extend the applications of HA ceramics in the field of bone tissue engineering. In this work, we investigated the processing and the in vitro properties of HA ceramic scaffolds mimicking human trabecular bone architecture. Samples of human tibial trabecular bone were collected (University Hospital Center of Limoges) and scanned by X-Ray μ-computed tomography (μ-CT) to generate 3D model database. From this computer-aided design, HA ceramic scaffolds were shaped layer-by-layer by additive manufacturing using laser stereolithography (SLA). Then, green parts were sintered to obtain dense ceramic scaffolds. The shaped parts were compared to the model (wall thickness, size, and geometry of the porous network) using image analysis. A good agreement was found. Only small differences were detected due to a light overpolymerization or to some unprinted very small details that were not linked to a polymerized area of the previous layer. Due to part shrinkage during sintering a magnifying factor has to be applied to the scanned CAO model to match the real dimensions of the trabecular bone sample. Human mesenchymal stem cell (hMSC) cultures were performed to investigate the biological properties of these scaffolds (cell attachment and proliferation of hMSC). These preliminary biological evaluations show the good biocompatibility and cell adhesion of the HA substitute. This work evidences the efficiency of SLA to produce ceramic scaffold architectures mimicking that of the natural trabecular bone with promising biological behavior.

Abstract: Spherical porous calcium phosphate pellets were fabricated by high shear wet granulation using native starch as a binder. After a heat treatment to eliminate the organic template, pellets were loaded with ibuprofen by solvent evaporation method. In vitro drug release kinetics was determined using an USP II apparatus (Prolabo Dissolution Tester, France). Results showed the interest of the calcination and of the increase in the binder-porogen content, to improve the drug loading (higher drug content) and prolong the release of the drug substance.

Abstract: The purpose of this study was to develop bioceramics with a well-defined porous structure in order to control drug loading and release over time. Porous structures were obtained through colloidal processing, using polymethyl methacrylate (PMMA) microspheres as templates (core) and hydroxyapatite (HA) nanoparticles as inorganic building blocks (shell). Dispersed HA suspensions were prepared and their electrokinetic properties were studied to determine a dispersant giving a high positive zeta potential (opposite to the negative zeta potential of PMMA). Upon mixture of well-dispersed HA and PMMA suspensions of opposite charge, core-shell structures were formed via heterocoagulation. After consolidation, polymers were removed by calcination, resulting in a porous structure of controlled size and distribution.

Abstract: Pure b-tricalcium phosphate (bTCP) and Si-substituted b-tricalcium phosphate powders with compositions ranging from x = 0.01 to 0.20 were synthesized using a wet precipitation method. The results showed that the addition of Si decreased the maturation time of single-phase Si-substituted bTCP. For longer maturation time, other phases were observed such as hydroxyapatite (HA) and a-tricalcium phosphate (aTCP). The Si incorporation was confirmed by X-ray diffraction with Rietveld refinement, indicating an increase of the lattice volume from 3524.88 Å3 for pure bTCP to 3527.41 Å3 with increasing Si content.

Abstract: This work aimed at preparing dense and monophasic silicated hydroxyapatite ceramics over the range 0 ≤ x ≤ 1.0 mol of silicon. The synthesis of the powder via an aqueous precipitation process followed by an adapted thermal treatment showed that it was possible to obtain dense single-phased apatite ceramics containing up to 0.6 mol of silicon. The in vitro biological characterization of these materials was performed.

Abstract: The removal of cadmium from water by fixation into a calcium phosphate apatite Ca10(PO4)6(OH)2 (CaHA) was investigated in batch experiments. These ones were carried out using a wide range of initial Cd2+ concentration, three different temperatures, and several CaHA surface areas. The amount of immobilized cadmium was proportional to the surface area of CaHA, whatever the experimental parameters might be. It could reach 7.1 mol of Cd per mol of starting CaHA. Thermal and XPS analyses on the exchanged powders proved that a part of cadmium was quickly adsorbed at the grains surface in the form of hydrated complexes [Cd(OH2)n]2+. The latter were formed by an ionic exchange between adsorbed calcium and cadmium of the solution. Adsorption reaction was mainly limited by the number of specific sites available on the grains surface. Structural analyses showed that another part of Cd was slowly incorporated into a solid solution Ca10-xCdx(PO4)6(OH)2 (CaCdHA) onto the CaHA crystals surface. Results demonstrated unambiguously that the incorporation process was a surface precipitation and not an intracrystalline diffusion.