Edouard Jallot

This communication reports a new process for the synthesis of bioactive glass foams. This process is based on the use of gelatin as a template during the foaming of a sol, and the gelled gelatin template formed in situ maintains the foam structure during further condensation of the glass network.

In this work, the physicochemical reactions occurring at the surface of bioactive sol−gel derived 3D glass scaffolds via a complete PIXE characterization were studied. 3D glass foams in the SiO₂−CaO system were prepared by sol−gel route. Samples of glass scaffolds were soaked in biological fluids for periods up to 2 days. The surface changes were characterized using particle induced X-ray emission (PIXE) associated to Rutherford backscattering spectroscopy (RBS), which are efficient methods to perform quantitative chemical maps. Elemental maps of major and trace elements at the glass/biological fluids interface were obtained at the micrometer scale for every interaction time. Results revealed interconnected macropores and physicochemical reactions occurring at the surface of pores. The micro-PIXE-RBS characterization of the pores/biological fluids interface shows the glass dissolution and the rapid formation of a Ca rich layer with the presence of phosphorus that came from biological fluids. After 2 days, a calcium phosphate-rich layer containing magnesium is formed at the surface of the glass scaffolds. We demonstrate that quantities of phosphorus provided only by the biological medium have a significant impact on the development and the formation of the phosphocalcic layer.

The aim of this study is to highlight the influence of magnesium doping on the surface reactivity of binary (SiO₂–CaO) and ternary (SiO₂–CaO–P₂O₅) bioactive glasses, prepared by sol–gel chemistry, in biological conditions. These materials were produced in powder form, and their compositional and textural properties characterized. They were then soaked in biological fluids for different delays from 0 to 4 days. The surface changes were characterized using Particles Induced X-ray Emission (PIXE) associated with Rutherford Backscattering Spectroscopy (RBS), which are efficient methods for multi-elemental analysis. Elemental maps of major and trace elements were obtained at a micrometer scale and revealed the formation of a calcium phosphate-rich layer after a few days of interaction. We demonstrate that the presence of magnesium in the material has an impact on the development and the formation rate of the bone-like apatite layer.

The 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. The two most commonly used materials shapes for clinical applications – glass particles and glass bulk – were studied and provide us with concordant results. 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 the treatment of osteoporosis and tissue engineering.

The prerequisite for bioactive glasses to bond to living bone is the formation of biologically active apatites on their surface in the body. Reactions and bioactivity mechanisms between bioactive glasses and bone depend on the glass composition. We study a glass in the SiO₂‐Na₂O‐CaO‐P₂O₅‐K₂O‐Al₂O₃‐MgO system. To characterise physicochemical reactions at the materials periphery, we immersed the glass pastilles into biological fluids for periods of 5, 10, and 20 days. The surface changes were studied at the micrometer scale by a Particle Induced X‐ray Emission (PIXE) method associated with Rutherford Backscattering Spectroscopy (RBS). After 20 days of immersion, elemental maps showed the formation of a calcium‐phosphate layer at the surface of the glass pastilles. The thickness of this layer was around 15 µm. Thanks to the PIXE method, we demonstrated the presence of traces of Mg in this layer. The glass doped with MgO leads to the formation of an apatite which incorporates magnesium. Formation of this Ca‐P‐Mg layer represents the bioactive properties of the studied glass. This biologically active layer improves the properties of the glass and will permit a chemical bond between the ceramic and bone.

Numerous studies have described the bioactive properties of glass particles in the SiO₂‐CaO‐Na₂O‐P₂O₅ system. This kind of material is capable of developing a direct contact with bone through dissolution and physicochemical reactions. We have investigated the influence of bioactive particles, and ionic products from the same particles, on the intracellular concentrations in monocyte cells, which are among the first cells to colonize implantation sites. The only way to access these concentrations and particularly diffusible ionic concentrations (potassium, sodium, and chlorine) is to use cryomethods coupled to electron probe microanalysis. We have paid particular attention to the potassium:sodium ratio, the most sensitive criterion of viability. We have cultured cells with bioactive glass particles and in a conditioned medium obtained from the dissolution of the glass particles in the standard medium. Our study demonstrates that cells cultured in a conditioned medium are more active than cells cultured in a standard medium, or cells exposed to bioactive particles, and particles are more toxic for cells than are ionic products. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 65A: 441–446, 2003