Micro-ion beam analysis of physico-chemical reactions in vitro induced by nanostructured sol-gel derived bioactive glasses
Caractérisation par micro-faisceau d'ions des réactions physico-chimiques induites in vitro par des verres bioactifs nanostructurés élaborés par la méthode sol-gel
Résumé
The study of bioactive glasses is a multi-field area of research aiming at a major goal: the development of new generation biomaterials that would be able to bond with host tissues through the formation of a strong interfacial bond, together with helping the body heal itself through the stimulation of specific cellular responses. Thus clinical applications of bioactive glasses mainly concern dental surgery and orthopaedics, for filling osseous defects. For this purpose, we have elaborated bioactive glasses in the binary SiO2-CaO system, ternary SiO2-CaO-P2O5 system, and for the first time, to our knowledge, strontium-doped SiO2-CaO-SrO and SiO2-CaO-P2O5-SrO glasses. The materials were elaborated using the sol-gel process, which allowed the synthesis of nanoporous materials with great purity and homogeneity. The bioactivity of the glasses was clearly demonstrated in vitro: in contact with biological fluids, the whole lot of materials were able to induce the formation of a Ca-P-Mg layer a few microns thick at their surface. Our work is characterized by the use of PIXE-RBS nuclear microprobes to study the bioactive glass/biological fluids interface. Thanks to these methods we obtained chemical maps that made possible the analysis of major and trace elements concentrations at the interface. Moreover, quantitative information regarding the local reactivity of glasses were acquired. These data are important to evaluate the kinetics and amplitude of the physico-chemical reactions involved in the bioactivity process. Thus, we highlighted that the binary glass is the highest reactive regarding the dissolution of the glassy matrix as well as the first appearance of the Ca-P rich layer. However the Ca/P atomic ratio calculated at the glass/biological fluids interface decreases slowly, indicating that the Ca-P-Mg layer encounters difficulties to be changed into a more stable apatitic phase. For the P-containing glasses, the dealkalinization of the matrix and the formation of the calcium phosphate layer are delayed. However, calculation of the interfacial Ca/P ratios along with supersaturation studies of the biological medium demonstrate that the Ca-P-Mg layer is quickly changed into an apatitic phase. Concerning the Sr-doped glasses, we highlighted that the dissolution of the material decreased and that the Ca-P-Mg layer was formed on a reduced depth. Nevertheless, according to the rapid decrease of the Ca/P ratio, there is evidence that the layer is more quickly changed into apatite. We also demonstrated that traces of Sr are both present at the glass/biological fluids interface and diffused in the biological medium. Knowing the positive effects of Sr on the cellular activity and on the bone modelling process, it might result in an improved bioactivity for the Sr-doped glasses in contact with a living system.
Les verres bioactifs permettent de combler les défauts osseux lors d'applications cliniques. Nous avons élaboré par sol-gel plusieurs verres bioactifs, parmi lesquels des verres dopés en Sr. La bioactivité des verres est avérée : au contact d'un milieu biologique, une couche Ca-P se forme rapidement en surface de nos matériaux. La caractérisation de l'interface verre/ milieu biologique par faisceau d'ions démontre que le verre binaire est le plus rapide en ce qui concerne la dissolution de la matrice et l'apparition de la couche Ca-P. Pour les verres contenant du P, ces phénomènes sont retardés, mais la couche Ca-P-Mg se développe vite en une couche apatitique. Pour les verres dopées en Sr, la couche Ca-P-Mg se forme sur une profondeur réduite. Néanmoins elle évolue plus vite en apatite. De plus la présence de Sr à l'interface verre/ liquide et dans le milieu biologique pourrait résulter, grâce aux effets bénéfiques du Sr sur l'activité cellulaire, en une bioactivité améliorée in vivo