Ga-Modified (Si-Ca-P) Sol-Gel Glasses: Possible Relationships Between Surface Chemical Properties and Bioactivity

In vitro bioactivity features of a Ga-modified sol gel Si-Ca-P glass(SGGa) were investigated, in comparison with a plain ternary Si-Ca-P system(SG). Reaction/dissolution of the glass at increasing soaking times in simulatedbody fluids (SBF) and the consequent growth of an apatite-like layer, monitoringbioactivity, were studied by employing a variety of chemical and physical techniques.The growth of a crystalline apatitic layer at the Ga-modified-glass/SBFinterface is severely delayed with respect to the Ga-free glass, and the reasons for ithave been looked for in the dramatic changes induced, at the glass/SBF interface, bythe presence of the Ga2O3 component. In situ Fourier transform infraredspectroscopy allowed to describe the nature/structure of surface terminations forthe two glasses and to reveal/quantify the acidic strength of different Ga speciesexposed at the SGGa glass surface. 2,6-Dimethylpyridine and carbon monoxidewere employed as molecular probes to reveal Brønsted and Lewis acidity. At thesurface of the Ga-modified glass, both Brønsted and strong Lewis acidic sites are present. The enhanced surface acitiy of SGGa glass,with respect to the plain glass SG, has been proposed to be responsible for the slower glass dissolution in SBF and for the delayeddeposition/crystallization of an apatite-like layer at the glass/SBF interface.