The role of the thickness and the substrate on the in vitro bioactivity of silica-based glass coatings

The in vitro behaviour of bioactive glass coatings grown by Pulsed Laser Deposition on silicon and titanium substrates is presented. The critical thickness of the coatings needed to develop the complete bioactive reactions when immersed in Simulated Body Fluid was evaluated. The influence of the substrate on the reactivity of thin coatings, which lead to the production of calcium phosphate and silica-rich layers, is discussed. Furthermore, the temporal evolution of the bioactivity process was followed for thick bioactive glass coatings deposited on biomorphic silicon carbide ceramics. In the in vitro tests of coated porous materials, the surface area to volume of Simulated Body Fluid ratio was revealed as a key parameter. The effective surface area should be carefully estimated in order to avoid adverse effects on the bioactive process.