Initial events at the bioactive glass surface in contact with protein-containing solutions

Upon implantation, bioactive glass undergoes a series of reactions that leads to the formation of a calcium phosphate-rich layer. Most in vitro studies of the changes that occur on the surface of bioactive glass have employed the use of buffer solutions with compositions reflecting the ionic composition of interstitial fluid. Although these studies have documented the physical and chemical changes associated with bioactive glass immersed in aqueous media, they do not reveal the effect of serum proteins and cells that are present at the implantation site. In the present study, we document, using atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS), significant differences in the reaction layer composition, thickness, morphology, and kinetics of formation arising from the presence of serum proteins. The data reveal that the uniform and rapid adsorption of serum proteins on the surface may serve to protect the surface from further direct interaction with the aqueous media, slowing down the transformation reactions. This finding is in agreement with previous studies that have shown that the presence of serum proteins significantly delays the formation of hydroxyapatite at the surface of bioactive glass. These data also support the hypothesis that initial reaction layers in vivo interact with cells in order to produce the tissue-bioactive glass interface typically observed on ex vivo specimens.