Effect of bioactive glass crystallization on the conformation and bioactivity of adsorbed proteins

Protein adsorption onto the surface of a biomaterial mediates cell adhesion and enhances tissue-implant integration. In a previous study, we demonstrated that crystallization of bioactive glass (BG) significantly increased the negative zeta potential and decreased serum protein adsorption onto the material surface. In this study, the conformation of protein adsorbed onto the surface of amorphous bioactive glass (ABG) and crystallized bioactive glass (CBG) was analyzed and correlated to bone marrow mesenchymal stem cell adhesion and spreading. ABG and CBG were immersed in three different protein solutions containing 10% fetal bovine serum, bovine serum albumin (BSA), and fibronectin (FN) for 4 h at 37 degrees C. Grazing angle Fourier transform infrared spectroscopy (GA-FTIR) demonstrated that the ratio of (amide I)/(amide II) functional groups of all proteins adsorbed onto ABG was greater than that for proteins adsorbed onto CBG. The Gaussian curve fitting analysis suggests that the significant expression of amide I, rich in charged and flexible unordered secondary structure of adsorbed FN, stimulated bone cell adhesion and spreading on the surface of ABG. CBG enforces protein conformation that exposes amide II, rich in neutral and stable beta-sheet structure and alpha-helix, which limited cell adhesion and spreading. Although ABG adsorbed significantly higher quantity of BSA than FN, GA-FTIR analyses showed that the ratio of amide I/amide II was significantly higher for adsorbed FN. Therefore, the intensity of amide I or amide II bands cannot be taken as a measure of the quantity of adsorbed protein.