THE EFFECT OF IN-VITRO MODELING CONDITIONS ON THE SURFACE-REACTIONS OF BIOACTIVE GLASS

Using one parametric variation in solution composition, this paper doc uments that the surface reactions on bioactive glass (BG) 45S5 are exq uisitely dependent upon the modeling conditions. The solutions used we re 0.05M tris hydroxymethyl aminomethane/HCl (tris buffer), tris buffe r complemented with plasma electrolyte and/or serum, and serum. The re acted surfaces were analyzed using Fourier transform infrared (FTIR), scanning electron microscopy (SEM) with energy dispersive X-ray analys is (EDXA), and Rutherford backscattering spectroscopy (RBS). Post-imme rsion solutions were analyzed for changes in Ca and PO4 concentrations . After a short immersion (3 h), a crystalline, carbonated hydroxyapat ite (c-HA) layer formed only in tris. Reaction surfaces of different s tructure, morphology, and composition were observed after various shor t and longer term immersions in all other solutions. They comprised tw o layers with the layer in contact with the bulk consisting mainly of Si; the outer layer, composed of Si, Ca, and P, was amorphous, and had a Ca/P ratio of about 1. Serum proteins adsorbed on the BG surfaces a t the early stages of the solution-mediated BG reactions. Formation of a crystalline c-HA layer was delayed up to three or more days in solu tion with plasma ions. In the presence of serum, only amorphous surfac es composed of Si, Ca, and P were observed for any time up to seven da ys of immersion. The present data suggest that serum proteins adsorb i n tandem with the occurrence of solution-mediated reactions leading to formation of a silica-gel. Amorphous Ca-P phases accumulate in the Si -rich matrix. Furthermore, the present data, in conjunction with the d ata published before,(1) suggest that physicochemical and cell-mediate d reactions occur in parallel to form the glass-tissue interfacial lay er. (C) 1997 John Wiley & Sons, Inc.