Structural characterization of bioactive glasses

Abstract

Several bioactivematerials have been studied in the last decades for many applications in medicine [1,2]. We will focus our attention on bioactive glasses, which represent the first class of inorganic materials, which showed the peculiar surface property of bonding to living bone. When a bioactive glass is soaked in a fluidmimicking the inorganic composition of human plasma (simulated body fluid, SBF) several surface reactions can occur, leading, by a complex mechanism including ion leaching, silica gel formation, Ca and PO4 3diffusion, to the precipitation of hydroxy-carbonate apatite (HCA) with composition and structure close to the mineral phase of bone. The precipitation of HCA on bioactive glasses has been extensively investigated [2], but information on the structural features of the HCA film, especially in the early stages of deposition, is still lacking. Bioactive glasses can be massive or porous to host drugs to be delivered after prosthesis insertion. We present here the characterization of different kinds of glasses (both massive and porous) for applications in orthopedic and dental devices, to shed some light on the growth mechanism of: i) HCA on massive SCK (silica, Ca and K) bioactive glass plates and ii) an ordered mesoporous SBA phase inside porous SCK bioactive glass scaffolds. Synchrotron radiation GIWAXS measurements were carried out on plates ofmassive SCK glass, soaked in SBF for increasing times. Initially the scattering curves only show the presence of an amorphous phase, due to the glass itself, but the presence of a new crystalline phase is already evident after 15 h soaking. This diffraction profile due to a crystalline phase increases with the soaking time and after 15 days it is possible to identify the full pattern of HCA present on the surface of the SCK bioactive glass. The deposition of an ordered silica mesophase inside the macroporous structure of a SCK bioactive glass scaffold allows to combine the bioactivity of the latter with the drug delivery properties of the ordered mesoporous systems [3]. The X-ray diffraction patterns of the SCK (scaffold)-SBA composite materials clearly indicate the presence of peaks with d-spacings consistent with the presence of a hexagonal SBAmaterial. The collected diffraction patterns show that the crystallinity of the SBAphase depends on the aging conditions and our data suggest that the ageing at 60 °C for 72 h is more efficient in obtaining an ordered SBA layer.