Bioactive glass–ceramics containing fluorapatite, xonotlite, cuspidine and wollastonite form apatite faster than their corresponding glasses

Abstract

Crystallisation of bioactive glasses has been claimed to negatively affect the ion release from bioactive glasses. Here, we compare ion release and mineralisation in Tris–HCl buffer solution for a series of glass–ceramics and their parent glasses in the system SiO2–CaO–P2O5–CaF2. Time-resolved X-ray diffraction analysis of glass–ceramic degradation, including quantification of crystal fractions by full pattern refinement, show that the glass–ceramics precipitated apatite faster than the corresponding glasses, in agreement with faster ion release from the glass–ceramics. Imaging by transmission electron microscopy and X-ray nano-computed tomography suggest that this accelerated degradation may be caused by the presence of nano-sized channels along the internal crystal/glassy matrix interfaces. In addition, the presence of crystalline fluorapatite in the glass–ceramics facilitated apatite nucleation and crystallisation during immersion. These results suggest that the popular view of bioactive glass crystallisation being a disadvantage for degradation, apatite formation and, subsequently, bioactivity may depend on the actual system study and, thus, has to be reconsidered.

Phosphate/Silicate Ratio Allows for Fine-Tuning of Bioactive Glass Crystallisation and Glass-Ceramic Microstructure

“…Glasses here also contain fluoride (as calcium fluoride) to allow for crystallisation of fluorapatite as an apatite crystal phase [28]. (Details on network connectivity in this system are given in our previous publication [25]. )…”

“…Therefore, the present work aims to investigate the crystallisation mechanism (e.g., volume or surface crystallisation) of glasses in the system SiO 2-P2O5-CaO-CaF2 and to establish the relationship between phosphate/silicate ratio, thermal behaviour and glassceramic microstructure such as crystal composition, crystalline fraction, and crystal size and morphology. As the presence of apatite crystals within a bioactive glass matrix is known to influence ion release and apatite precipitation during contact with physiological solutions, this has been investigated in a separate study [25].…”