Evaluation of Modified Fluorcanasite Glass-Ceramics for Hard Tissue Replacement

Objectives: Fluorcanasite glass-ceramics have a highly crystalline microstructure and excellent mechanical properties. Recently Miller et al. demonstrated that the addition of excess CaO and P2O5 to the stoichiometric composition induced the formation of an apatite layer in simulated body fluid, demonstrating improved biocompatibility and osteoconductive potential. No quantitative data regarding their biocompatibility has been published, and knowledge of structure-property relationships in these materials remains limited. The aim of this study was therefore to further characterise these modified fluorcanasite glass-ceramics and to quantify their in vitro biocompatibility using established methods. Methods: Glasses and the glass-ceramics prepared using controlled two stage heat-treatments were characterised using X-Ray Fluorescence Spectrometry (XRF), Differential Thermal Analysis (DTA), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). In vitro biocompatibility was investigated using rat osteosarcoma cells (ROS 17/2.8, Merck Inc., USA) with a quantitative MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Ion release from discs (12 mm diameter x 2 mm thickness) was determined using inductively couple plasma-mass spectrometry (ICP-MS). Results: XRF data showed a close similarity between the pre-melt and post-melt molar compositions. The DTA curves of glasses showed exothermic peaks that were assigned to the crystallisation of various phases, identified by XRD. Essentially Glass 1, 2 and 3 crystallised at 520°C/2h and 780°C/2h to form frankamenite (Glass 1), frankamenite, fluorcanasite, xonotlite (Glass 2) and frankamenite, fluorcanasite, xonotlite, and fluorapatite (Glass 3). The SEM microstructures obtained from fractured surfaces of the glass-ceramics consist of interlocking crystals of the strengthening chain silicate phase. Quantitative MTT assay results were in good agreement with the qualitative SEM observations reported previously. The ion release data suggested a close relationship between solubility (in particular sodium release) and biocompatibility. Conclusion: Reduced solubility and related pH effects appeared to be the principal mechanism responsible for the improvement in in vitro biocompatibility reported here for these novel glass-ceramics.