Analysis of γ-irradiated synthetic bone grafts by ²⁹Si MAS-NMR spectroscopy, calorimetry and XRD

Ca-Sr-Zn-Si glasses have demonstrated excellent biocompatibility both in vitro using the MTT assay with L929 mouse fibroblast cells, and in vivo using healthy and ovariectomized female Wistar rats. However, the biological evaluation of the materials was performed on glass granules that were autoclaved, rather than γ-irradiated; the sterilisation procedure required prior to implantation of these materials in the human body. Given the fact that when a glass is exposed to ionizing radiation changes in its physical properties can take place, it is imperative to determine whether the structure of such glasses will be altered as a result of exposure to the typical amounts of γ-irradiation required to sterilise such materials prior to implantation. This paper examines the structure of Na-Ca-Sr-Zn-Si glasses using ²⁹Si MAS-NMR, XRD and DTA and to evaluate the effect of 30 kGy γ-irradiation on their structure. The ²⁹Si MAS-NMR results indicate that the peak maxima for each glass remains between -74 ppm and -79 ppm; a chemical shift for ²⁹Si associated with Q¹ units in silicate glasses, and that the local environment around the ²⁹Si isotope remains unaltered as a result of exposure. Additional analysis (DTA and XRD) showed that the onset of the glass transition temperature, T_g (in the range 553 °C-619 °C depending on composition) typically remains unchanged, as a result of exposure to the ionizing radiation, as do the XRD diffractograms for each glass. Therefore it can be concluded that the use of 30 kGy γ-irradiation does not effect the local environment of the ²⁹Si isotope in the glasses, nor does it significantly alter the XRD diffraction patterns or the T_g values for CaO-SrO-NaO-ZnO-SiO₂ described in this work.