Mapping the elemental and crystalline phase distribution in Cu2+doped 45S5 bioactive glass upon crystallization

Bioactive glasses (BGs) incorporating metallic ions to impart antibacterial activity and stimulation of osteogenesis and angiogenesis are promising candidates for bone tissue engineering. Silicate BGs of the 45S5 composition (45 SiO2, 24.5 Na2O, 24.5 CaO, 6 P2O5, (wt%)) crystallize readily during the high temperature processing of porous scaffolds. The crystallization slightly suppresses the bioactivity and dissolution of the glass. Structural changes during the high-temperature processing of metal ion-doped 45S5 BGs are challenging since metal ions may affect the formation of crystalline phases during thermal treatment. In this study, we investigated the effect of Cu on structural changes during the sintering of Cu doped 45S5 BG (Cu-45S5). The Cu-45S5 BG was sintered at 900 °C and 1050 °C for 1 hour, and the resultant microstructures were investigated using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), including elemental distribution mappings from energy-dispersive X-ray spectroscopy (EDXS), and X-ray nano-computed tomography (nano-CT). XRD patterns of thermally treated samples indicate the formation of combeite and rhenanite as crystalline phases. Besides the crystalline fraction, a residual glassy phase is also present, which is enriched with Na and P ions. The results reveal that the crystallinity of Cu-45S5 glass-ceramics can be adjusted over a range of 70-78% by applying appropriate heat treatment profiles. Moreover, the size of the crystals increases with increasing temperature under the investigated conditions. Cu is found to be localized in the residual glassy phase, together with Si and Na, which has an effect on the release of Cu ions in physiological environments.