Effect of CeO2 doping on thermal, optical, structural and in vitro properties of a phosphate based bioactive glass

In this paper, we investigate the effect of CeO2 doping on the thermal, structural, optical and on the in vitro properties of a bioactive phosphate glass. The aim is to verify that luminescent ions such as Ce ions may be beneficial for tissue healing, and also serve as markers to the glass dissolution. Also important is to ensure that the addition of Ce does not reduce the glass resistance to crystallization and thus its ability to be shaped into scaffold or drawn into fiber. The glass composition was x CeO2 - (100 - x) (0.5 P2O5-0.2 CaO-0.2 SrO-0.1 Na2O) with x varying from 1 to 7.5 mol%. Ce ions were present in the glass most likely as Ce3+ and Ce4+, as evidenced by the Ce3+ luminescence. An increase in CeO2 content led to an increase in concentration of Ce4+ ions, giving the glass a yellow-gold coloration and an increase in non-radiative energy transfer between Ce3+ ions. CeO2 doping induced a higher degree of cross-linking as evidenced by the increase in Q(1) units at the expense of the Q(2) units in the glass structure. This increase in cross-linking gave rise to glasses with higher chemical durability. When immersed in SBF for up to one week the undoped glass shows significant reaction and formed a Sr-substituted calcium phosphate layer. When the CeO2 content was increased the formation of the layer was slower leading to a thinner layer. Small Ce amounts were identified in the layer formed at the surface of the glasses x = 1 and x = 2.5 and in all cases Ce was not detected in the solution. Finally, a decrease in the Ce3+ luminescence was measured with increasing immersion time. This decrease could be attributed to the layer formation and/or the oxidation of Ce3+ into Ce4+ when incorporated into the Sr-CaP layer. This study demonstrates that Ce ions can potentially be used as a marker to the glass dissolution. (C) 2014 Elsevier B.V. All rights reserved.