Mixed alkali effects in Bioglass® 45S5

Bioactive glasses, particularly Bioglass (R) 45S5, have been used to clinically regenerate human bone since the mid-1980s; however, their high crystallisation tendency still limits their range of applications. In order to develop new bioactive glass compositions, which combine high bioactivity with good processing of the melt, a deeper understanding of the role of modifier oxides on the structure and thermal properties of the glasses is required. Here, the influence of different alkali cations, Li2O, Na2O and K2O, on the properties of Bioglass (R) 45S5 has been investigated. Potassium cations expanded the silicate network, making it less compact, and thereby lowered hardness and Young's modulus. Lithium cations, on the other hand, made the silicate network more compact, which increased both hardness and Young's modulus. Structural analyses suggest non-random partitioning of modifier cations between the silicate and orthophosphate phase in mixed-alkali compositions. Transition and crystallisation temperatures of glasses containing two alkali cations showed the typical mixed alkali effect, with temperatures being lower than those of glasses containing one alkali cation only. Substitution of Na for Li or K resulted in an increased processing window (temperature range between T-9 and the onset of crystallisation) with the exception of the fully substituted potassium glass, which had the smallest processing window of all glasses. Taken together, these results suggest that bioactive glasses in which sodium is partially substituted (particularly with potassium) are of great interest to improve the processing, making the glasses more suitable for sintering or fibre drawing applications. (c) 2013 Elsevier B.V. All rights reserved.