Aluminosilicate Glasses As Yttrium Vectors for in situ Radiotherapy: Understanding Composition-Durability Effects through Molecular Dynamics Simulations

The use of yttrium aluminosilicate (YAS) glasses as vectors for radiotherapy is critically affected by the glass durability in a physiological medium. To understand the relation between glass composition, structure, and durability at an atomistic level, we have carried out classical molecular dynamics (MD) simulations of two YAS compositions with different durability. The analysis of the MD trajectories shows that the lower durability at high Y 2 O 3 concentration is due to the combined effect of lower connectivity of the glass network and reduced yttrium clustering. Increasing the yttrium content increased the coordination numbers of all atomic species, made possible a greater range of atomic environments, and reduced the network connectivity, particularly related to silicon. Aluminum ions show a strong tendency to self-aggregate, and can form additional Al−O−Al linkages to balance the reduced number of Si network-formers in the high Y 2 O 3 composition: this leads to some very highly connected aluminum atoms, characterized by the appearance of large- n Q n (Al) species in the corresponding distribution. The presence of significant yttrium clustering only in the more durable, low Y 2 O 3 composition denotes that clustering of modifier ions can further enhance the glass durability, in agreement with previous results for bioactive glasses. (Tilocca et al. Chem. Mater. 2007, 19, 95.)