Bioactive glasses

This chapter reviews the use of computer simulation of bioactive silicate-based glasses in order to understand how the glass composition and structure affects the bioactivity. Key to this is the successful modeling of the interatomic forces, which is often done through the use of classical empirical expressions (potentials) to allow for simulations larger in length and time than could be done from first principles. The inclusion of polarizability into these potentials is crucial to represent the Q ⁿ distribution and medium-range structure accurately, which both strongly affect the bioactivity of the glass. Results obtained with such potentials are in good agreement with experimental data and first-principles simulations. Silicon and phosphorous are network formers; sodium and calcium are network modifiers, which compete for nonbridging oxygen (NBO) atoms and the amounts of NBOs in the first coordination shell of each cation correlates with its field strength. Local chemical bonding can also drive clustering on larger length scales, which can lead to structural inhomogeneities which could affect the bioactivity. By appropriate fitting of the potentials, the effect on including other therapeutic ions can be considered, including, in some cases, ions which exist in more than one oxidation state in the glass. The changes in the structure present at the surface of the glass after implantation in the body are also accessible to computer simulation, although it can be difficult, using current techniques, to understand completely the chemical reactions between the glass and the surrounding environment. Future directions for research are also discussed.