Medium-range order in phosphosilicate bioactive glasses: Insights from MAS-NMR spectra, chemical durability experiments and molecular dynamics simulations

The medium-range order of phospho-silicate bioactive glasses (with compositions (2 p)SiO2 Æ 1Na2O Æ 1.1CaO Æ pP2O5, in whichp = 0.10, 0.20, 0.26) has been studied by means of a combined-experimental (MAS-NMR, chemical durability measurements) and computational(classical molecular dynamics (MD)) approach. The structural model obtained by MD is showed to be helpful in the interpretationof the NMR spectra. A small amount of Si–O–P link units has been detected in glasses with low P2O5-content, but at high P2O5concentration the percentage of Si–O–P bridges becomes important. However, Qn distributions show that the HP5 (p = 0.20) glass structureis less polymerized with respect to the H (p = 0.10) and HP6.5 (p = 0.26) glasses. These results provide useful explanation of thebehavior of these glasses in water and highlight the influence of the medium-range order on a very important property of potentialbioactive glasses such as the chemical durability.