Assessing the phosphate distribution in bioactive phosphosilicate glasses by 31P solid-state NMR and molecular...

Area of Science:

• Materials Science
• Biomaterials Engineering
• Solid-State Chemistry

Background:

• Melt-derived phosphosilicate glasses are key bone-grafting materials in surgery.
• Understanding medium-range structural features (up to ~1 nm) of these glasses is limited.
• Phosphate group distribution significantly impacts glass bioactivity.

Purpose of the Study:

• To comprehensively assess the spatial distribution of phosphate groups in Na2O-CaO-SiO2-P2O5 glasses.
• To investigate the influence of phosphate content and silicate network connectivity on phosphate distribution.
• To correlate structural insights with glass bioactivity.

Main Methods:

• Employed double-quantum (31)P nuclear magnetic resonance (NMR) spectroscopy under magic-angle spinning (MAS).
• Utilized molecular dynamics (MD) simulations to model glass structures.
• Evaluated MD models against random and clustered phosphate group distribution scenarios.

Main Results:

• Phosphate atom distribution in phosphosilicate glasses is well-approximated by a statistical (random) distribution, particularly within 450 pm.
• MD-derived structures showed slightly closer P-P interatomic contacts (450-600 pm) than purely random distributions.
• Phosphate ion dispersion was largely independent of silicate network polymerization and P content (1-6 mol % P2O5).

Conclusions:

• The spatial arrangement of phosphate groups in these glasses is predominantly random.
• This finding provides critical insights into the structure-property relationships of bioactive phosphosilicate glasses.
• The results aid in the rational design of improved bone-grafting materials.