Structure and dissolution of silicophosphate glass

Area of Science:

• Materials Science
• Solid State Chemistry
• Biomaterials

Background:

• Phosphate-silicate glasses containing sodium and calcium oxides are explored for therapeutic ion-releasing applications.
• Understanding the structural role of silicon is crucial for tailoring glass properties.

Purpose of the Study:

• To investigate the coordination state of silicon (Si) in P₂O₅-SiO₂-Na₂O-CaO glasses.
• To correlate the structure, particularly the presence of six-fold-coordinated silicon (^[6]Si), with glass dissolution behavior.

Main Methods:

• Classical molecular dynamics simulations and first-principles calculations were used to model glass structure.
• Experimental glass preparation involved substituting sodium oxide (Na₂O) with calcium oxide (CaO).
• ³¹P and ²⁹Si magic-angle-spinning-nuclear-magnetic-resonance (MAS-NMR) spectroscopy characterized the glass structure.
• Dissolution tests were performed in a tris-HCl buffer at 37 °C.

Main Results:

• The model predicted that phosphorus (P) induces ^[6]Si formation by elongating Si-O bonds, with ^[6]Si acting as a network former.
• ^[6]Si preferentially coordinated with phosphate tetrahedra (Q _P ³).
• Experimental results showed an increase in Q _P ³ and ^[6]Si with increasing Na₂O content.
• Glass dissolution rates were suppressed by the coexistence of CaO and Na₂O.

Conclusions:

• The formation of ^[6]Si, influenced by P and stabilized by Na⁺, plays a key role in the glass network.
• The reduced hydrolysis due to electron delocalization in ^[6]Si-coordinated Q _P ³ units contributes to suppressed ion dissolution.
• These findings highlight the potential of P₂O₅-SiO₂-Na₂O-CaO glasses as stable therapeutic ion-releasing materials.