Fluorine environment in bioactive glasses: ab initio molecular dynamics simulations

Area of Science:

• Materials Science
• Biomaterials
• Computational Chemistry

Background:

• Fluorinated bioactive glasses (FBGs) offer combined antibacterial and bioactive properties.
• Understanding the fluorine environment is crucial for FBGs' biomedical applications.
• Previous studies lacked detailed atomic-level insights into fluorine's role.

Purpose of the Study:

• To elucidate the atomic structure and bonding environment of fluorine in a 45S5 Bioglass composition modified with CaF(2).
• To investigate the structural role of fluorine and its interactions with glass network formers and modifiers.
• To resolve long-standing questions regarding fluorine coordination in bioactive glasses.

Main Methods:

• Car-Parrinello molecular dynamics (CPMD) simulations were employed.
• A 45S5 Bioglass composition with 10 mol% CaO replaced by CaF(2) was simulated.
• Analysis focused on fluorine coordination and bonding within the glass structure.

Main Results:

• Fluorine is predominantly coordinated to modifier ions (Na and Ca) in a mixed state.
• A very small fraction of Si-F bonds were observed, mainly at high temperatures or in the melt precursor.
• Formation of Si-F bonds involving expanded coordination shells (tetra- and penta-coordinated silicon) is disfavored.

Conclusions:

• Fluorine's primary interaction is with modifier ions, not the silicate network.
• The bonding environment of fluorine significantly influences the properties of FBGs.
• These findings provide a fundamental understanding for designing advanced fluorinated bioactive glasses.