Apatite formation of bioactive glasses is enhanced by low additions of fluoride but delayed in the presence of serum proteins

• Low concentrations of fluoride enhance apatite formation in bioactive glasses.
• Serum proteins delay apatite precipitation with minimal effect on ion release.
• Ion concentrations remain high at later time points in serum-containing media.

Five bioactive glass compositions in the SiO2–P2O5–CaO–Na2O–CaF2 system (0–32 mol% CaF2) and Bioglass® 45S5 were evaluated for their apatite forming ability in serum-free and serum-containing cell culture media for up to seven days. While F− ions in low concentrations were found to enhance apatite formation, higher fluoride content caused formation of fluorite and calcite. The presence of serum proteins delayed apatite precipitation for all compositions, while Bioglass® 45S5, despite considerably higher phosphate content (2.6 vs. ≤1.1 mol% P2O5) and high concentrations of Ca2+ and PO43− in solution, formed only amorphous calcium phosphate.