Dissolution and scanning electron microscopic studies of Ca,P particle-containing bioactive glasses

Area of Science:

• Biomaterials Science
• Materials Chemistry
• Surface Science

Background:

• Bioactive glasses are known for their ability to form a hydroxyapatite layer in simulated body fluid (SBF).
• Incorporating calcium phosphate (Ca,P) phases like hydroxylapatite or rhenanite into bioactive glasses may alter their surface reactivity and precipitation behavior.

Purpose of the Study:

• To investigate and compare the in vitro calcium phosphate (Ca,P) precipitation behavior of bioactive glasses and their composites with hydroxylapatite and rhenanite.
• To understand the influence of material composition and phases on the precipitation mechanism and kinetics.

Main Methods:

• Materials tested: two bioactive glasses and four composites (two with hydroxylapatite, two with rhenanite).
• Exposure to simulated body fluid (SBF) and Tris-Buffer at various time points (3-144 h).
• Analysis techniques: weight loss measurements, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), atomic absorption spectroscopy, spectrophotometry, and pH measurements.

Main Results:

• Composite materials exhibited a higher capacity for Ca,P precipitation than the parent glasses.
• Weight loss correlated well with material composition.
• Precipitation initiated preferably from the glass phase and was influenced by Ca,P particles, affecting onset time and rate.
• Absence of a clear Si-rich layer in some composites was attributed to the presence of excess Ca and P ions.

Conclusions:

• Bioactive glass composites demonstrate superior in vitro Ca,P precipitation capabilities compared to glasses alone.
• The interplay between the glass and Ca,P phases critically governs the precipitation process.
• An Si,Ca,Na film formation appears to be an initial step in the Ca,P precipitation mechanism on these materials.