Carbonate hydroxyapatite gel monolith formation and drying

Area of Science:

• Materials Science
• Ceramics Engineering
• Biomaterials

Background:

• Carbonate incorporation reduces hydroxyapatite crystal size, a property previously unexplored for gel monolith fabrication.
• Fabricating crack-free carbonate hydroxyapatite ceramics requires controlled gel monolith preparation.

Purpose of the Study:

• To devise a repeatable method for producing crack-free carbonate hydroxyapatite gel monoliths.
• To investigate the effect of carbonate content on gelation and pore structure.

Main Methods:

• Precipitation reaction to prepare carbonate hydroxyapatites (5.8 and 7.8 wt% carbonate).
• Biaxial vacuum filtration for disc-shaped monolith formation.
• Slow air drying and characterization of gelation kinetics and physical properties.
• Mercury porosimetry for pore size distribution analysis.

Main Results:

• Intact monoliths up to 9.9 g were successfully formed.
• Gelation behavior was independent of monolith size and carbonate content.
• Gel monoliths exhibited a monomodal pore size distribution (mean 9.1 nm), unlike commercial hydroxyapatite's bimodal distribution.
• Final green density of all monoliths was 37%, with gelation occurring at 50-55 vol% water.

Conclusions:

• A repeatable method for crack-free carbonate hydroxyapatite gel monolith fabrication was established.
• The method allows for controlled production of ceramics with tailored pore structures.
• Carbonate-induced crystal size reduction is key to this novel fabrication approach.