Enhanced osteoconductivity of sodium-substituted hydroxyapatite by system instability

Area of Science:

• Biomaterials Science
• Materials Chemistry
• Skeletal Biology

Background:

• Hydroxyapatite is a key component of bone, but its osteoconductivity can be limited.
• Modifying hydroxyapatite's structure may enhance its bone regeneration capabilities.
• Investigating ion substitution offers a route to tune biomaterial properties.

Purpose of the Study:

• To investigate the effect of sodium substitution for calcium on hydroxyapatite's osteoconductivity.
• To synthesize and characterize sodium-substituted hydroxyapatite (Na-HA).
• To evaluate the in vitro and in vivo performance of Na-HA compared to pure hydroxyapatite (HA).

Main Methods:

• Synthesis of Na-HA and HA via precipitation and sintering.
• Characterization of structural defects using ab initio calculations.
• In vitro dissolution studies in simulated body fluid (SBF) and Tris-buffered water.
• In vivo implantation in rabbit calvarial defects and assessment of osteoconductivity.
• Cytotoxicity evaluation using BCA assay.

Main Results:

• Sodium substitution created structural vacancies in HA, leading to less stable Na-HA.
• Na-HA exhibited increased dissolution and enhanced formation of low-crystalline hydroxyl-carbonate apatite in SBF.
• Na-HA demonstrated significantly higher osteoconductivity in rabbit calvarial defects after 4 weeks.
• No statistically significant differences in cytotoxicity were observed between Na-HA and HA.

Conclusions:

• Sodium substitution induces structural defects in hydroxyapatite, enhancing its bioactivity.
• Na-HA shows improved apatite formation and superior osteoconductivity compared to HA.
• Na-HA is a promising candidate for bone grafting materials with enhanced bone regeneration potential.