Characterization of hydroxyapatite: before and after plasma spraying

Area of Science:

• Materials Science
• Biomaterials Engineering
• Surface Chemistry

Background:

• Hydroxyapatite (HA) is a key biomaterial for bone regeneration.
• Plasma spraying is a common method for coating HA onto implants.
• Understanding structural changes post-plasma spraying is crucial for material performance.

Purpose of the Study:

• To characterize structural modifications of hydroxyapatite powder after plasma spraying.
• To investigate the influence of plasma spraying on HA's thermal stability and hydroxyl group configurations.
• To assess the rehydroxylation tendency of dehydroxylated HA.

Main Methods:

• Infrared (IR) spectroscopy was used to analyze structural changes.
• Thermoanalytical techniques (e.g., TGA/DSC) were employed for thermal characterization.
• HA powder was analyzed before and after plasma spraying.

Main Results:

• Plasma spraying induced structural changes in HA, including dehydroxylation and the formation of misoriented hydroxyl ions.
• IR spectra showed decreased O-H stretching and librational modes, with a new band near 3400 cm(-1) for misoriented hydroxyls.
• Thermoanalysis revealed adsorbed water release below 500°C and HA dehydroxylation starting around 700°C, with a tendency for dehydroxylated HA to rehydroxylate above 500°C in inert atmospheres.

Conclusions:

• Plasma spraying significantly perturbs the structure of hydroxyapatite powder.
• The observed dehydroxylation and rehydroxylation behavior suggest altered thermal stability and potential for structural recovery.
• These findings are important for optimizing plasma-sprayed HA coatings for biomedical applications.