Dissolution kinetics of calcium phosphate coatings

Area of Science:

• Materials Science
• Biomaterials Engineering
• Surface Chemistry

Background:

• Plasma spray and HVOF techniques create coatings with amorphous and crystalline phases.
• Amorphous phases in coatings are linked to higher calcium ion release.
• Coating stability is influenced by phase composition and processing methods.

Purpose of the Study:

• To investigate the relationship between coating phase composition (amorphous vs. crystalline) and ion release.
• To compare the dissolution rates of amorphous and crystalline coatings under varying conditions.
• To assess the impact of heat treatment on coating stability and ion release.

Main Methods:

• Coating fabrication using plasma spray, HVOF, ion beam sputtering, and RF magnetron sputtering.
• X-ray powder diffraction (XRD) for phase analysis.
• Dissolution testing in Hank's calcium-free balanced salt solutions and buffered solutions (pH 6.50).
• Measurement of calcium ion release and coating dissolution rates.

Main Results:

• Coatings with higher amorphous content exhibited greater calcium ion release.
• Amorphous coatings produced by sputtering dissolved rapidly, while heat-treated (crystalline) coatings were more stable.
• Dissolution rates were significantly higher for amorphous coatings at pH 6.50 compared to heat-treated coatings.
• Reprecipitation of calcium phosphate occurred on amorphous coatings in physiological pH solutions, slowing dissolution.

Conclusions:

• The amorphous phase is the primary source of calcium ion release from coatings.
• Heat treatment significantly improves coating stability by promoting crystalline phases.
• Coating stability and dissolution behavior are highly dependent on phase composition and environmental pH.