Further studies on the plasma-sprayed amorphous phase in hydroxyapatite coatings and its deamorphization

Area of Science:

• Biomaterials Science
• Materials Chemistry
• Surface Engineering

Background:

• Plasma-sprayed hydroxyapatite (HA) coatings are widely used in biomedical implants.
• These coatings often contain a significant amorphous phase, impacting their properties.
• Understanding the nature and behavior of this amorphous phase is crucial for optimizing HA coatings.

Purpose of the Study:

• To characterize the amorphous phase in plasma-sprayed HA coatings.
• To investigate the effect of heat treatment on the amorphous phase transformation.
• To evaluate the solubility and stability of amorphous oxyapatite.

Main Methods:

• Infrared (IR) spectroscopy for phase identification.
• Solubility tests in lactic acid.
• Analysis of the influence of water on phase transformation during plasma spraying.

Main Results:

• Plasma-sprayed coatings contain amorphous oxyapatite, not pure hydroxyapatite.
• Amorphous oxyapatite exhibits higher solubility in lactic acid compared to crystalline HA.
• Heat treatment effectively converts amorphous oxyapatite to crystalline hydroxyapatite, reducing dissolution rates.
• Water molecules can accelerate the amorphous to crystalline transformation during plasma spraying.

Conclusions:

• Plasma-sprayed HA coatings are predominantly oxyhydroxyapatite with a substantial amorphous oxyapatite component.
• The amorphous phase's higher solubility necessitates control over its content for stable implant coatings.
• Heat treatment is a viable method to enhance the stability and reduce the dissolution of these coatings.