In vitro dissolution behaviour of two morphologically different thermally sprayed hydroxyapatite coatings

Area of Science:

• Biomaterials Science
• Materials Engineering
• Surface Science

Background:

• Hydroxyapatite coatings enhance osseointegration of titanium implants.
• Different spraying techniques influence coating properties and performance.
• Understanding coating stability in physiological conditions is crucial for clinical success.

Purpose of the Study:

• To compare the stability of hydroxyapatite coatings produced by vacuum plasma spraying (VPS) and detonation gun spraying (DGUN) in Ringer's solution.
• To investigate the effects of spraying method on coating crystallinity, porosity, residual stress, and surface morphology.
• To correlate coating characteristics with dissolution behavior over time.

Main Methods:

• Hydroxyapatite coatings were applied to titanium substrates using VPS and DGUN techniques.
• Coatings were immersed in Ringer's solution (pH 7.2, 37°C) for up to eight weeks.
• Characterization included X-ray diffraction (XRD) for crystallinity and stress, optical microscopy for porosity and thickness, and scanning electron microscopy (SEM) and Talysurf for surface morphology.

Main Results:

• DGUN coatings exhibited lower initial crystallinity and porosity but higher surface roughness and residual stress compared to VPS coatings.
• VPS coatings demonstrated higher stability and a lower dissolution rate throughout the immersion period.
• The initial properties influenced the long-term degradation behavior of the hydroxyapatite coatings.

Conclusions:

• Vacuum plasma spraying (VPS) produces more stable hydroxyapatite coatings on titanium substrates than detonation gun spraying (DGUN) under physiological conditions.
• Coating stability is significantly influenced by initial crystallinity, porosity, and residual stress levels.
• VPS coatings are preferable for applications requiring enhanced durability and reduced dissolution in biological environments.