The effect of dissolution on plasma sprayed hydroxylapatite coatings on titanium

Area of Science:

• Biomaterials Science
• Materials Engineering
• Surface Chemistry

Background:

• Hydroxylapatite (HA) coatings are widely used on titanium implants to enhance osseointegration.
• Understanding the stability and degradation of HA coatings in physiological environments is crucial for long-term implant performance.

Purpose of the Study:

• To investigate the structural and compositional changes of plasma-sprayed HA coatings on titanium after immersion in a calcium-free Hank's balanced salt solution.
• To evaluate the effect of dissolution on the interfacial shear bond strength of HA coatings over time.

Main Methods:

• Plasma-sprayed HA coated titanium specimens were immersed in Ca-free Hank's solution for 1, 2, 4, and 6 weeks.
• Coating analysis included X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy.
• Shear bond strength testing was performed at 2- and 6-week intervals.

Main Results:

• XRD confirmed the retention of the basic apatitic structure, with a slight loss of amorphous material.
• FTIR and Raman spectroscopy indicated no loss of phosphate groups but a decrease in hydroxyl content and an increase in carbonate content.
• Average shear bond strengths were 14.82 MPa (as-sprayed), 12.51 MPa (2 weeks), and 12.54 MPa (6 weeks), with no statistically significant reduction.

Conclusions:

• Plasma-sprayed HA coatings exhibit good structural integrity in a calcium-free simulated physiological environment for up to 6 weeks.
• Dissolution mechanisms lead to minor compositional changes, including hydroxyl loss and carbonate uptake.
• The interfacial shear bond strength of the HA coating remains largely unaffected after 6 weeks of immersion.