Structure and immersion behavior of plasma-sprayed apatite-matrix coatings

Area of Science:

• Biomaterials Science
• Materials Engineering
• Surface Chemistry

Background:

• Hydroxyapatite (HA) coatings are crucial for enhancing the biocompatibility and osseointegration of metallic implants, particularly on titanium alloys like Ti-6Al-4V.
• Understanding the influence of composite powder composition on coating properties and in vitro bioactivity is essential for developing advanced orthopedic and dental materials.

Purpose of the Study:

• To investigate the microstructure, properties, and simulated body fluid (SBF) immersion behavior of plasma-sprayed coatings derived from sinter-granulated HA composite powders containing SiO2, CaO, P2O5, and Na2O.
• To evaluate the effect of different elemental additions on the phase stability, bond strength, and apatite formation capability of HA coatings.

Main Methods:

• Fabrication of sinter-granulated HA composite powders incorporating SiO2, CaO, P2O5, and Na2O.
• Plasma spraying of these powders onto Ti-6Al-4V substrates to create coatings.
• Characterization of powder and coating microstructures using X-ray diffraction (XRD).
• Measurement of coating bond strengths.
• Immersion testing of coatings in simulated body fluid (SBF) and analysis of surface precipitation and ion concentration changes.

Main Results:

• Sinter-granulated HA composite powders were irregularly shaped. P2O5 and SiO2 promoted HA decomposition during powder fabrication, while CaO and Na2O did not.
• Plasma spraying induced further HA decomposition and phase reactions. All coatings achieved high bond strengths (45-50 MPa).
• During SBF immersion, alpha- and beta-tricalcium phosphate (TCP) phases decreased, and apatite precipitated on all surfaces. The SiO2- and CaO-containing HA (HSC) coating exhibited the highest apatite precipitation rate.

Conclusions:

• Plasma-sprayed HA coatings containing SiO2 and CaO demonstrate enhanced bioactivity, evidenced by a higher rate of apatite precipitation in SBF.
• The composition of HA composite powders significantly influences phase stability and bioactivity, with specific additives like SiO2 and CaO promoting favorable surface reactions.
• These findings suggest that tailored HA composite coatings can improve the biological response of titanium implants, potentially leading to better osseointegration.