Hydroxyapatite coatings on Ti produced by hot isostatic pressing

Area of Science:

• Biomaterials Engineering
• Surface Science
• Orthopedic Implants

Background:

• Plasma spraying is a common method for hydroxyapatite (HA) coatings on titanium (Ti) implants.
• These coatings exhibit porosity, dissolution, and weak substrate bonding, raising concerns about long-term interface strength.

Purpose of the Study:

• To develop an alternative method for producing HA coatings on Ti substrates.
• To overcome the limitations of plasma-sprayed coatings, specifically improving density and bond strength.

Main Methods:

• Hydroxyapatite (HA) powder was mixed with water and air-sprayed onto Ti substrates.
• Specimens underwent cold pressing, encapsulation in platinum foil and glass, followed by Hot Isostatic Pressing (HIP) at 850°C and 1000 bar.
• Post-HIP processing involved removing the glass and platinum foil.

Main Results:

• The HIP-processed HA coatings were significantly denser than plasma-sprayed coatings.
• Measured bonding strength exceeded 62 MPa, considered satisfactory.
• X-ray diffraction and IR spectroscopy confirmed the coating structure matched HA.
• Vertical cracks were observed in the coatings.

Conclusions:

• Hot isostatic pressing (HIP) is a viable technique for producing dense, well-bonded HA coatings on titanium.
• The observed bonding strength suggests improved long-term implant stability.
• Further in vivo studies are required to assess the clinical acceptability of the observed coating microstructures, particularly the cracks.