The ultrastructure of the plasma-sprayed hydroxyapatite-bone interface predisposing to bone bonding

Area of Science:

• Biomaterials Science
• Orthopedic Research
• Tissue Engineering

Background:

• Bone formation on hydroxyapatite implants involves surface dissolution and biological apatite reprecipitation.
• In vitro studies indicate that increased coating crystallinity hinders dissolution and reprecipitation.
• Understanding the effect of crystallinity on bone bonding is crucial for implant design.

Purpose of the Study:

• To investigate the impact of hydroxyapatite coating crystallinity on the mechanism of bone bonding in vivo.
• To compare the mineralization process on hydroxyapatite coatings with normal ossification.

Main Methods:

• Plasma-sprayed hydroxyapatite (PSHA) coated titanium alloy implants were used, with some coatings annealed to increase crystallinity.
• Implants were surgically placed in canine femora and tibiae for 3 hours, 3 days, and 10 days.
• Transmission electron microscopy with an anhydrous embedding technique was employed to analyze bone-implant interfaces.

Main Results:

• Biological apatite crystallites precipitated on non-annealed PSHA coatings within 3 hours of implantation.
• Differences in the ultrastructure of the mineral phase were observed between non-annealed and annealed surfaces at 3 and 10 days.
• The mechanism of bone mineralization associated with hydroxyapatite coatings closely resembled normal ossification.

Conclusions:

• Coating crystallinity influences early biological apatite deposition on hydroxyapatite implants.
• Despite initial differences, hydroxyapatite coatings facilitate bone mineralization through mechanisms similar to natural bone formation.
• These findings support the use of hydroxyapatite coatings for enhanced bone integration in orthopedic implants.