Hydroxyapatite coating modifies implant membrane formation. Controlled micromotion studied in dogs

Area of Science:

• Biomaterials Science
• Orthopedic Surgery
• Tissue Engineering

Background:

• Controlled micromovements between bone and implants can affect osseointegration.
• Porous titanium (Ti) and hydroxyapatite (HA)-coated implants are used in orthopedic applications.
• Understanding implant stability and coating effects is crucial for successful bone ingrowth.

Purpose of the Study:

• To investigate the influence of controlled micromovements on bone ingrowth in Ti and HA-coated implants.
• To evaluate the effect of hydroxyapatite coating on implant fixation and stability under dynamic loading.
• To compare the histological and mechanical properties of stable versus unstable implants.

Main Methods:

• Developed a dynamic loading device to induce ~150-micron axial translation in knee implants.
• Inserted stable and unstable porous Ti or HA-coated implants (0.75 mm gap) into canine femoral condyles.
• Conducted histological analysis and shear strength testing after 4 weeks.

Main Results:

• Micromovements induced a fibrous membrane, inhibiting bone ingrowth, unlike stable implants.
• Unstable HA implants showed a thinner membrane with fibrocartilage and higher collagen than unstable Ti implants.
• HA coating enhanced shear strength, with stable HA implants exhibiting tenfold greater strength than stable Ti implants.

Conclusions:

• Micromovements between bone and implants disrupt osseointegration, leading to fibrous tissue formation.
• Hydroxyapatite coating enhances implant fixation, even under unstable conditions, due to improved membrane characteristics.
• Stable hydroxyapatite-coated implants provide the strongest mechanical anchorage and promote the most significant bone ingrowth.