Effect of coating thickness on the shear strength and failure mode of plasma sprayed hydroxyapatite coatings to bone

The majority of this study was to evaluate the effect of coating thickness on the shear strength of hydroxyapatite coating (HAC) to bone. Plasma-sprayed HA-coated (50 μm and 200 μm) and grit-blasted Ti-6Al-V cylinders were transcortically implanted in femora of canines. After 4, 6, 8 and 12 weeks, the implant-bone interfacial shear strength was measured by the push-out test. The results showed that the mean shear strength of 50 μm-HAC implants was higher than that of 200 μm-HAC implants at each of time period, with significant difference (p<0.05) found at 4 and 12 weeks. Both the HAC implants revealed significant greater mean shear strength than the uncoated ones. The maximum shear strength was 14.91±4.28 MPa for 50 μm-HAC implant at 8 weeks. With bone attached to the surface of HACs under observations of scanning electron microscope (SEM). the failure mode for 50 μm-HACs was in all cases at the HAC-bone interface. However, for 200 μm-HACs, the failure modes occurred at the HAC-bone, inside the coating layer and at the HAC-Ti alloy interface were found.