Mechanical and histological evaluation of a plasma sprayed hydroxyapatite coating on a titanium bond coat

To improve the biological stability of hydroxyapatite-coated implants, the use of an appropriate commercial pure titanium bond coat (CP-Ti) is an effective method for significant improvement in the interface bonding and stress reduction of the plasma-sprayed HA coating and Ti-alloy system. The purpose of this study was to determine the effect of plasma-sprayed CP-Ti on the in vivo properties of the HA coating on Ti6Al4V. According to the experimental results, samples with an HA coating on the CP-Ti (Ti-HA coating) display a lower and ineffective residual stress than samples without the bond coat. The CP-Ti provides a very rough surface and results in a higher adhesive strength between the HA and CP-Ti. In the in vivo test, after the intramedullary implantation, the histological observation showed the apposition of the new bone tissue directly onto the HA coating. The shear strength between the bone and the Ti-HA coating was higher than that without CP-Ti after 12 weeks of implantation (5.15 vs. 1.41 MPa). The failure mode analysis showed the failure mainly occurring at the surrounding bone, with some failure at the HA/CP-Ti interface. The excellent bio-durability and mechanical properties of the HA coating in this study contributed to the reduction of the compressive residual stress in the HA coating and to the enhancement of interface adhesive strength by introducing the commercial pure titanium bond coat.