Characterization of hydroxyapatite-tantalum pentoxide nanocomposite coating applied by electrophoretic deposition on Nitinol superelastic alloy

Abstract

In this study, natural hydroxyapatite (nHA) and nHA-20 wt.%Ta2O5 nanocomposite coatings were deposited via electrophoretic deposition (EPD) on the NiTi substrate. The suspensions of nHA and nHA-Ta2O5 nanoparticles were prepared in n-butanol as a medium with different contents (0, 4, 8, 12, 16, and 20 mL/L) of triethanolamine (TEA) as a dispersant. The most stable suspensions of nHA and nHA-Ta2O5 nanoparticles were achieved with 16 mL/L TEA according to the sedimentation test and zeta potential measurement results. The enhanced colloidal stability of nanoparticles in n-butanol by TEA addition was investigated by FTIR analysis. The highest in-situ EPD kinetics were accomplished from suspensions containing an optimum concentration of dispersant. The phase compositions and microstructures of the coatings, before and after sintering under 1.4 × 10−6 mbar vacuum at 800 °C for 1 h, were perused using XRD and FESEM, respectively. The results of the nano-scratch analysis showed the highest critical distance of delamination (0.38 mm), normal load before failure (133 mN) as well as the critical contact pressure (7.12 GPa) for nHA-Ta2O5 coating on the NiTi. The concentration of the released Ni ions from passivated-NiTi with nHA coating in PBS after 30 days of immersion reduced from 45.72 to 5.62 μg/Lcm2 by introducing Ta2O5 in nHA matrix. On the other hand, the improved corrosion behavior of passivated-NiTi with nHA-Ta2O5 coating in comparison to that of with nHA deposit was explained with the lower amount of open porosities in the microstructure. The biocompatibility of the nHA and nHA-Ta2O5 surfaces were studied by osteoblast cell attachment during 7 days of culturing.