Multiwalled-carbon nanotubes reinforced hydroxyapatite- tantalum pentoxide nanocomposite coating on Nitinol alloy: Antibacterial activity and Electrochemical properties

In this work to establish the antibacterial implants, the different amounts of multi-walled carbon nanotubes (MWCNTs, 0.5, 1, 1.5, and 2 wt.%) were incorporated with hydroxyapatite-tantalum pentoxide (HA-Ta2O5) and exerted on the NiTi by electrophoretic deposition (EPD) method. The increased HA-Ta2O5 coating density by adding and enhancing the MWCNTs content was shown by field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM). It was affirmed that MWCNTs have still been stable in HA-Ta2O5−MWCNTs coatings after sintering at 700 °C for 1 h. The increase of MWCNTs from 0.5 to 2 wt.% caused an increment of adhesion strength of HA-Ta2O5 coating to NiTi from 10 to 27% due to providing the more contact surface area of the coating with substrate and consequently the higher chemical bonding. It was found that the antibacterial property of the HA-Ta2O5 coating was induced by MWCNTs. Such behavior originated from the antibacterial characteristic of MWCNTs and has successively improved due to the rise in MWCNTs content and concurrent diminish in HA-Ta2O5−MWCNTs surface wettability. The positive effect of MWCNTs on the electrochemical behavior of HA-Ta2O5-coated NiTi was confirmed by polarization test and electrochemical impedance spectroscopy (EIS). According to the parameters resulted from the fitting of EIS spectra with the electrical circuits (EC), the resistances of the coating and the double-layer on NiTi surface have increased due to an enhancement in the MWCNTs content. This improvement was attributed to the increased density and reduced wettability of HA-Ta2O5 coating.