Abstract
In the current research, the composite coatings of hydroxyapatite‑tantalum pentoxide-multi walled carbon nanotubes (HA-Ta2O5-MWCNTs) were deposited on NiTi substrate by applying electrophoretic deposition (EPD) method at 60 V for 80 s. The suspensions were prepared by incorporating 0.5, 1, 1.5, and 2 wt% of MWCNTs with 20 g/L HA and 20 wt% Ta2O5. After sintering the samples at 700 °C for 1 h, the phase compositions and structures of coatings were studied using XRD and SEM devices, respectively. According to the XRD patterns, no additional phases were recognized in compositions of coatings, excluding the primary phases that the coating was manufactured from them. It was observed from SEM images that the MWCNTs induced the network structures and acted as bridges between nanoparticles in HA-Ta2O5 coating. As a result of the micro-indentation test, the HA-Ta2O5-2MWCNTs coating provided the highest elastic modulus (47.36 GPa) for NiTi substrate (56.36 GPa). It also caused the hardness enhancement of HA coating from 0.13 GPa to 3.17 GPa. The fracture toughness of HA-Ta2O5 coating, measured from nano-scratch data, was augmented from 0.95 MPam1/2 to 1.7 and 2.3 MPam1/2 by adding 1 and 2 wt% MWCNTs, respectively. This enhancement was attributed to the electrostatic adsorption of nanoparticles on MWCNTs and formation of MWCNTs bridges in structures. The bioactivity was studied by immersion of samples in the simulated body fluid (SBF) for 7 days at 37 °C. The biocompatibility of samples was assessed by considering cytotoxicity behavior and morphological studies after the cell culture. During 3 days of culture, the optical densities of cells on HA-Ta2O5 were enhanced up to 22.9 %, 50 %, 60.4 %, and 70.8 % by the addition of 0.5, 1, 1.5, and 2 wt% MWCNTs, respectively. The affirmative influence of MWCNTs addition on bioactivity and biocompatibility of HA-Ta2O5 coating was ascribed to the increment in negative charge density of the surface.
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