In Vitro Biological Characterization of Natural Hydroxyapatite/Single-Walled Carbon Nanotube Composite Coatings Synthesized by Electrophoretic Deposition on NiTi Shape Memory Alloy

Abstract

In the current work, the composite coating of natural hydroxyapatite (nHA)/single-walled carbon nanotubes (SWCNTs) with various contents of SWCNTs (0, 0.5, 1, and 2 wt.%) was applied on NiTi using electrophoretic deposition (EPD). Before the deposition process, the nanotubes were functionalized following the chemical oxidation method and characterized by FTIR. The sintering of samples was conducted at 800 °C for 3 h in a tube furnace under an argon atmosphere. The surface and cross-sectional microstructure of coatings was studied using a scanning electron microscope. The x-ray diffraction was utilized to investigate the effect of the SWCNTs secondary phase on the phase composition of the nHA layer after sintering. The incorporation of SWCNTs into the nHA layer resulted in the decomposition of some HA into the β-tricalcium phosphate phase. The tensile test was applied and displayed the enhancement in adhesion strength of nHA coating from 17.2 to 25 MPa after composing with 2 wt.% SWCNTs. The wettability of surfaces was assessed by measuring DMEM cell culture contact angles. The appraisement of the Ni ions release from the substrate demonstrated that the lowest release of Ni ions into DMEM cell culture after 7 days of incubation is achieved from NiTi coated with nHA-1 wt.% SWCNTs. The in vitro biocompatibility of the samples was pursued by MG63 osteoblast cell culturing and MTT assay. The highest cell attachment and proliferation on nHA-1 wt.% SWCNTs coating were attributed to the least toxic Ni ions release from the substrate of that.