Pulsed electrodeposition and characterization of HAp-Ta2O5 composite coating on NiTi for orthopedic applications

NiTi shape memory alloy has garnered profound attention in different biomedical applications; However, the possible toxicity caused by release of the Ni ions and the bioinert surface of this alloy have limited its use as permanent implant. In this study, hydroxyapatite- tantalum pentoxide (HAp-Ta 2 O 5 ) composite coatings were electrodeposited on the NiTi from the aqueous bath containing calcium nitrate tetrahydrate and ammonium dihydrogen phosphate salts along with different concentrations of Ta 2 O 5 nanoparticles, i.e., 0-1 g/L, under pulsed current at a density of 15 mA/cm 2 . The results demonstrated that the HAp phase is formed as a matrix and Ta 2 O 5 phase is successfully co-deposited with the matrix in the composite coatings. Surface morphology studies conducted by field-emission electron microscopy (FESEM) and obtained outcomes revealed that as the concentration of Ta 2 O 5 nanoparticles in the bath increased, the surface of the coatings became more compact. The potentiodynamic polarization (PDP) electrochemical test was conducted to evaluate the corrosion behavior of the deposited coatings. The results showed that the addition of the Ta 2 O 5 nanoparticles to the HAp matrix improved the corrosion resistance and decreased the Ni ion release of the samples up to 205% and 91%, respectively. The apatite formation was stimulated by the deposited coatings upon immersion in the simulated body fluid. These results suggest that HAp-Ta 2 O 5 composite coating electrodeposited from the bath containing 1 g/L of Ta 2 O 5 nanoparticles induces effective corrosion protection, decreases concentration of released Ni ions, and induces bioactivity, making the NiTi a more suitable material for permanent implantation by addressing the challenges.