The study of morphological evolution, biocorrosion resistance, and bioactivity of pulse electrochemically deposited Hydroxyapatite/ZnO composite on NiTi superelastic alloy

Abstract

In this work, the effect of zinc oxide nanoparticles on hydroxyapatite deposited on NiTi superelastic alloy was studied. Various concentrations of nanoparticles (200, 400, and 800 mg/L) along with cetrimonium bromide (100 mg/L) as a dispersant agent were added to the coating electrolyte. Morphological observations showed that zinc oxide encouraged hydroxyapatite plate-like crystals to grow in longitudinal and transverse directions, turning into a bone-like structure with greater pores. XRD and FTIR indicated the favorable impact of zinc oxide on the synthesis of pure hydroxyapatite as the most stable calcium phosphate phase. Next, the corrosion evaluations revealed that zinc oxide successfully reduced the corrosion current density of composite coatings down to 1.35 nA/cm2, where pure calcium phosphate coating exhibited 19.05 nA/cm2. Topographic evaluations (AFM) proved a consistent rise in roughness parameters where the roughness average climbed from 208.3 nm for calcium phosphate coating up to 436.45 nm for the composite coating with the highest ZnO concentration. The adhesion strength of composite coatings was above 15 MPa (the critical requirement for orthopedic applications), despite calcium phosphate coating. The wettability results also differed dramatically where calcium phosphate coating exhibited 31.17°, but it dropped to 12.62° for the composite coating formed in the solution containing 400 mg/L ZnO nanoparticles. Ultimately, bioactivity analysis in simulated body fluid revealed that ZnO nanoparticles not only promoted growth but also restricted the size distribution of cauliflower-like apatite grains.