Coatings based on calcium phosphate with thicknesses of 0.5 and 2 μm were obtained by high-frequency magnetron sputtering on NiTi substrates in an argon atmosphere. The coating was characterized using X-ray diffraction, scanning electron microscopy, atomic force microscopy, and in vitro cytocompatibility and bioactivity studies. A biphasic coating of tricalcium phosphate (Ca₃(PO₄)₂) and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) with a 100% degree of crystallinity was formed on the surface. The layer enriched in calcium, phosphorus, and oxygen was observed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Scanning electron microscopy showed that the surface structure is homogeneous without visible defects. The 2 µm thick coating obtained by sputtering with a deposition time of 4 h and a deposition rate of 0.43 µm/h is uniform, contains the highest amount of the calcium phosphate phase, and is most suitable for the faster growth of cells and accelerated formation of apatite layers. Samples with calcium phosphate coatings do not cause hemolysis and have a low cytotoxicity index. The results of immersion in a solution simulating body fluid show that NiTi with the biphasic coating promotes apatite growth, which is beneficial for biological activity.

The present work is aimed at studying the surface cytocompatibility of porous NiTi obtained by self-propagating high temperature synthesis (SHS), and then annealed in air at 500–1000 °C. Using cytotoxicity tests in vitro, it was found that the cells had attached to the oxidized surface in the amount sufficient for their growth and proliferation on the substrate. The surfaces of the annealed samples and the control sample were studied by XRD, SEM and optical microscopy. It was found that there is a correlation between cell hemolysis and nickel-containing phases on the surface. Thus, annealing at 500–700 °C worsens cytocompatibility compared to the control sample, but annealing at 800–1000 °C improves cytocompatibility.

Hydroxyapatite coatings were deposited for 1, 2, and 3 h on NiTi substrates using plasma-assisted radio frequency sputtering. The matrix consisted of NiTi B2 and NiTi B19’ phases and Ti₂Ni, Ni₃Ti, and Ni₄Ti₃ intermetallic compounds. The surface coating was monoclinic hydroxyapatite. Increasing the deposition time to 3 h made it possible to form a dense hydroxyapatite layer without visible defects. The phase contrast maps showed that the coating consisted of round grains of different fractions, with the smallest grains in the sample deposited for 3 h. The wettability tests showed that the coating deposited for 3 h had the highest surface energy, reflected in the proliferation density of the MCF-7 cell line.