Surface modification of titanium alloys and its effects on corrosion resistance and cell response

This study investigates the corrosion behavior and biocompatibility of titanium alloys (CP-Ti, TN15, and TNZ40) treated by Plasma Electrolytic Oxidation (PEO) for biomedical applications. Commercially pure titanium (CP-Ti) exhibited oxide phases composed of anatase (A) and rutile (R), while the metastable α′ Ti–15Nb (TN15) alloy and the body-centered cubic (BCC) multiprincipal β Ti–40Nb–40Zr (TNZ40) alloy were also evaluated. The morphological features of the PEO coatings on CP-Ti and TN15 were similar, presenting a predominantly rounded pore structure. In contrast, the TNZ40 surface exhibited a more irregular morphology. The coating thickness of the TN15 surface was higher than that of CP-Ti and TNZ40, while the latter two showed comparable values of approximately 10 μm. Surface roughness was similar for TN15 and TNZ40 (1.15 μm), both slightly higher than that observed for PEO-treated CP-Ti (0.9 μm). The average crystallite size of the anatase phase increases in the TN15 alloy ten times more compared to CP-Ti, followed by a significant reduction in the TNZ40 alloy. Electrochemical polarization and electrochemical impedance spectroscopy (EIS) results demonstrated that the PEO treatment significantly enhanced the corrosion resistance of all alloys, with particularly improved performance for TN15 and TNZ40. Overall, the corrosion resistance of the coated alloys was substantially higher than that of CP-Ti, indicating the formation of a more protective oxide layer. EIS analysis further confirmed improved passive film stability, with TNZ40 exhibiting the best electrochemical performance among the investigated materials. Biological performance was assessed using osteoblastic cells cultured on uncoated and coated surfaces. Cell viability (MTT assay) and adhesion tests indicated good cytocompatibility for all treated samples, with TNZ40 presenting the highest cell viability. Osteoblastic cells showed favorable interaction with the modified surfaces, and enhanced adhesion was observed on PEO-treated specimens. Morphological observations revealed that the porous and rough surface topography promoted cell attachment and migration, which are essential processes for bone tissue integration.