Electrophoretic deposition of SiO2 coatings on nitinol: The effect of suspension pH on tailoring film properties

Nickel–titanium alloys are widely used in cardiovascular implants because of their shape-memory behavior and superelasticity, yet they can release nickel ions that trigger inflammation and hinder endothelialization. In this study, amorphous SiO2 nanopowders were deposited onto NiTi substrates using electrophoretic deposition (EPD), and the effect of suspension pH on coating structure, physicochemical properties, and biological response was investigated. Zeta potential measurements showed consistently positive values at all pH levels, confirming effective charge masking by polyethylenimine (PEI). Despite similar electrokinetic behavior, scanning electron microscopy revealed clear pH-dependent differences in morphology. At pH 4, coatings were dense, compact, and exhibited nearly complete surface coverage with local microcracks, whereas coatings produced at pH 8 were more heterogeneous and showed directional agglomeration. FT-IR and SEM–EDS analyses confirmed the coexistence of SiO2 and PEI, along with greater elemental uniformity at pH 4. These coatings were also thicker, more cohesive, and offered superior wear resistance and barrier performance compared to those formed at pH 8. Biological tests demonstrated that SiO2-modified surfaces reduced cell adhesion and viability relative to bare NiTi. The results indicate the need to balance protective functionality with biocompatibility, providing guidance for further optimization of SiO2-based coatings for NiTi cardiovascular implants.