Corrosion of NiTi stents induced by galvanic interaction with radiopaque materials

Nickel titanium (NiTi) alloys are used as a base material for biomedical devices and implants, such as stents. One limitation associated with NiTi stents is the low radiopacity. Thus, radiopaque markers, made of noble materials, are usually attached to NiTi stents to increase the stent radiopacity, raising concerns regarding galvanic corrosion in body fluid environments. This research aims to assess the galvanic interactions of NiTi alloys and NiTi stent when coupled to radiopaque markers materials in simulated body fluid solution (NaCl 0.9%). Electrochemical measurements, using flat specimens and NiTi stents were carried out. After the tests, scanning electron microscopy (SEM) surface analysis was performed. The results from polarization curves indicate that the NiTi/Platinum (NiTi/Pt) couple is more susceptible to galvanic corrosion than the pairs of NiTi/Palladium (NiTi/Pd) and NiTi/Gold (NiTi/Au). The potential difference of 628 mV presented by the NiTi/Pt couple was the highest among the galvanic couples investigated. Higher values of galvanic potential and galvanic current were also obtained by the pair NiTi/Pt. In direct galvanic short-term measurements with NiTi stent/Pt, no increase in the current density or presence of pits on the NiTi stent surface was observed. However, long-term potentiostatic test, applying 280 mV, which corresponds to the galvanic potential of the NiTi/Pt couple, resulted in current peaks of 1.500 µA and led to severe localized corrosion of NiTi stents, revealing a risk of corrosion induced by coupling Pt markers to NiTi stent.