Corrosion resistance of a Nitinol ocular microstent: Implications on biocompatibility

Abstract

Nitinol is commonly used in medical implants due to its unique thermomechanical properties of shape memory and superelasticity. Free nickel has the potential to induce biological responses that may be a concern for permanent implants manufactured from nickel‐containing alloys. Although there are extensive reports on the effects of surface treatments on corrosion behavior in cardiovascular Nitinol implants, there is a lack of data on corrosion resistance and impact on biocompatibility for ocular implants. Therefore, the objective of this study was to determine localized corrosion and nickel elution resistance of an electropolished Nitinol‐based ocular device (Hydrus Microstent, Ivantis, Inc.) intended for patients with primary open angle glaucoma. Pitting corrosion susceptibility was characterized by potentiodynamic polarization testing per ASTM F2129. In addition, nickel ion release was quantified with immersion testing to 63 days. The results indicated high localized corrosion resistance as all samples reached polarization potentials of 800 mV without pitting initiation. Maximum nickel elution rates per device were less than approximately 1.1 ng/device/day after the first day of immersion and reduced to less than 0.1 ng/device/day after 7 days. For a patient with bilateral microstents, these nickel concentrations are ×10,000 lower than previously published tolerable intake levels for systemic toxicity. Overall, these corrosion results are in good agreement with literature values of well processed and biocompatible Nitinol devices indicating adverse systemic biological responses are not expected in vivo.

Surface finishing of Nitinol for implantable medical devices: A review

“…20,24,25 There has been a lot of research done to improve the properties of surface oxide with a primary focus on how to prevent the release of nickel ions from NiTi. [26][27][28] Ni ions can be toxic, allergenic, and carcinogenic depending on the amount released and length of exposure. [29][30][31] The US Food and Drug Administration's (FDA) Center for Devices and Radiological Health (CDRH) recommends a tolerable intake of Ni for parenteral (nonoral) exposure as 0.5 μg/kg/day (e.g., 35 μg/day for a 70 kg adult).…”

“…There has been a lot of research done to improve the properties of surface oxide with a primary focus on how to prevent the release of nickel ions from NiTi 26–28 . Ni ions can be toxic, allergenic, and carcinogenic depending on the amount released and length of exposure 29–31 .…”

Modified Surface Composition and Biocompatibility of Core-Shell Nitinol Nanoparticles Fabricated via Laser Ablation of Differently Passivized Targets

“…Ten sets of nitinol targets were prepared out of which five sets were mechanically polished using 3,000 grade abrasive paper (Group A) while the remaining were used without polishing (Group B). Four different passivation procedures were carried out on each group sample, namely, heating in a muffle furnace [600 °C for 30 min (Oncel and Acma, 2017;Nagaraja and Pelton, 2020)], HNO 3 treatment [20% HNO 3 acid for 12 h at room temperature (Mirjalili et al, 2013;Norouzi and Nouri, 2021)], H 2 O 2 treatment (30% H 2 O 2 for 2 h under boiling conditions (Chu et al, 2006;Shabalovskaya et al, 2012;Nagaraja and Pelton, 2020)), and anodization [60 V DC, 15 min in the presence of 0.5% of NH 4 F eluted in a mixture of ethylene glycol with 2% DI water (Davoodian et al, 2020;Rahimipour et al, 2020)]. Table 1 describes S1 of the supplementary section.…”

Local release of metal ions from endovascular metallic implants in the human biological specimens: An overview of in vivo clinical implications

“…Corrosion by-products have been though to increase the risk of in-stent restenosis. Recent research [17,18] investigating whether nickel ions were elevated systemically or in local tissue due to corrosion in Nitinol stents. While no increase in nickel ion levels in blood or urine were observed in swine 6 months after implantation, there was evidence of increased nickel levels in local arterial tissue for corroded stents.…”