The effect of fatigue on the corrosion resistance of common medical alloys

Abstract

The effect of mechanical fatigue on the corrosion resistance of medical devices has been a concern for devices that experience significant fatigue during their lifespan and devices made from metallic alloys. The Food and Drug Administration had recommended in some instances for corrosion testing to be performed on post-fatigued devices [Non-clinical tests and recommended labeling for intravascular stents and associated delivery systems: guidance for industry and FDA staff. 2005: Food and Drug Administration, Center for Devices and Radiological Health], although the need for this has been debated [Nagaraja S, et al., J Biomed Mater Res Part B: Appl Biomater 2016, 8.] This study seeks to evaluate the effect of fatigue on the corrosion resistance of 5 different materials commonly used in medical devices: 316 LVM stainless steel, MP35N cobalt chromium, electropolished nitinol, mechanically polished nitinol, and black oxide nitinol. Prior to corrosion testing per ASTM F2129, wires of each alloy were split into subgroups and subjected to either nothing (that is, as received); high strain fatigue for less than 8 min; short-term phosphate buffered saline (PBS) soak for less than 8 min; low strain fatigue for 8 days; or long-term PBS soak for 8 days. Results from corrosion testing showed that the rest potential trended to an equilibrium potential with increasing time in PBS and that there was no statistical (p >0.05) difference in breakdown potential between the fatigued and matching PBS soak groups for 9 out of 10 test conditions. Our results suggest that under these nonfretting conditions, corrosion susceptibility as measured by breakdown potential per ASTM F2129 was unaffected by the fatigue condition.

Effect of wire fretting on the corrosion resistance of common medical alloys

“…After undergoing fretting testing, p ‐values were obtained to statistically compare rest, breakdown, and over potential values between pairs of as received, soak, small, and large fretted samples composed of the same alloy as shown in Table . As observed in a previous study, comparisons between MP35N as received and soak samples yielded significantly different results for the rest potential ( p = 0.002). Half of the comparisons between the as received/soak and fretted MP35N samples resulted in significantly different rest potential values with all the soak vs large fretted MP35N comparisons showing statistical significance ( p < 0.001).…”

“…Cardiovascular devices constructed of metallic alloys can undergo fretting and fatiguing conditions in vivo , both of which could damage the protective oxide layer on their surfaces and potentially lead to pitting corrosion. In a previous study performed in our laboratory, fatigue conditions alone were shown to not significantly affect the pitting corrosion susceptibility of metallic alloys commonly implanted in vivo . The work herein set out to determine the effect that wire fretting alone has on the pitting corrosion susceptibility of several metallic alloys commonly used to manufacture intravascular stents.…”

“…In some cases, such as MP35N small fretted against 316LVM, the rest potential was higher for the fretted samples as compared to the as received control although not to the point of statistical significance. As was shown in a previous study, a key factor that resulted in significantly higher rest potentials was immersion time in PBS . That is, although these MP35N samples underwent small fretting damage against 316LVM, their immersion time was about twice as long in PBS (about 70 minutes longer during fretting testing) as compared to the as received MP35N samples.…”

“…In a previous study examining the effect of fatigue on the susceptibility of pitting corrosion, wire samples of 316LVM stainless steel, MP35N cobalt chromium, and nitinol that underwent fatigue testing prior to testing for pitting corrosion susceptibility per ASTM F2129 were compared with control samples that did not undergo fatigue testing. Although evidence of crack formations were present along the surface of wire samples, corrosion testing revealed that fatigue did not alter the pitting corrosion susceptibility . Furthermore, it was shown that immersion time in phosphate buffered saline (PBS) was a driving factor behind significant differences in rest potential (E r ), which was consistent with other findings .…”

Sodium Hypochlorite Treatment and Nitinol Performance for Medical Devices

“…Corrosion susceptibility as measured by ASTM F2129 was generally unaffected by the NaClO soak in our tests. Regardless of NaClO condition, EP nitinol had higher breakdown potentials than BO nitinol similar to other studies (Ref 16, 22). The NaClO soak led to a statistically significant decrease in rest potential for the BO nitinol although the absolute change in average E r was within the range of expected variability for the test as described in ASTM F2129.…”