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

Abstract

Metallic medical devices such as intravascular stents can undergo fretting damage in vivo that might increase their susceptibility to pitting corrosion. As a result, the US Food and Drug Administration has recommended that such devices be evaluated for corrosion resistance after the devices have been fatigue tested in situations where significant micromotion can lead to fretting damage. Three common alloys that cardiovascular implants are made from [MP35N cobalt chromium (MP35N), electropolished nitinol (EP NiTi), and 316LVM stainless steel (316LVM)] were selected for this study. In order to evaluate the effect of wire fretting on the pitting corrosion susceptibility of these medical alloys, small and large fretting scar conditions of each alloy fretting against itself, and the other alloys in phosphate buffered saline (PBS) at 37°C were tested per ASTM F2129 and compared against as received or PBS immersed control specimens. Although the general trend observed was that fretting damage significantly lowered the rest potential (Er) of these specimens (p < 0.01), fretting damage had no significant effect on the breakdown potential (Eb, p > 0.05) and hence did not affect the susceptibility to pitting corrosion. In summary, our results demonstrate that fretting damage in PBS alone is not sufficient to cause increased susceptibility to pitting corrosion in the three common alloys investigated.

The use of electrochemical techniques to evaluate the corrosion performance of metallic biomedical materials and devices

“…Studies of the effect of fretting on the breakdown behavior have produced conflicting results. In one study, it was found that fretting produced by rotating a wire against another wire did not have a significant effect on E b for MP35N, EP nitinol, or 316LVM stainless steel . In another study, however, fretting produced in axial fatigue tests of overlapped EP nitinol and stainless steel (grade not given) stents resulted in breakdown, whereas non‐fatigued stents did not exhibit breakdown up to about 0.9 V .…”

“…In most cases, pitting on the fatigued stents occurred in the fretting damaged areas. The question of whether axial loading itself played a role has been raised, but other work has shown that nitinol wire subject to 4% tensile strain, resulting in the formation of stress‐induced martensite, does not exhibit a substantial change in localized corrosion resistance . Similarly, EP nitinol deformed by bending to 10% strain was found to remain resistant to breakdown up to about 1 V…”

Endovascular Devices and Revascularization Techniques for Limb-Threatening Ischemia in Individuals With Diabetes

“…It fails to exhibit the shape memory traits found with nitinol, and is relatively bulky, and is hence less frequently utilized. 59 Each material corrodes differently, which also influences the durability. 59 There are several characteristics used to categorize stents.…”

“…59 Each material corrodes differently, which also influences the durability. 59 There are several characteristics used to categorize stents. Stents can be either self-expanding or balloon-expandable.…”

Synthesis and in-vitro antibacterial properties of a functionally graded Ag impregnated composite surface

“…The bio-functional surface layer provides antibacterial activity because of the antibacterial agents and the bottom S-phase layer shows excellent wear and corrosion resistance, which also provide good load bearing capacity due to its high hardness. Metallic medical devices as cardiovascular implants made by SS can undergo in vivo fretting damage which can enhance their susceptibility to pitting corrosion damage [25]. Pitting is typically initiated from the surface defects, which can be decreased due to the dense S-phase layer [26].…”