Understanding the Effects of Force, Motion, Frequency, and Wire Diameter on Nitinol Wear

Braided wire nitinol devices are commonly used to treat a wide range of cardiovascular issues, ranging from vascular stents to occluder devices. While wire fatigue is still a concern as a cause for wire fracture, there is a growing body of evidence that wire fracture due to wear may be the dominant fracture mechanism. The wear performance of nitinol wire, however, is not well understood, both in laboratory bench testing conditions and in vivo. This study analyzed the effects of force, motion, frequency, and wire diameter on nitinol wear.

Nitinol wire with diameters ranging from 0.005” to 0.02” were used for the testing. All wires were electropolished and confirmed to have a nominally smooth surface prior to testing. For all tests, two wire specimens were abraded against each other cyclically while submersed in water at 37°C. Applied forces ranged from 0.05 N to 0.5 N, cyclic motion amplitudes ranged from 0.2 to 2 mm, and test frequencies ranged from 1 Hz to 30 Hz. The analysis demonstrated increasing wear rates normalized to linear distance traveled with increasing normal force, however the relationship between total wear and the test inputs was nonlinear.