Analysis of Nitinol Wire Wear Performance

Braided wire nitinol devices are commonly used to treat a wide range of cardiovascular issues, ranging from vascular stents to occluder devices.  The cyclic loading applied to braided devices from the cardiac rhythm induces not only cyclic strains in the wires, but also motion between the wires at the crossing points.  Although this cyclic motion is known to induce abrasive wear between wires, which can lead to wire fracture, the wear performance of nitinol wire is not well understood.  Therefore, the purpose of this study was to analyze the effects of normal force, range of motion, and sliding velocity on nitinol wear.

Nitinol wire with a nominal diameter of 0.02” was 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 phosphate buffered saline at 37°C.  Cyclic motion amplitudes ranging from 0.2 to 2 mm were analyzed at a range of sliding velocities and normal forces.  The analysis demonstrated increasing wear rates normalized to linear distance traveled with increasing normal force, cyclic motion amplitude, and velocity.