Mechanical Reliability of Implantable Nitinol Drawn Filled Tube (DFT) Wires

Presented by Juan Pablo Garcia, an undergraduate student at Case Western Reserve University and 2021 participant of the ASM Student Speaking Sympoiusm (S3). To learn more about this contest, please visit https://bit.ly/2WXL3WV

Drawn Filled Tubes (DFTs) are a major component in many cardiovascular and neurostimulation leads. These unique structures combine two materials and their properties by inserting a conductive metal core into an outer metal sheath. This work characterizes superelastic Nitinol-platinum DFT wires. The wires were evaluated under fully-reversed, flex bending fatigue that produces a load ratio, R = -1. The data was plotted as cyclic strain versus lifetime and compared to legacy data representing the more common cobalt-chromium DFT wires containing silver cores. Fracture surfaces were imaged and analyzed using scanning electron microscopy and energy dispersive X-ray analysis, respectively. Data from this investigation demonstrates that the fatigue life decreases with increases in the applied cyclic strain and that Nitinol DFT 10% and 30% platinum wires have similar fatigue trends to other DFT compositions. Fracture surface and chemical analyses showed that fatigue failures initiated at nonmetallic inclusions composed of titanium-rich nickel oxides.