Corrosion Behavior of Large Nitinol Stent Structures Produced from Various Tubing Qualities

Stent structures produced from laser-cut Nitinol tubing are a main component of multiple self-expanding implantable device platforms. These applications include peripheral stents, aortic stentgrafts, transcatheter heart valve prostheses, and left atrial appendage closure devices. For these devices, fatigue durability and corrosion resistance are critical to ensure patient safety and device efficacy.

Technical developments in the Nitinol melting process made it possible to bring new material qualities on the market for medical-device grade Nitinol tubing. These new material qualities all aim on improving microcleanliness by reducing number and size of material impurities such as nonmetallic inclusions, which are known to be a trigger for device fatigue failure as well as for initiation of localized corrosion.

In the present study the corrosion behavior of large electropolished Nitinol stent structures produced from four different tubing qualities is studied based on potentiodynamic polarization testing in phosphate-buffered saline at body temperature. For all tubing qualities studied inclusion size distributions are assessed employing quantitative metallography. Corrosion susceptibility is evaluated by determining the breakdown potentials according to ASTM F2129-08.

Corrosion test results are correlated to the various material qualities and discussed in the context of microcleanliness aspects.