Characterization Of Stent Structures From Sputter Deposited Nitinol

Free-standing Nitinol stent structures can be commercially manufactured by a new sputter deposition process with a superior fatigue performance of about 1.4% alternating strain over a tested mean strain from 0% to 6% (in 60um thick diamond shape samples). Therefore, sputter deposited material can be applied safely for new medical components and products such as micro-stents and actuators, membranes or stent graft coverings. Detailed knowledge about the interaction between mechanics and fracture trigger mechanisms, however, is pivotal to optimize and tune any design concept. Because sputter deposited Nitinol is free of inclusions and flaws our study objective was to investigate and understand the underlying crack initiation process for the cause of fatigue fracture.

In this study we will present detailed data from static and dynamic mechanical characterizations of stent-structures from tensile, torsion and radial force testing with similar functional Af-temperature (measured by bend and free recovery) to discuss complex load conditions. SEM fracture morphological characterization in more than 100 retrospective analysed fatigue samples over the above mentioned mean strain window (tested by fatigue-to-fracture according to ASTM and pulsatile fatigue) will be used to group the data. Thereafter, this data will be correlated and compared according to a matrix of crack initiation triggers and markers described previously in the literature for standard Nitinol. A weighted matrix based on the number of identified crack initiation processes will be presented to give more insights into this material and it’s mechanical and fatigue behaviour.