G. Siekmeyer, M. Hientzsch, U. Bayer, A. Schuessler, ADMEDES SCHUESSLER GmbH, Pforzheim, Germany
New clinical applications for Nitinol materials such as heart valves, frames or stents for the superficial femoral artery (SFA) expand the market for stent-like components. At the same time the mechanical and fatigue durability requirements increases significantly for current and future medical implants. In the last years a significant number of investigations have been performed to understand the fatigue behaviour of Nitinol, but only limited data exists to predict the fatigue performance by exploring the combination of different tube drawing processes and ingot materials. Nitinol tubes with the same dimensions from different tube drawing processes and ingot materials have been studied by micro dog-bone testing during low cycle/high stress and medium cycle/low stress 2- and 3-point bending testing (with and without initial load). Fatigue test results, data on microstructure, SEM images before and after testing will be presented to identify the preliminary cause for fractures. Correlation between the tests and mechanical data from tensile testing will be reviewed. Observations and the possible indicators for variations in fatigue performance will be discussed.
While true clinical benefit is difficult to ascertain in any in-vitro test method set-up, micro dog-bone testing is a fast and reliable indicator that can assist in differentiating superior from questionable Nitinol tube materials for the manufacturing of stents and stent-like components. Additionally, from our data a decision matrix will be provided as a guide in identifying appropriate markers for the predicted fatigue resistance.
Summary: Nitinol tubes with the same dimensions from different tube drawing processes and ingot materials have been studied by micro dog-bone testing during low cycle/high stress and medium cycle/low stress. Fatigue test results, data on microstructure, SEM images before and after testing will be presented. Correlation between the tests and mechanical data from tensile testing will be reviewed.
