Accelerated fatigue behavior and mechano-physical characterizations of in vitro physiological simulation of nitinol...

In this study, we have provided an experimental evaluation of the fatigue behavior of the nitinol (NiTi) endovascular device (peripheral stent). The accelerated fatigue tests were performed using arterial conditions, which mimicked actual physiological conditions. Natural, rubber latex-tubing materials were used to simulate human arteries. The equipment design and the test parameters used allowed for the simulation of a compliant artery and the application of circumferential forces to the device.The stent compliance values were good indicators for tracking the time evolution of fatigue behavior. Moreover, the analyses of changes on the surface morphology and on the chemical composition were used to establish a relationship between surface characteristics and peripheral stent response during 400 million cycles, which is equivalent to 10 yrs of human life. In order to determine the influence of the accelerated fatigue, an evaluation of both mechanical and surface characteristics was carried out before and after testing using the following tests and methods, respectively: radial hoop testing (RH), scanning electron microscope analysis (SEM), auger electron spectroscopy (AES), atomic absorption spectroscopy (AAS), and X-ray photoelectron spectroscopy (XPS). Under these experimental conditions, the studies have shown that after 400 million cycles, the tested stents did not demonstrate any mechanical failure. Moreover, the surface did not undergo any changes in its chemical composition. However, we did observe an increase in roughness and signs of pitting corrosion.