Development of an Ad Hoc Procedure for Nitinol Fatigue Characterization for Peripheral Stents

Nitinol stents are nowadays widely used for the treatment of occlusions in peripheral arteries. However, the risk of stent rupture is source of concerns for Nitinol devices: in some recent clinical studies it affects 30% of the patients. The variability of the incidence of this complication suggests that it is due to many correlated aspects: material properties, device design, patient functional anatomy and lifestyle and surgical procedure. Considering that the small dimension of the stent struts as well as the whole procedure for producing the stent may strongly influence the Nitinol performance, it is clear the importance of performing the fatigue tests on the same stent material. On the other hand, because of the strongly non linear behaviour of Nitinol, a complete and accurate characterization of the material fatigue performance would require a large number of tests and consequently a huge time of testing machine use.
In this work we will describe the numerical studies performed for understanding the solicitation conditions which the stent is subjected to after the implantation and the following design and execution of the experimental campaign. The tests were performed on Nitinol specimens derived from the same tubes used for producing a commercial peripheral stent and created following the same procedure used for the device. As a consequence of the small dimension of the specimens also a preliminary design of the experimental test set-up was required. The obtained results allowed a sufficiently accurate characterization of the stent material fatigue behaviour in the range of interest.

The abstract is submitted to the session ""How to test NiTi medical devices" M. Frotscher, CORTRONIK, Germany