Evaluation of Nitinol Stents Using a 3-Dimensional Printed Superficial Femoral Artery Model: A Preliminary Study

Mechanical tests assessing Nitinol stents used for the superficial femoral artery (SFA) are designed without taking into account their deployment environments. The objectives of this study were (1) to create normal and pathologic femoral artery models, (2) to run mechanical tests reproducing the stresses of the SFA, and (3) to study and compare Nitinol stents in those conditions.

Femoral artery models with identical mechanical properties to the SFA were created using the 3-dimensional printing technology. Those models were designed with and without an asymmetric focal 50% stenosis. Three mechanical tests (bending-compression, bending-compression-torsion, and multiple bending tests) were created and 1 flexible stent was tested, of 6 and 7-mm diameter. Three samples of the stent, LifeStent (Bard(®)), were deployed and tested in the models. Stents alone were evaluated in the same conditions. The analysis focused on the comparison of rheologic curves, level of kink, and the energy deployed for each stent to kink.

In the 3 tests, all stents deployed in the models presented a kink during their evaluation. When tested alone, during the compression-bending and bending-compression-torsion tests, no plicature was observed. During the multiple bending test, the energy deployed to plicature for the stent tested alone was of 1.4 ± 0.10 and 2.84 ± 0.1 J compared with 9.7 ± 0.6 and 8.25 ± 0.6 J when deployed in the model for the Lifestent 6 × 80 and 7 × 80 mm, respectively. For all of these 3 tests, 6-mm diameter stents exhibited a level of kink and energy of kink higher than 7 mm stents. The behavior of the stents changed in the stenosed model whatever diameter is taken into account. Analysis of the rheologic curves showed a decrease in the inflection of the curve related to the plication. In the bending-compression test, the presence of a stenosis lead to an early plication of the model, with less deployed kinking energy whereas in the bending, compression, and torsion test, this earliness was absent.

This study permitted the creation of a mechanical test platform evaluating Nitinol stents in bending situations. It tends to confirm the mechanical deleterious effect of excessive oversizing. This study confirms the necessity to evaluate Nitinol stents in their deployment environments.