Mechanical Properties of Airway Stents

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Abstract
Mechanical properties of currently used airway stents were tested in excised tracheas. Stress—strain tests included measurements of area versus circumferential (pleural) pressure, area versus load (emulating tumor compression), and force as a function of compression. The Dynamic stent showed the highest stability of the tracheal stents, followed by the Nitinol, the Nova, and the Dumon stents. Factors influencing the recoil of endoprostheses are the Young's modulus, wall or wire thickness, length, caliber, and, for silicone stents. Shore A hardness. The stability depends even more on the position of the applied load. Consequently, the length of the stent should exceed the tracheobronchial stricture by 5 mm. Strecker stents and, especially, Gianturco stents show nonlinear behavior in the compression—force test, indicating a high risk of wall perforation during cough. Palmaz stents are the stiffest metal stents but their stability is shape dependent. Once laterally compressed, these nonelastic stents cannot maintain patency. Wallstents respond to cough with unacceptable changes of length. Nitinol stents have pseudoelastic properties, suggesting optimal capability to adapt to luminal changes with minimal impairment of mucosal perfusion. As epithelialization alters the dynamic properties of all naked metal stents, their feasibility for tracheobronchial application is limited.

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