Comparison of Mechanical Deformation Properties of Metallic Stents with Use of Stress-Strain Analysis

Elastic and plastic deformation properties of the Wallstent, Palmaz stent, and Strecker stent were evaluated quantitatively with an in vitro model simulating forces exerted by an eccentric lesion. A miniaturized compression testing device was constructed. Stress-strain graphs were obtained for each stent, and the elastic moduli and yield points were calculated. There is a 21-fold range in the elastic modulus among the Wallstent, Palmaz stent, and Strecker stents. The Palmaz stent was the only device to exhibit permanent plastic deformation. The 10-mm Palmaz stent will undergo 15% focal eccentric narrowing at 0.75 atm of pressure; the “standard braid” and “less shortening braid” 10-mm Wallstents at 0.55 and 0.25 atm, respectively; and the 10-mm tantalum Strecker stent at 0.08 atm. Overlapping of stents doubles the stiffness of the Wallstent and the Strecker stent and doubles the yield point of the Palmaz stent. The 4–9-mm Palmaz stent is 30% more resistant to deformation than the larger 8–12-mm version when expanded to identical 8-mm diameters. The “standard braid” version of the 10-mm Wallstent provides 2.3-fold additional strength for resistant stenoses compared with the “less shortening braid.” Overlapping or nesting of stents may permit full expansion should there be incomplete expansion or recoil of a single stent. The 4–9-mm Palmaz stent is preferable from the standpoint of allowing the use of a smaller (7-F instead of 9-F) introducer sheath and also for providing superior resistance to deformation. A purely elastic stent such as the Wallstent is preferable in locations where permanent plastic deformation may occur, such as the thoracic outlet.