COMPARISON OF MECHANICAL DEFORMATION PROPERTIES OF METALLIC STENTS WITH USE OF STRESS-STRAIN ANALYSIS

PURPOSE: 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. MATE RIALS AND METHODS: A miniaturized compression testing device was const ructed. Stress-strain graphs were obtained for each stent, and the ela stic moduli and yield points were calculated. RESULTS: There is a 21-f old range in the elastic modulus among the Wallstent, Palmaz stent, an d Strecker stents. The Palmaz stent was the only device to exhibit per manent plastic deformation. The 10-mm Palmaz stent will undergo 15% fo cal 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. Over lapping of stents doubles the stiffness of the Wallstent and the Strec ker 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 CONCLUSIONS: The ''standard braid'' version of the 10-mm Wallstent provides 2.3-fold a dditional strength for resistant stenoses compared with the ''less sho rtening braid.'' Overlapping or nesting of stents may permit full expa nsion should there be incomplete expansion or recoil of a single stent . The 4-9-mm Palmaz stent is preferable from the standpoint of allowin g the use of a smaller (7-F instead of 9-F) introducer sheath and also for providing superior resistance to deformation. A purely elastic st ent such as the Wallstent is preferable in locations where permanent p lastic deformation may occur, such as the thoracic outlet.