Strength, elasticity, and plasticity of expandable metal stents: in vitro studies with three types of stress.

PURPOSE

Five types of expandable metal stents (Palmaz, Strecker, Gianturco, Cragg, and Wallstent) were subjected to standardized tests to obtain objective, comparable data of their mechanical characteristics.

MATERIALS AND METHODS

The stents were subjected to area loads, point loads, and circular loads; the resistance of the stents to a continually increasing deformation was measured. Elasticity and deformation characteristics of the stents were also noted. Another experiment simulated the situation of the stent in an implanted state. The stents were covered with a thin self-adhesive foil to simulate optimal wall contact by limiting the mobility of the mesh struts.

RESULTS

For all types of stress, the Palmaz stent showed the highest resistance but was completely inelastic. The Strecker stent and the Wallstent showed higher resistance when coated in foil (simulating good wall contact). The Gianturco stent showed the lowest resistances but was completely elastic. A point load on a Wallstent caused concentric constriction over a longer distance.

CONCLUSIONS

Palmaz stents are appropriate for insertion into highly resistant obstructions. Strecker stents and Wallstents require good wall contact to achieve adequate strength. Because of their unique deformation characteristics, Wallstents may not function well if implanted into eccentric stenoses of tough consistency. The Gianturco stent showed the lowest resistances.