Resistance to hoop stress in balloon expandable stents: evaluation in an ex vivo model.

Abstract

To develop a new model for a more realistic evaluation of radial strength and elastic recoil of balloon expandable stents using a new ex vivo model in human cadaver bifurcations of the aorta. Four different stents (each group n = 10) were implanted in cadaver common iliac arteries. Randomization was performed either to right or left iliac artery. The specimens were cast filled with silicone caoutchouc and after 24 hours the vascular walls including the stents were removed from the hardened casts. The weight of the cast cylinders of the stents was measured in air and in purified water: the difference of the two values resulted in the buoyancy force and because of that the volume of the bodies as a relative degree for the radial strength could be calculated. The findings were correlated with the workbench tests of the manufacturers. Manufacturer's workbench tests were incomparable because of wide spread specifications. There was a significant difference between the theoretical maximal volume (0.866 mL) and the real cast volumes ( P< 0.025) that corresponds directly to the elastic recoil of the stents. The following mean real cast volumes were measured (corrected for 1 cm): Sinus-Stent 0.677 mL, Palmaz-Stent 0.708 mL, Jostent 0.715 mL, Saxx-Stent 0.732 mL, thus reflecting the various degree of radial strength; therefore, the ranking in radial strength resistance was Saxx, Jostent, Palmaz, and Sinus. High radial strength and low elastic recoil are important requirements of any stent design. Ex vivo tests unlike in vitro physical testing facilitate a realistic evaluation of the inherent stent characteristics. The model used in this study proved to be uniformly valid for physical stent design testing.