Experimental functional analysis of self-expanding stents using a new developed ex vivo model

To modify an ex vivo test procedure for balloon expandable stents as a means to evaluate the mechanical properties of self-expanding stents.

Ten stents each of 7 different stent models measuring 10 mm in diameter (LUMINEXX Vascular Stent/Memotherm-FLEXX Vascular Stent [identical to Bard], Jostent SelfX, Jostent SelfX high radial force [Jomed], sinus-Repo stent, sinus-SuperFlex stent [Optimed], S.M.A.R.T. stent [Cordis], and Easy Wallstent [Boston Scientific]) were implanted in common iliac arteries taken from cadavers (n = 35). They were randomized to either the right or left bifurcation. The vessels were then maintained at 37 degrees C for 24 hours in a special solution that inhibited autolysis, making it possible for the stents to expand. Afterward, they were filled with silicone caoutchouc. After another 24 hours, the vessel walls and stents were removed from the hardened casts. By means of fine analytic measurements, we demonstrated that the volume of a hardened cast formed in the stent cylinder is an indirect but precise measure of the radial force of a stent. Furthermore, using correlation analysis, we examined the relationship between radial force and vessel diameter as well as that between radial force and the degree of arteriosclerosis.

The differences between the actually measured volumes, ie, radial strength, (1 cm stent length) of the various stent models (LUMINEXX/Memotherm-FLEXX: 0.6198 mL +/- 0.1537 mL; Jostent SelfX: 0.6756 mL+/- 0.1298 mL; Jostent SelfX high radial force: 0.6321 mL+/- 0.1817 mL; sinus-Repo stent: 0.5508 mL+/- 0.1485 mL; sinus-SuperFlex stent: 0.6174 mL+/- 0.0953 mL; S.M.A.R.T. stent: 0.5627 mL+/- 0.1270 mL; and Easy Wallstent: 0.5613 mL+/- 0.1019 mL) were not statistically significant (P > 0.05), but the differences to the theoretically possible volumes that we had previously calculated were highly significant (P < 0.05). Correlation and regression analyses demonstrated a significantly stronger relationship between stent volume and vessel diameter than between stent volume and degree of arteriosclerosis.

The modification of our ex vivo model of balloon-expandable stents now makes it possible for researchers to obtain comparable and realistic values for both the radial force and the expansion of self-expanding stents under realistic conditions. Our methods should therefore be employed as an additional procedure to optimize the preclinical evaluation of new stent during certification.