Wire-based ureteral stents: impact on tensile strength and compression

To evaluate the performance of coil-based ureteral stents in terms of tensile strength and the radial compression force.

Three Cook Resonance (RES) metallic coil stents and three coil-reinforced Applied Medical Silhouette (SIL) ureteral stents were tested. An MTS MicroBionix Testing System using Testworks II software, vibration isolation table, and 5-N load cell were used to measure tensile and compressive strength. Stents were placed in hydraulic grips spaced 24 cm apart and stretched at a rate of 5 mm/s for 1 second under uniaxial tension. Extrinsic compression was exerted in 0.2-mm increments to maximum compression. The Young's modulus, E, was calculated for each trial using the engineering stress. Comparisons were made with the Cook C-flex, which in previous studies was shown to be stiffer and more resistant to compression than other traditional polymer stents.

The RES and SIL stents demonstrated tensile strengths of 936 +/- 485 kPa and 770 +/- 82 kPa, respectively (P = 0.02). The elastic modulus required to cause extrinsic compression was lower for the RES (63,248 +/- 3218 Pa) than for the SIL (105,664 +/- 11,529 Pa) (P <0.001). Both stents were more resistant to stent compression than previously tested stents without coil-reinforcement, the strongest of which was the Cook C-Flex (E = 30,355 +/- 910 Pa; P <0.001).

Both the Cook Resonance and Applied Medical Silhouette stents are more resistant to extrinsic stent compression than ureteral stents that are not coil-reinforced. The Cook Resonance has a higher tensile strength, whereas the Applied Medical Silhouette is more resistant to extrinsic compression.