Wire-Based Ureteral Stents: Impact on Tensile Strength and Compression

Abstract

Objectives To evaluate the performance of coil-based ureteral stents in terms of tensile strength and the radial compression force. Methods 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. Results 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). Conclusions 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.