Ureteral stents: Coil strength and durometer

To evaluate the coil strength before and after urine exposure and the stiffness of commercially available double- J ureteral stents because both properties may affect stent performance and patient comfort. Twelve commercially available 6F ureteral stents were tested for coil strength before and after 30 days of urine exposure. The proximal end of each stent was inserted through a 2-mm hole in bologna, allowed to recoil, and then pulled using a handheld force gauge. Ten different commercially available ureteral stent models were tested for tensile strength using an MTS MicroBionix Testing System and Testworks II software and a 5 N load cell. The Cook Black Silicone and Cook C-Flex stents had the strongest coil strengths before urine exposure at 0.480 ± 0.0 lb ( P ≤0.0006) and were also the stents that had the greatest decrease in coil strength after urine exposure. After urine exposure, the weakest stent was the Applied Vertex stent at 0.088 ± 0.008 lb ( P ≤0.02) and the strongest was the Cook Endo-Sof AQ at 0.223 ± 0.014 lb ( P ≤0.03). Calculating the Young’s modulus, E, the Cook C-Flex stent was the stiffest (E = 1472 ± 196 KPa) and the Cook Black Silicone was the least stiff (E = 122 ± 18 KPa). The stent models that demonstrated consistent E values across different lot numbers were the Circon Double J stent and Bard InLay. Ureteral stents can be differentiated according to their coil strength and stiffness. The impact of these properties on stent performance and patient comfort deserve additional evaluation. The significant variability found in stent stiffness among stents from different lot numbers suggests poor quality assurance in biomaterials or stent processing and increases the complexity of cross-stent comparisons.