Material properties of urethral stents for hypospadias repair

Abstract

Introduction: Despite the prevalence of hypospadias surgery and the near ubiquitous use of postoperative urethral stents, there has been no evaluation of the material properties of commonly used choices. Our study sets out to close this gap with an evaluation and comparison of the material properties of four urethral stents commonly used after hypospadias surgery. Study Design: Thermal analysis and mechanical analysis of the Zaontz Urethral Stent, the Firlit-Kluge Urethral Stent, the Koyle Diaper Stent, and the Bard Premature Infant Feeding Tube were performed. Results: Thermal analysis shows that all four compositions tested are rubbery polymers at body temperature, with glass transition temperatures far below human body temperatures. The Zaontz and Koyle stents are thermoplastic elastomers with strong melting transitions above body temperature, but the Firlit-Kluge stent is completely amorphous at body temperature and is likely chemically cross-linked to generate the polymer network. The Bard feeding tube was by far the stiffest, with a Young's Modulus of 14.0±0.78 (compared to the Zaontz stent at 4.12±0.56, the Firlit-Kluge stent at 4.92±0.63, and the Koyle stent at 4.09±0.49.) The Firlit-Kluge stent was the strongest, with 84.3±2.83 MPa required to fracture it compared to the Zaontz stent at 65.5±2.57, the Koyle stent at 66.8±3.16, and then Bard feeding tube at 34.6±1.89. Discussion: While there is little information associating urethral stent type with outcomes after hypospadias surgery, material properties may account for findings of prior studies. Stiffer stents may contribute to decreased postoperative comfort, while a stent that is too soft and extensible may have issues with dislodgement, kinking and breaking. Conclusion: This study provides a foundation for future work optimizing urethral stents, designing support for regenerative medicine applications, and improving hypospadias outcomes.