Slippery when wet: The effect of a novel zwitterionic coating on silicone ureteral stents

Silicone ureteral stents provide anti-encrustation properties and patient comfort but are more difficult to insert and remove due to increased surface friction. Applying zwitterionic coatings to silicone stents may reduce friction and facilitate stent placement and removal. This study compared the frictional forces of zwitterionic-coated silicone stents with commercial stents using benchtop models. The static and kinetic frictional forces of five ureteral stents were measured: bare silicone stent without coating (BS), single outer-coated zwitterionic silicone stent (Z1), double-coated (inner and outer) zwitterionic silicone stent (Z2), Black Silicone Filiform stent ("Black Beauty") (BB), and Universa Soft stent (US). Friction was assessed with a submerged guidewire model to isolate stent-guidewire friction and a porcine ureteral model to simulate intraoperative stent insertion and removal. Five trials per stent were performed using a force gauge integrated with an Arduino-controlled motor system. Statistical significance was assessed using linear mixed-effects models with stent type and trial as fixed effects and ureter specimen as a random intercept. Pairwise comparisons were adjusted using the Holm method. In the submerged guidewire model, Z2 had 99%, 47%, and 40% lower kinetic friction than BS, BB, and US, respectively. During stent insertion, Z2 had 71%, 43%, and 44% lower kinetic friction than BS, BB, and US, respectively. During stent removal, Z2 had 92%, 58%, and 60% lower kinetic friction than BS, BB, and US, respectively. Linear mixed-effects models demonstrated a significant effect of stent type for all six friction conditions (all p < 0.001). The double-coated (inner and outer) zwitterionic silicone stent (Z2) demonstrated the lowest frictional forces across all testing conditions. Zwitterionic surface modification may therefore reduce friction during silicone stent placement and removal.