In vitro testing of a novel soft robotic anti-retropulsion device for use during ureteroscopic lithotripsy

Introduction: Retrograde migration of stone fragments (retropulsion) during ureteroscopic lithotripsy increases the need for auxiliary procedures. Currently, available anti-retropulsion devices (ARDs) have limitations (i.e., actuate with high pressure, allow stone fragments and fluid to pass) or are no longer commercially available. We designed a novel soft robotic ARD prototype that occludes larger-diameter ureters with low pressure. Our objective is to fabricate and test this prototype in a validated in vitro ureteral model. Methods: Prototypes were fabricated with Ecoflex™ 00-30 material and actuated with saline. We compared our prototype with a control (no device) and two other ARDs (Stone Cone™ and Accordion™) in an in vitro ureteral model using electrohydraulic lithotripsy (EHL) with cylindrical phantom stones (plaster of Paris) inside an acrylic tube (9.53-mm inner diameter). Performance was assessed using quantified criteria: stone retropulsion (cm), percent weight loss (%), and device migration distance (cm). Results: Fabricated prototypes occluded the in vitro diameter at low pressures of 0.59 ± 0.03 PSI (average ± SD). All ARDs (our prototype, Accordion™, and Stone Cone™) showed significant reductions in stone retropulsion (2.8 ± 0.3 cm, 3.0 ± 0.4 cm, 3.0 ± 0.7 cm, respectively) compared with the control (17.8 ± 3.1 cm). The Stone Cone™ had a significantly higher percent weight loss (58.9 ± 37.6%) compared with our prototype (18.8 ± 27.9%). Device migration distance did not vary significantly among ARDs. Conclusions: We fabricated a novel soft robotic ARD that completely occluded the intended ureteral diameter under low pressure. Our prototype successfully prevented stone retropulsion similarly to two established ARDs in a validated in vitro ureteral model.