An in vitro bladder model with physiological dynamics: Vesicoureteral reflux alters stent encrustation pattern

Abstract

In vitro models are indispensable to study the physio-mechanical characteristics of the urinary tract and to evaluate ureteral stent performances. Yet previous models mimicking the urinary bladder have been limited to static or complicated systems. In this study, we designed a simple in vitro bladder model to simulate the dynamics of filling and voiding. The physio-mechanical condition of the model was verified using a pressure-flow test with different bladder outlet obstruction levels, and a reflux test was performed to qualitatively demonstrate the stent associated vesicoureteral reflux (VUR). Finally, the setup was applied with and without the bladder model to perform encrustation tests with artificial urine on commercially available double-J stents, and the volumes of luminal encrustations were quantified using micro-Computed Tomography and image segmentation. Our results suggest that, VUR is an important factor contributing to the dynamics in the upper urinary tract with indwelling stents, especially in patients with higher bladder outlet obstruction levels. The influence of VUR should be properly addressed in future in vitro studies and clinical analyses.

The interplay between bacterial biofilms, encrustation, and wall shear stress in ureteral stents: a review across scales

“…However, reflux and narrow regions (e.g., UVJ) in the distal segment of the ureter increase the WSS acting on the stent in this region (24). This increase in shear stress possibly contributes to the reduction of encrustation levels in this region compared to the proximal ones, as shown previously (84). Notably, the reported WSS in the distal section of the ureteral stent spans from 10 -2 to 10 -1 Pa.…”

“…To address this issue, discarding the encrustation on the outer surface from the analysis eliminated this bias but represents a limitation of this technique (5). In this context, combining a quantification method with a physiologically relevant in vitro flow model could serve as a testing platform to help identify regions of the stent prone to encrustation and enable testing of new stent materials and designs, as shown by Zheng et al (84). A recent review covers the topic of experimental flow models in greater depth (85).…”

“…The presence and type of comorbidities, in particular, are known to affect encrustation; for example, encrustation of the kidney pigtail is positively correlated with urolithiasis, whereas encrustation of the bladder pigtail has been correlated with urinary tract infections (82). Moreover, it has been reported that VUR could alter the pattern of encrustation (84), and that side holes are one of the regions most prone to deposition of encrusting material (5,15). In this regard, the possibility of developing patient-specific stents should be considered in the future.…”

“…To investigate encrustation in ureteral stents and its correlation with VUR, Zheng et al (84) developed a macroscale in vitro model of the urinary tract with a programmable bladder to mimic the detrusor pressure waveforms during the bladder voiding stage. This was the first physical model of the urinary tract able to mimic reflux from the bladder to the kidney.…”