Fluid mechanical performance of ureteral stents: The role of side hole and lumen size

Abstract

Ureteral stents are indispensable devices in urological practice to maintain and reinstate the drainage of urine in the upper urinary tract. Most ureteral stents feature openings in the stent wall, referred to as side holes (SHs), which are designed to facilitate urine flux in and out of the stent lumen. However, systematic discussions on the role of SH and stent lumen size in regulating flux and shear stress levels are still lacking. In this study, we leveraged both experimental and numerical methods, using microscopic-Particle Image Velocimetry and Computational Fluid Dynamic models, respectively, to explore the influence of varying SH and lumen diameters. Our results showed that by reducing the SH diameter from 1:1 to 0:4 mm the median wall shear stress levels of the SHs near the ureteropelvic junction and ureterovesical junction increased by over 150%, even though the flux magnitudes through these SH decreased by about 40%. All other SHs were associated with low flux and low shear stress levels. Reducing the stent lumen diameter significantly impeded the luminal flow and the flux through SHs. By means of zero-dimensional models and scaling relations, we summarized previous findings on the subject and argued that the design of stent inlet/outlet is key in regulating the flow characteristics described above. Finally, we offered some clinically relevant input in terms of choosing the right stent for the right patient.

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

“…By summarizing all the studies that reported WSS values at different locations of the ureteral stent in Table 2, our intention is to provide valuable insights into the fluid dynamics of the stent. The findings reveal that the proximal side holes exhibit WSS values below 0.001 Pa (2,33), indicating relatively low to moderate fluid shear forces in this region. The WSS increases toward the middle side holes, with values ranging from the order of 0.0001 Pa up to 0.1 Pa (2, 33), suggesting a notable enhancement in fluid shear stress.…”

“…Ureteral stents are indwelling medical devices commonly used to maintain the patency of the obstructed ureter to preserve/restore urine flow from the kidney to the bladder (1). A typical ureteral stent is a thin-walled polymeric tube with a length of 20-30 cm and an outer diameter ranging from 1.60 mm to 2.67 mm (2). A stent is equipped with small circular openings, known as side holes, that are often positioned throughout its length, allowing exchange of flow.…”

“…In parallel to stent coatings and materials, fluid dynamicsdriven design is an active research area that is being pursued with the aim of reducing encrustation and biofilm formation in stents. Some studies focused on fluid mechanical changes due to different stent sizes (2,(21)(22)(23), and the diameter (2,14) and spatial distribution (24,25) of side holes using mathematical modeling (26)(27)(28), computational fluid dynamics (CFD) (21)(22)(23)(24)(25)(29)(30)(31), and in vitro flow systems (2,14,22). However, only a limited number of studies have analyzed the interplay between flow metrics (such as WSS), crystal deposition (14, 32, 33) and bacterial attachment (34) within a stented ureter.…”

“…Finally, it identifies a range of WSS values acting on the stent surface and elucidates the impact of WSS on biofilm formation and crystal deposition. 2 The dual threats: microbial colonization and encrustation…”

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

“…The in vitro model consisted of three components, the ureter model ( Zheng et al, 2022a ), the bladder model, and the urethra model. The ureter model was made by silicone molding, and was 270.6 mm long with a 4 mm inner diameter, including two conical ends to simulate the ureteropelvic junction (UPJ) and UVJ ( Figure 1A ).…”