Particle Accumulation in Ureteral Stents Is Governed by Fluid Dynamics: In Vitro Study Using a "Stent-on-Chip" Model

Abstract

Objective: To investigate the correlation between fluid dynamic processes and deposition of encrusting particles in ureteral stents.

Materials and methods: Microfluidic models (referred to as "stent-on-chip" or SOC) were developed to replicate relevant hydrodynamic regions of a stented ureter, including drainage holes and the cavity formed by a ureteral obstruction. Computational fluid dynamic simulations were performed to determine the wall shear stress (WSS) field over the solid surfaces of the model, and the computational flow field was validated experimentally. Artificial urine was conveyed through the SOCs to measure the temporal evolution of encrustation through optical microscopy.

Results: It was revealed that drainage holes located well downstream of the obstruction had almost stagnant flow and low WSS (average 0.01 Pa, at 1 mL/min), and thus suffered from higher encrustation rates. On the contrary, higher levels of WSS in holes proximal to the obstruction (average ∼0.04 Pa, at 1 mL/min) resulted in lower encrustation rates in these regions. The cavity located nearby the obstruction was characterized by high levels of encrustation, because of the low WSS (average 1.6 × 10^-4 Pa, at 1 mL/min) and the presence of flow vortices. Increasing the drainage flow rate from 1 to 10 mL/min resulted in significantly lower deposition of encrusting crystals.

Conclusion: This study demonstrated an inverse correlation between deposition of encrusting bodies and the local WSS in a stented ureter model. Critical regions with low WSS and susceptible to encrustation were identified, including "inactive" side holes (i.e., with minimal or absent flow exchange between stent and ureter) and the cavity formed by a ureteral occlusion. Findings from this study can open new avenues for improving the stent's design through fluid dynamic optimization.

Keywords: encrustation; flow dynamics; microfluidic; side holes; ureter; ureteral stent.