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Accumulation of stent encrustations depends on fluid dynamics: In-vitro study on a stent-on-a-chip model
4th EULIS Meeting Vienna, Austria
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Accumulation of stent encrustations depends on fluid dynamics: In-vitro study on a stent-ona-chip model Eur Urol Suppl 2017; 16(7);e2520
Mosayyebi A. 1 , K. Somani B. 2 , Zhang X. 3 , Manes C. 4 , Carugo D. 3 1
University of Southampton, Faculty of Engineering And The Environment, Southampton, United Kingdom, 2University of Southampton,
Southampton General Hospital, Southampton, United Kingdom, 3University of Southampton, Faculty of Engineering and the Environment, Southampton, United Kingdom, 4Politecnico Di Torino, Dept. of Environment, Land and Infrastructure Engineering, Turin, Italy Introduction & Objectives: Ureteral stents are one of the most common approaches in retrieving the urine drainage from kidney towards the bladder for blockages or treatment related to kidney stone disease (KSD). Although stents are useful, they are prone to encrustations and biofilm formation leading to blockages and infections. Regardless of the works that have been done on stent material, coatings and designs, fluid dynamics related to stent use has been less well studied. Our study investigates the role of fluid dynamics on formation and growth of stent encrustations. Material & Methods: Artificial urine was conveyed through stent-on-chip models replicating segments of stented ureter in varying physiologically relevant flow rates. Three-dimensional (3D) computational fluid dynamic (CFD) simulations were performed to characterize the flow field within both occluded and unoccluded stented ureters and validated experimentally using a microfluidic-based model of the stented ureter. Bright field microscope images of encrusting deposits were acquired at selected locations using a CCD camera and the size of encrusting bodies was quantified from the acquired microscope images using an image processing routine. Results: In an unoccluded stented ureter there was only minimal fluid exchange between the intra- and the extra-luminal compartments of the stent. This resulted in low fluid velocity magnitude and shear stress relating to the stent side holes, the regions characterised by accumulation and rapid growth of encrusting deposits in the experiments. In an occluded stented ureter, fluid exchange was limited to the first hole post-occlusion, whilst the other holes acted as stagnation regions and therefore suffered from larger and rapidly growing encrustations. Moreover, vortical flow was observed in the fluid cavity of the ureter formed by a complete occlusion of its lumen, causing enhanced trapping of encrusting deposits. However, increasing the total flow rate reduced size and growth rate of encrustation. Conclusions: A direct correlation between fluid velocity magnitude, shear stress and formation/growth of encrusting deposits in ureteric stents was observed. Notably, large majority of the stent side holes which are usually designed to maintain urine drainage, acted instead as primary sites for encrustation. Results from this study may guide the design of smart stent architectures capable of minimising the impact of encrustation.
Eur Urol Suppl 2017; 16(7);e2520
52
Accumulation of stent encrustations depends on fluid dynamics: In-vitro study on a stent-ona-chip model Eur Urol Suppl 2017; 16(7);e2520
Mosayyebi A. 1 , K. Somani B. 2 , Zhang X. 3 , Manes C. 4 , Carugo D. 3 1
University of Southampton, Faculty of Engineering And The Environment, Southampton, United Kingdom, 2University of Southampton,
Southampton General Hospital, Southampton, United Kingdom, 3University of Southampton, Faculty of Engineering and the Environment, Southampton, United Kingdom, 4Politecnico Di Torino, Dept. of Environment, Land and Infrastructure Engineering, Turin, Italy Introduction & Objectives: Ureteral stents are one of the most common approaches in retrieving the urine drainage from kidney towards the bladder for blockages or treatment related to kidney stone disease (KSD). Although stents are useful, they are prone to encrustations and biofilm formation leading to blockages and infections. Regardless of the works that have been done on stent material, coatings and designs, fluid dynamics related to stent use has been less well studied. Our study investigates the role of fluid dynamics on formation and growth of stent encrustations. Material & Methods: Artificial urine was conveyed through stent-on-chip models replicating segments of stented ureter in varying physiologically relevant flow rates. Three-dimensional (3D) computational fluid dynamic (CFD) simulations were performed to characterize the flow field within both occluded and unoccluded stented ureters and validated experimentally using a microfluidic-based model of the stented ureter. Bright field microscope images of encrusting deposits were acquired at selected locations using a CCD camera and the size of encrusting bodies was quantified from the acquired microscope images using an image processing routine. Results: In an unoccluded stented ureter there was only minimal fluid exchange between the intra- and the extra-luminal compartments of the stent. This resulted in low fluid velocity magnitude and shear stress relating to the stent side holes, the regions characterised by accumulation and rapid growth of encrusting deposits in the experiments. In an occluded stented ureter, fluid exchange was limited to the first hole post-occlusion, whilst the other holes acted as stagnation regions and therefore suffered from larger and rapidly growing encrustations. Moreover, vortical flow was observed in the fluid cavity of the ureter formed by a complete occlusion of its lumen, causing enhanced trapping of encrusting deposits. However, increasing the total flow rate reduced size and growth rate of encrustation. Conclusions: A direct correlation between fluid velocity magnitude, shear stress and formation/growth of encrusting deposits in ureteric stents was observed. Notably, large majority of the stent side holes which are usually designed to maintain urine drainage, acted instead as primary sites for encrustation. Results from this study may guide the design of smart stent architectures capable of minimising the impact of encrustation.
Eur Urol Suppl 2017; 16(7);e2520