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About STONES - Bioengineering Ureteral Stents (BUrSt) Initiative
Our Mission
Our mission is to provide data that supports Silicone Ureteral Stents for patients with Kidney Stones. Learn more about Silicone Ureteral Stents by navigating our website.
Out with the Old, In with the Silicone!
Background
Chronic kidney disease affects about 1 in 7 people in the United States, and the lifetime risk of kidney stones is roughly 10-15%. For patients with kidney stone disease, ureteral stents are often placed to serve as a drainage pipe to allow flow of urine from kidney to the bladder. However, conventional polyurethane stents are prone to failure: calcium can build up over the stent, encrustation, and reduced flow, the stent can lose its coil and migrate into the bladder, and the material can fatigue and fragment within the ureter.
Aims
Design and perform experimental setup to compare Polyurethane and Silicone Ureteral Stents.
1) Characterize ex vivo animal (bovine, porcine) kidneys. Compare anatomy and size to human
2) Performing mechanical testing : friction/coil strength, tensile and compressive stiffness of Ureteral stents pre and post exposure to urine over an indwelling time of 30 days
3) Investigating radiopacity and rate of calcium deposition buildup of ureteral stent
Studies Performed in the BUrSt Initiative
1. Ex-Vivo Models
To accurately test the stents, an environment similar to an adult human urinary system would be ideal to replicate. This means utilizing a model where the stent can sit in a small space, like a ureter, and have coils anchored in the kidney and bladder. In this study we examined samples of the urinary system of an immature Bovine model, and immature Porcine model
Samples of Urinary Systems Used in Study:
Immature Porcine
Immature Porcine
Immature Bovine
Immature Bovine
Dissected Ureter
Porcine Ureter
Bovine Ureter
Kidney Dissections
Porcine
Porcine
Bovine
Bovine
"Calamari Rings" to measure inner diameter attempted for porcine
Results
The average human ureter is approximately 28 to 30 cm in length with an outer diameter of around 2-4mm. Our results of this study found that our bovine sample had a ureter of approximately 16 cm in length and 1.8 mm outer diameter. The porcine model had a length of 31.5 cm with an average outer diameter of about 4 mm. This means the bovine model is about 50% shorter than a human ureter with below average outer diameter, and the porcine model has consistent dimensions to that of a human. For our next study, however, we needed the stent to be able to fully re-coil once inserted into the model kidney. Upon quick observation, we noticed that the model kidney architecture would not allow this, so for the friction and coil strength test, a medium of bologna was used. The results of this study however, indicate that for future studies a porcine model may be viable for ureteral stent studies.
2. Friction/Coil Strength
Experiment
Silicone and polyurethane ureteral stents were pulled through a 2mm drilled holes in a Bologna meat model. Force and displacement were recorded and graphically represented.
Stents used in study were: Cook Medical Black (6Fr silicone), Bard Fluoro (6Fr silicone), Coloplast Stenostent (8Fr silicone), Coloplast Imajin Hydro (6Fr silicone), and Boston Scientific Ascerta (6Fr polyurethane).
Experimental blueprint and setup
Experimental blueprint and setup
Top: Blueprint anticipated setup were illustrated and shows the progression of the stent traveling through bologna with focus on the proximal end.
Bottom: Coil-strength experimental setup with progression moving stent. Movies were made of the stent's progression.
Force & Displacement Pull-Thru Test
Force & Displacement Pull-Thru Test
Force and Displacement results
Maximum forces
Maximum forces
Highest average forces of pulling the stent through were recorded
3. Imaging (Ultrasound, Floroscopy, Micro CT)
Clear visibility of stents allows surgeons to accurately identify and target specific anatomical landmarks, ensuring precise surgical maneuvers and minimizing risk of errors.
Ultrasound Experimental Setup
Fluoroscopy of Stents
Micro-CT Image of Sliced Indwelled Stent from Human
1) Fluoroscopy
1) Fluoroscopy
Fluoroscopy is a diagnostic imaging technique that uses X-rays to obtain real time moving images of the internal structures of body.
2) Ultrasound
2) Ultrasound
Ultrasound uses sound waves to create internal structures of the body, providing a non-invasive and radiation free method.
Ultrasound Image of silicone stent in bladder filled with sterile water
3) Micro CT
3) Micro CT
Micro-CT is an imaging technique that incorporates using X-rays to create slice by slice images of testing region. By using the Micro-CT we are able to evaluate qualitatively the encrustation of a patient indwelled polyurethane stent by cutting the stent into fragments to be placed within a test tube for performing imaging. The sliced image generated for the fragments corresponds to darker regions refer to more encrustation.
To improve the quality of the results attained, placement in vertical orientation in oppose to the horizontal orientation performed is expected to make the visualization of the encrustation easier based on the sliced views for the Micro CT.
We analyzed the commercially available silicone stents and polyurethane stents under C-arm X-ray machine while they are inserted in porcine kidney.
For ultrasound we used porcine bladder to test the echogenicity of the silicone stents and polyurethane stents with the help of butterfly ultrasound probe.
UC San Diego Bioengineering Day Showcase
Publication
MastersCapstone.pdf© 2025 by Sujit Tunuguntla
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