In vivo evaluation of the third generation biodegradable stent: a novel approach to avoiding the forgotten stent syndrome.

PURPOSE: Ureteral stents are prone to irritation, encrustation and infection, and they require additional procedures for removal. Furthermore, indwelling polymer stents are often forgotten with devastating consequences to the patient. We describe the degradation time, and physiological and histological responses elicited by a novel biodegradable ureteral stent in a porcine model. MATERIALS AND METHODS: A total of 16 female Yorkshire pigs were used in the study. Ten biodegradable Uriprene™ stents and 6 biostable Polaris™ stents were cystoscopically inserted unilaterally in 2 groups of animals. Excretory urogram, and blood and urine tests were performed on different days until day 28. Biostable stents were removed on day 21. On day 28 all pigs underwent necropsy for microscopic and histological evaluation. RESULTS: Nine of the 10 biodegradable stents (90%) degraded completely by 4 weeks, while 1 pig had 3 fragments smaller than 1.5 cm in the bladder. Excretory urogram showed equivalent drainage and significantly less hydronephrosis in biodegradable stented kidneys. Blood and urine parameters were similar in the 2 groups. A transient increase in serum creatinine on day 7 in 40% of the pigs with a degradable stent resolved by day 10. There were significantly fewer abnormal histological findings in the degradable stent group. We evaluated drainage characteristics in an unobstructed ureter and results may not be representative of what develops in obstructed ureters. CONCLUSIONS: The third generation biodegradable stent is a safe, effective alternative to conventional polymer stents, resulting in equivalent drainage and less hydronephrosis.

Next generation biodegradable ureteral stent in a yucatan pig model.

PURPOSE: Ureteral stents are commonly used to facilitate kidney drainage but they may produce significant stent symptoms and morbidity, and require a secondary procedure for removal. Previous biodegradable stents showed bio-incompatibility or inconsistent degradation, requiring extra procedures to remove undegraded stent fragments. We previously reported a first generation biodegradable stent composed of suture-like material that required placement through the lumen of a sheath and degraded by 10 weeks. We now report second and third generation biodegradable stents that degrade more rapidly and can be placed directly over a polytetrafluoroethylene guidewire. MATERIALS AND METHODS: Two groups of 16 Yucatan pigs each were unilaterally stented endoscopically with a control nondegradable (biostable) stent or a second generation degradable Uriprene stent. Blood studies, renal ultrasound and excretory urography were done throughout the study to determine renal function, hydronephrosis and stent degradation. Genitourinary organs were harvested at necropsy for pathological analysis. A third generation stent designed to improve degradation time was bilaterally implanted endoscopically into 4 Yorkshire Farm pigs (total of 8 stents), followed by excretory urography weekly to assess degradation and kidney function. Biomaterial parameters were tested. RESULTS: Second generation stents began degrading at 2 weeks and were completely degraded by 10 weeks. All third generation stents were degraded by 4 weeks. Hydronephrosis was considerably less in the Uriprene group than in control biostable stented kidneys. Biostable stented ureters showed an average higher degree of inflammation, uropathy and nephropathy. Physical characteristics indicate that Uriprene stents are significantly more resistant to stent compression and have markedly higher tensile strength and coil strength comparable to that of other commercially available plastic stents. CONCLUSIONS: Our study confirms that Uriprene stents are biocompatible and provide good renal drainage. They hold promise for decreasing the need for a secondary procedure and stent related morbidity, such as infection and irritative symptoms.

Investigation of a novel degradable ureteral stent in a porcine model.

PURPOSE: Ureteral stents often result in patient morbidity and the potential for a forgotten stent. When the suture tether is detached, a secondary procedure is required for removal. Previous attempts at developing biodegradable ureteral stents have been unsuccessful since those stents were not biocompatible or they failed to degrade in timely fashion. We evaluated a new biodegradable Double-J stent in a porcine model. MATERIALS AND METHODS: A total of 36 Yorkshire pigs were stented unilaterally with a biodegradable Uriprene stent or a standard biostable control stent. Excretory urograms, and blood and urine tests were performed at weeks 2, 3, 4, 5, 7 and 10. Four animals per group were sacrificed after 2, 4, 7 and 10 weeks to determine stent degradation and obtain samples for pathological evaluation. RESULTS: Degradable ureteral stents began to degrade at 3 weeks. By weeks 7 and 10, 60% and 100% of the stents, respectively, were fully degraded. There was no significant difference in laboratory parameters or the amount of hydronephrosis between the 2 groups. However, ureteral dilatation was significantly more pronounced in the control group than in the Uriprene group. The novel stent was biocompatible on histological evaluation and it led to significantly less urinary tract infections than in controls. CONCLUSIONS: The novel Uriprene stents provided drainage similar to that of regular stents and they were completely degraded by 10 weeks. Moreover, these stents resulted in less ureteral dilatation and fewer positive urine cultures. Biocompatibility was good and human trials will be forthcoming.