The distribution of crystalline material in obstructed stents--in need for intra-luminal surface modification?

PURPOSE: Usually, hampered urine flow and failing of Seldinger technique leads to the explanation "obstructed ureteral stent" with no further clarification where exactly the obstructions are located. If stent obstruction is caused by intra-luminal biofilm and/or crystal deposits, the need of biofilm reducing coatings on the stent's inside has to be discussed. MATERIALS AND METHODS: We investigated 59 stents from patients in whom acute hydronephrosis and/or acute pyelonephritis required stent replacement and/or usage of Seldinger technique failed. The stents were investigated by X-ray and, after longitudinal cutting, by light-microscopy for occurrence of obstructing material. RESULTS: The inside of 25% of the samples was lined with a thick film composed of blood clots and tiny non-aggregated crystals. Only in these samples X-ray investigation showed a positive result for massive inner encrustations, which in fact may be responsible for stent occlusion. 48% of the stents contained few small domains composed of blood clots and crystals. 27% of the stent samples showed no alteration. CONCLUSIONS: 75% of the "obstructed" stents showed no significant inner deposits. Obstruction of urine transport and failure of Seldinger technique occurred due to other reasons. Thus, coating of the stent's inner surface may be overrated.

Diamond-like carbon coatings on ureteral stents--a new strategy for decreasing the formation of crystalline bacterial biofilms?

PURPOSE: Any catheter material placed in the urinary tract provides a surface for bacterial colonization and, therefore, it is susceptible to encrustation with crystalline bacterial biofilm. Encrustation and blockage by biofilms remain a major complication in patient care. Most patients with indwelling ureteral stents experience irritative symptoms related to these implants and many experience discomfort. MATERIALS AND METHODS: Plasma deposited diamond-like amorphous carbon coatings are well-known for their excellent biocompatibility. A low temperature, low pressure plasma enhanced chemical vapor deposition technology was developed especially for coating polymeric medical implants with diamond-like carbon. We investigated the ability of diamond-like carbon to decrease the formation of crystalline bacterial biofilm as well as stent related side effects and discomfort. Diamond-like carbon coated ureteral Double-J stents were tested in vivo. RESULTS: In 10 patients with heavy encrustation, different underlying diseases and a stent removal frequency of less than 6 weeks due to encrustation a total of 26 diamond-like carbon coated stents were successfully tested for their ability to decrease the extent of crystalline biofilm formation. There was a 2,467-day period of experience with diamond-like carbon coated stents. No primarily stent related complications occurred. No crystalline biofilm formation was observed in vivo. Excellent and facile handling, a less painful replacement procedure and high tolerance of application were reported by physicians and patients. Due to low friction the coated stents could be placed and removed much more easily than standard stents. The frequency and severity of symptomatic urinary tract infections were distinctly decreased. CONCLUSIONS: Diamond-like carbon coating is a new strategy to improve the surface properties of ureteral stents. This novel surface effectively decreases friction, encrustation tendencies and biofilm formation.