title: A model to quantify encrustation on ureteric stents, urethral catheters and polymers intended for urological use.
abstract: OBJECTIVE
  To validate an encrustation model and to quantify encrustation on currently used urological devices and polymers intended for urological use. Materials and methods An encrustation model was validated: (i) to measure the amount of calcium leaching from the glass model and from the polymer used; (ii) to determine whether the use of a single-source or pooled urine produced similar results; (iii) to determine in vitro encrustation; and (iv) to compare the results of in vivo implantation of the same materials into the bladders of rodents with the in vitro results. A test polymer (a ureteric stent, a urethral catheter or a biomaterial) and a control silicone polymer were housed separately but received human urine from the same reservoir and under the same conditions (pH 6.0 and 37 degrees C) for 5 days. The amount of calcium encrustation on each polymer was measured using atomic absorption spectroscopy. Each experiment was repeated at least four times and the results expressed as an encrustation index, defined as the ratio of encrustation of the test and reference polymers.
  
  
  RESULTS
  The amount of calcium leaching from the glass model and polymers tested was insignificant. The use of a single-source or pooled urine gave the same results in the encrustation model. The in vitro results correlated with in vivo implantation of disks into the bladders of rats. Among the commonly used ureteric stents tested, the Cook C-Flex ureteric stents encrusted least. Hydrogel-coated ureteric stents encrusted more than uncoated stents. The Bard polytetrafluoroethylene short-term urethral catheter encrusted more than the Bard hydrogel-coated long-term catheter. A plasma-activated surface modification of a synthetic biomaterial with hyaluronic acid encrusted less than silicone, a long-term biomaterial widely regarded as the 'gold standard'.
  
  
  CONCLUSIONS
  This validated encrustation model is the first to quantify encrustation on currently available ureteric stents and urethral catheters. A novel coating for a biomaterial was identified using the encrustation model, and which encrusted less than silicone.
authors.affiliation: Institute of Urology and Nephrology, London, UK. simon@choong.demon.co.uk
authors.forename: S K
authors.initials: SK
authors.lastname: Choong
authors.forename: S
authors.initials: S
authors.lastname: Wood
authors.forename: H N
authors.initials: HN
authors.lastname: Whitfield
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003460:Crystallization; D004866:Equipment Contamination; D006801:Humans; D011108:Polymers; D051381:Rats; D015607:Stents; D014546:Urinary Catheterization; D014556:Urine
chemical_list: D011108:Polymers; D002118:Calcium