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 singlesource 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 37uC) 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, de®ned 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 insigni®cant. 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 polytetra¯uoroethy-lene short-term urethral catheter encrusted more than the Bard hydrogel-coated long-term catheter. A plasma-activated surface modi®cation of a synthetic biomaterial with hyaluronic acid encrusted less than silicone, a long-term biomaterial widely regarded as the`gold standard'. Conclusion This validated encrustation model is the ®rst to quantify encrustation on currently available ureteric stents and urethral catheters. A novel coating for a biomaterial was identi®ed using the encrustation model, and which encrusted less than silicone.

An artificial model for studying fluid dynamics in the obstructed and stented ureter

“…Only few studies have attempted to dynamically model ureteric stents exposed to flow in vitro [14]. In this work a biomimetic physical model, closely resembling the real ureter geometry, has been designed based on direct measurements on pig ureters.…”

Enlargement of calcium oxalate stones to clinically significant size in an in‐vitro stone generator

“…These have used artificial urine or human urine in static or continuous-flow systems [19] and usually concentrate on calcium phosphate or magnesium ammonium phosphate mineralization onto a polymer. One method, more pertinent to stone formation, has been described by Söhnel et al [20] in which CaOx was precipitated onto silicate spheres, in a manner which was claimed to be representative of papillary and calyceal stones.…”

A New Biomaterial for Urinary Catheters

“…Which characteristics does it must have? It must be resistant to biofilm formation and bacterial colonization; able to resist encrustation; be biologically inert; have chemical stability when in urine contact; be easy to implant and remove; not prone to migration; allow optimal flow; be sterilizable; durable; radiopaque and low cost [11].…”