In vitro encrustation of a semi-permanent polymer-covered nitinol ureter stent: an artificial urine model

To measure and compare the percentage of surface and luminal thickness of encrustation in Allium and conventional double J ureteric stents after exposure for 6 weeks to an accelerated encrustation model.

An artificial urine solution was prepared and three stents were immersed into each of six containers allocated to each stent type, representing each week of encrustation. Slight agitation was accomplished by placing a magnetic stirrer at the bottom of each container. Images were obtained by examination under a stereomicroscope and analyzed with the aid of specialized image analysis software (Image J).

By week 2, nearly 100 % of the stent surface was covered by a thin layer of encrustation, gradually increasing in thickness through weeks 3-6. On completion of 6 weeks of encrustation, the 10 mm length double J stent specimens did not show visible encrustation, while the 60 mm long Allium stents showed 100 % surface coverage. This was most evident in the mid-section of the stents compared to the ends, suggesting a correlation between stent length and encrustation formation. There was also no blockage of the lumen of either stents between weeks 1-6.

The designed accelerated encrustation model was successful and showed 80 % surface coverage after 6 weeks. In our study, there appears to be a slightly reduced level of surface encrustation to that of earlier reports. A correlation between stent length and geometry was suggested. This model may be used to compare encrustation for a variety of polymeric stent materials.