Ureteral stents implanted in patients' ureters often become obstructed, which has been a clinical challenge. Certain ureteral DJ stents, e.g., Inlay Optima Ureteral Stent (BD), have a special coating on their surface to prevent particle adhesion. However, when implanted in the ureter for a long time, urinary tract infections inevitably occur, and the lumen is likely to be occluded by debris or stones. This study aimed to clarify the obstruction mechanism of ureteral Double J stents implanted in patients.

Obstructed ureteral DJ stents were removed from the patient's body, immediately cut into small pieces, and fixed in 100% ethanol. The ureteral stent specimen was encased in an insulating resin, and the cut and polished thin sections were analyzed by scanning electron microscope(SEM). The specimens were coated with osmium using a low-temperature plasma coating technique that we have developed, which prevents thermal denaturation of proteins and enables precise analysis of pathological specimens. The lumen was ultra-microscopically and elementally analyzed using characteristic X-ray analysis of SEM.

SEM analysis showed that the ureteral stent's surface was suspected to have been detached circumferentially with an adhered layer of Ca phosphate stones. The delaminated stent surface was observed to have additional infected stones, i.e., magnesium ammonium phosphate (MAP) stones, deposited on the outer surface.

These results suggest that the ureteral stent surface was not delaminated during the specimen preparation but spontaneously delaminated with the Ca phosphate stone layer, which was continued by MAP stones' deposition in the patient's urinary tract. The results of this study are essential in elucidating the process of ureteral stent occlusion and suggest that stent surface delamination may be a contributing factor. Additional validation with a larger sample size is ongoing to confirm this theory.