**3. Conclusion**

In the present chapter we have summarized the results from the characterization of uncoated PU, heparin- and DLC-coated PU ureteral stents after indwelling into 59 patients. Field Emission Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Infrared Spectroscopy were used to characterize both inner and outer catheter surfaces.

With these techniques two kinds of deposits were detected at the stent surfaces:


In addition, the thickness of the encrustations was estimated at the stent cross sections.

We have divided the obtained data according to their indwelling time, the unilateral or bilateral indwelling and the patient's tendency to form calculus (stone-former or not).

Concerning the non-stone former patients, the encrustation levels were lower in the surfacetreated stents with respect to the untreated PU surfaces. In particular, concerning the bilaterally indwelled stents, a direct comparison between the surface properties of the stent in preventing encrustation was clearly observed. It was indeed assessed that the formation of bacterial biofilm was lower at the surface-treated catheters, whereas the precipitation of inorganic compounds were not completely inhibited. We attributed reduction of the biofilm to the presence of the surface treatments (heparin- or DLC-coatings) on the polyurethane surface. No relevant differences were found between the two surface modifications in preventing the stent encrustation upon indwelling. It was also observed that both treated and untreated PU stents did not degrade in this kind of patients.

These considerations were no more valid when the patient was a stone-former. Indeed, the recidivist calculosis induced a continuous deposition of biofilm and salts at the stent surface, thus strongly reducing the effect of the surface modification in preventing encrustation. In addition, the stents were more stiff and brittle after already one month of insertion, thus inducing patient discomfort or pain.

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It was noteworthy that both the formation of biofilm and inorganic encrustation and the success of the stent indwelling depended more significantly on the patient's pathology (i.e. stone former or not) than on the indwelling time. For these reasons, implanting a stent for a period of time longer than one month was feasible. A surface-treated polyurethane stent was also preferable with respect to the untreated PU one. However, frequent stent exchange, regardless of the surface treatment, is a general recommendation for patients suffering from a recidivist calculosis.

As a future outlook, new studies should expand in the direction of bio-degradable drugeluting polymeric stents. The preparation of such highly engineered ureteral stents should require the following properties:


We envision that such a commitment will require a strong interdisciplinary background, thus combining the fields of material science and technology to the clinical and endourological requirements.
