**2.3. Characterization results on starting stents surfaces**

The starting stent surfaces were analyzed prior to indwelling, in order to evaluate the differences between the pure PU surface, the heparin- and DLC-coatings.

To understand the performances of both coatings in preventing bacterial adhesion and encrustation with respect to the PU material, the stents were also characterized after different indwelling times (see Table 1 for details). These results will be discussed in the next paragraphs.

Here we report on the results from the different characterization techniques concerning the stents before patient's indwelling (hereafter "reference-stents"). It is intended that all the results and comments presented in the Paragraph 2.4 are based on the comparison with these reference stents.

Figure 2 shows the surface morphology (measured by FESEM) of the PU (uncoated), heparin-coated and DLC-coated stents. The internal and external surfaces of the PU stent (Figure 2.a and 2.b) presented several irregularities, attributed to the polyurethane particles (of about 0,5 – 1 μm) or undispersed barium sulfate particles, used to impart radiopacity to the stent. The elemental analysis by means of EDS showed no additional results, since carbon, oxygen and nitrogen are excluded due to the reasons mentioned in the Paragraph 2.1. For this reason the results of the EDS analysis are not shown.

At the edge of heparin-coated reference-stent it was possible to observe the smooth heparin layer on the polyurethane substrate (Figure 2.d), with a thickness of about 5 μm.

The EDS shows the presence of sulphur, an element present in the heparin chemical formula together with C, O and N. Barium was present in the black paint line, used as fluoroscopic marker, at the outer surface of the catheter.

Figure 2.e shows the external surface, close to a lateral drainage hole, of the DLC-coated reference-stent. At the internal surface of this stent (Figure 2.f) several grains and thin cracks were observed, possibly attributed to the carbon coating. The elemental analysis on DLCcoated stent surface detected carbon, oxygen and nitrogen, attributed to PU.

excretory system dilatation.

next paragraphs.

these reference stents.

None of the patients reported fever, side pain or voiding symptoms during the period of study. Urine culture was negative in all cases. In three patients, groups frequency/urgency symptoms were recorded. Until stents removal, these patients were successfully treated with antimuscarinics. Follow-up examination revealed no diferences in blood count, serum creatinine and ultrasonographic features of kidney and ureter with respect to the baseline

Stents were removed without technical difficulties in all cases. No technical problems occurred during the endoscopic procedures on ten patients showing chronic unilateral obstruction. In these cases, uretero-pielography showed ureteral obstruction with severe

The starting stent surfaces were analyzed prior to indwelling, in order to evaluate the

To understand the performances of both coatings in preventing bacterial adhesion and encrustation with respect to the PU material, the stents were also characterized after different indwelling times (see Table 1 for details). These results will be discussed in the

Here we report on the results from the different characterization techniques concerning the stents before patient's indwelling (hereafter "reference-stents"). It is intended that all the results and comments presented in the Paragraph 2.4 are based on the comparison with

Figure 2 shows the surface morphology (measured by FESEM) of the PU (uncoated), heparin-coated and DLC-coated stents. The internal and external surfaces of the PU stent (Figure 2.a and 2.b) presented several irregularities, attributed to the polyurethane particles (of about 0,5 – 1 μm) or undispersed barium sulfate particles, used to impart radiopacity to the stent. The elemental analysis by means of EDS showed no additional results, since carbon, oxygen and nitrogen are excluded due to the reasons mentioned in the Paragraph

At the edge of heparin-coated reference-stent it was possible to observe the smooth heparin

The EDS shows the presence of sulphur, an element present in the heparin chemical formula together with C, O and N. Barium was present in the black paint line, used as fluoroscopic

Figure 2.e shows the external surface, close to a lateral drainage hole, of the DLC-coated reference-stent. At the internal surface of this stent (Figure 2.f) several grains and thin cracks were observed, possibly attributed to the carbon coating. The elemental analysis on DLC-

layer on the polyurethane substrate (Figure 2.d), with a thickness of about 5 μm.

coated stent surface detected carbon, oxygen and nitrogen, attributed to PU.

values. During indwelling, all the stents were well tolerated.

**2.3. Characterization results on starting stents surfaces** 

2.1. For this reason the results of the EDS analysis are not shown.

marker, at the outer surface of the catheter.

differences between the pure PU surface, the heparin- and DLC-coatings.

**Figure 2.** FESEM results of the stents surfaces of PU, Heparin-coated PU and carbon-coated PU.

The IR spectra of the reference-stents are shown in Figure 3 and were recorded at the internal surface, showing the functional groups of PU, heparin and DLC.

Polyurethane in Urological Practice 133

The spectrum of the heparin-coated PU surface (in red) shows some new features with respect to the PU reference-stent (in black). In particular, the broad band from 3700 to 3100 cm-1, representing water and –OH groups, showed a lower intensity. A similar decrease was observed for the bending peak of water at 1690 cm-1. It was than concluded that the heparin coated stent surface showed lower hydration than the uncoated one. In contrast, stretching peaks at 3300 cm-1, belonging to –NH groups, and peaks at 2900 and 2860 cm-1, representing alkyl –CH2 and –CH3 groups, increased, since both functional groups were also present in the heparin chemical formula. For the same reason, similar changes in intensity were detected at 1400 cm-1 for the peak related to –CH2 and –CH3 bending vibrations. Additional peaks appeared in the range from 1650 to 1600 cm-1, due to the presence of carboxylate (-COOH) and sulphate (-SO4) groups belonging to heparin. The other peaks of the red

In the following sections, the results on the indwelled stents are reported and divided according to the indwelling time (from 1 to 3 months, more than 3 months) and the adopted approach (unilateral or bilateral indwelling). In addition, some example will be given in order to show how the patient pathology, such as recidivist calculosis, would affect the stent surface.

In this section we will examine the surface characterization of stents indwelled unilaterally

The samples were analyzed by means of the three techniques described above. The characterization aimed to evaluate the presence of bacterial biofilm and inorganic encrustations, such as calcium oxalate (CaC2O4), sodium chloride (NaCl), brushite (CaHPO4∙2H2O) and other salts, such as silica (SiO2) and compounds of magnesium (Mg) and potassium (K). The obtained data were used to evaluate the behavior of PU ureteral

Figure 4 shows the comparison between the surfaces of PU, heparin-coated and DLC-coated stents, indwelled unilaterally into three different patients. They were all indwelled into the patient's ureter after the stone removal from the kidney by endoscopic lithotripsy with holmium laser. In the cases of both heparin-coated and DLC-coated stents almost clean and encrustation-free surfaces were observed (Figures 4.e-4.l). In contrast, higher levels of encrustation were detected at both the inner and outer surfaces of the PU stent (Figures 4.a-4.d). The elements found at both inner and outer stent surfaces by means of Energy Dispersive Spectroscopy (EDS) are reported in Table 2. Some inorganic salts were detected at all the stent surfaces, such as sodium chloride (NaCl, evidenced by the presence of both Na and Cl, Table

and for a period ranging from 1 to 3 months. We have examined (see also Table 1):

stent *in vivo* according to the indwelling time and the surface treatment.

spectrum are no longer discussed, since they belonged to the PU substrate.

**2.4. Characterization results on the indwelled stents** 

*2.4.1. Stents indwelled unilaterally for 1 - 3 months* 

i. 19 PU stents;

ii. 14 heparin-coated stents; iii. 4 DLC-coated stents.

**Figure 3.** IR of the stents surface: comparison between PU stents without coating and with heparin and diamond-like carbon coatings.

The PU spectrum (in black) in the 3800-1200 cm-1 region reflected the vibration modes of its functional groups. Hydroxyl groups (-OH) and physisorbed hydration water were responsible for the bands from 3700 to 3100 cm-1. The stretching vibration of the –NH group was associated to the band at 3300 cm-1, while peaks at 2900 and 2860 cm-1 are the stretching vibrations of alkyl –CH2 and –CH3 groups. The peak at 1690 cm-1 represents another vibration mode (bending) of clustered water. The band at 1740 cm-1 indicated the carboxyl group C=O vibration mode, at 1450 cm-1 the mode of the aromatic ring (C6H6) and at 1400 cm-1 the bending modes of alkyl –CH2 and –CH3 groups. In the spectral zone below 1200 cm-1 only collective vibrations of the single bonds were observed since the bands in this range are typical of the polymer chain and constitute its "fingerprint".

In the DLC-coated stent spectrum (in blue), no significant differences were appreciable with respect to the previous PU spectrum, however several changes in the peak intensities were observed. In particular, the band from 3400 to 3250 cm-1, representing water, –OH groups and amine group (-NH) were more intense. A similar increase was observed for to the bending peak of water at 1690 cm-1, concluding that the DLC-coated stent surface was more hydrophilic than the untreated polyurethane catheter. Stretching peaks at 2940 and 2850 cm-1, representing alkyl –CH2 and –CH3 groups, also showed an increased intensity, due to the plasma treatment implanting hydrocarbon ions. For the same reason, similar changes in intensity were observed at 1400 cm-1 for the peak related to –CH2 and –CH3 bending vibrations and an additional peak at 1597 cm-1 attributed to the C=C group. The IR light beam penetrated under the thin DLC-modified surface and also detected the polyurethane surface. For example, the aromatic ring belonging to PU was also slightly observed in the range between 1430 and 1290 cm-1.

The spectrum of the heparin-coated PU surface (in red) shows some new features with respect to the PU reference-stent (in black). In particular, the broad band from 3700 to 3100 cm-1, representing water and –OH groups, showed a lower intensity. A similar decrease was observed for the bending peak of water at 1690 cm-1. It was than concluded that the heparin coated stent surface showed lower hydration than the uncoated one. In contrast, stretching peaks at 3300 cm-1, belonging to –NH groups, and peaks at 2900 and 2860 cm-1, representing alkyl –CH2 and –CH3 groups, increased, since both functional groups were also present in the heparin chemical formula. For the same reason, similar changes in intensity were detected at 1400 cm-1 for the peak related to –CH2 and –CH3 bending vibrations. Additional peaks appeared in the range from 1650 to 1600 cm-1, due to the presence of carboxylate (-COOH) and sulphate (-SO4) groups belonging to heparin. The other peaks of the red spectrum are no longer discussed, since they belonged to the PU substrate.

#### **2.4. Characterization results on the indwelled stents**

In the following sections, the results on the indwelled stents are reported and divided according to the indwelling time (from 1 to 3 months, more than 3 months) and the adopted approach (unilateral or bilateral indwelling). In addition, some example will be given in order to show how the patient pathology, such as recidivist calculosis, would affect the stent surface.

#### *2.4.1. Stents indwelled unilaterally for 1 - 3 months*

In this section we will examine the surface characterization of stents indwelled unilaterally and for a period ranging from 1 to 3 months. We have examined (see also Table 1):

i. 19 PU stents;

132 Polyurethane

diamond-like carbon coatings.

range between 1430 and 1290 cm-1.

**Figure 3.** IR of the stents surface: comparison between PU stents without coating and with heparin and

The PU spectrum (in black) in the 3800-1200 cm-1 region reflected the vibration modes of its functional groups. Hydroxyl groups (-OH) and physisorbed hydration water were responsible for the bands from 3700 to 3100 cm-1. The stretching vibration of the –NH group was associated to the band at 3300 cm-1, while peaks at 2900 and 2860 cm-1 are the stretching vibrations of alkyl –CH2 and –CH3 groups. The peak at 1690 cm-1 represents another vibration mode (bending) of clustered water. The band at 1740 cm-1 indicated the carboxyl group C=O vibration mode, at 1450 cm-1 the mode of the aromatic ring (C6H6) and at 1400 cm-1 the bending modes of alkyl –CH2 and –CH3 groups. In the spectral zone below 1200 cm-1 only collective vibrations of the single bonds were observed since the bands in this range

In the DLC-coated stent spectrum (in blue), no significant differences were appreciable with respect to the previous PU spectrum, however several changes in the peak intensities were observed. In particular, the band from 3400 to 3250 cm-1, representing water, –OH groups and amine group (-NH) were more intense. A similar increase was observed for to the bending peak of water at 1690 cm-1, concluding that the DLC-coated stent surface was more hydrophilic than the untreated polyurethane catheter. Stretching peaks at 2940 and 2850 cm-1, representing alkyl –CH2 and –CH3 groups, also showed an increased intensity, due to the plasma treatment implanting hydrocarbon ions. For the same reason, similar changes in intensity were observed at 1400 cm-1 for the peak related to –CH2 and –CH3 bending vibrations and an additional peak at 1597 cm-1 attributed to the C=C group. The IR light beam penetrated under the thin DLC-modified surface and also detected the polyurethane surface. For example, the aromatic ring belonging to PU was also slightly observed in the

are typical of the polymer chain and constitute its "fingerprint".


The samples were analyzed by means of the three techniques described above. The characterization aimed to evaluate the presence of bacterial biofilm and inorganic encrustations, such as calcium oxalate (CaC2O4), sodium chloride (NaCl), brushite (CaHPO4∙2H2O) and other salts, such as silica (SiO2) and compounds of magnesium (Mg) and potassium (K). The obtained data were used to evaluate the behavior of PU ureteral stent *in vivo* according to the indwelling time and the surface treatment.

Figure 4 shows the comparison between the surfaces of PU, heparin-coated and DLC-coated stents, indwelled unilaterally into three different patients. They were all indwelled into the patient's ureter after the stone removal from the kidney by endoscopic lithotripsy with holmium laser. In the cases of both heparin-coated and DLC-coated stents almost clean and encrustation-free surfaces were observed (Figures 4.e-4.l). In contrast, higher levels of encrustation were detected at both the inner and outer surfaces of the PU stent (Figures 4.a-4.d).

The elements found at both inner and outer stent surfaces by means of Energy Dispersive Spectroscopy (EDS) are reported in Table 2. Some inorganic salts were detected at all the stent surfaces, such as sodium chloride (NaCl, evidenced by the presence of both Na and Cl, Table

2). In addition, oxides of calcium (evidenced only from the presence of Ca, whereas oxygen and carbon were both not taken into account by EDS analysis), silica (revealed by Si element), phosphorous (P) and potassium (K) were collected. In the case of the heparin-coated stent, the sulphur (S) element present at both inner and outer surfaces clearly derived from the heparin layer.

Polyurethane in Urological Practice 135

**% Element Atom**

<sup>0</sup> Cl K 88.78

**%** 

**PU stent Heparin-coated stent DLC-coated stent Inner Surface Outer Surface Inner Surface Outer Surface Inner Surface Outer Surface** 

Na K 29.17 Na K 37.71 Na K 22.79 Na K 0.00 Na K 0.00 Na K 10.70 Mg K 0.00 Mg K 0.00 Mg K 0.00 Mg K 0.00 Mg K 0.00 Mg K 0.00 Si K 3.55 Si K 0.00 Si K 0.00 Si K 0.00 Si K 0.00 Si K 0.62 P K 2.14 P K 2.48 P K 0.00 P K 0.00 P K 0.00 P K 0.00 S K 1.89 S K 0.00 S K 38.40 S K 61.01 S K 0.00 S K 0.00

K K 2.46 K K 2.06 K K 0.00 K K 0.00 K K 0.00 K K 0.00 Ca K 34.99 Ca K 0.00 Ca K 2.61 Ca K 0.00 Ca K 0.00 Ca K 0.00 Bi K 5.35 Bi K 19.66 Ba L 26.13 Ba L 38.99 Ba L 0.00 Ba L 0.00

IR spectroscopy (here only the spectra carried out at the internal surfaces are shown, see Figure 5) confirmed the previous findings (a higher content of water was observed in the case of DLC-coated stent, blue spectrum). It was therefore concluded that the stent surfaces

By combining the results of the three characterization techniques, the following considerations can be drawn: (i) the inner surface of the stents, independently from the surface treatment, was more encrusted than the outer one; (ii) the PU stent showed higher

level of inorganic encrustation with respect to both surface-modified stents.

**Table 2.** EDS analysis on PU, heparin-coated and DLC-coated stent surfaces after 1-3 months of

**% Element Atom**

**% Element Atom**

**% Element Atom**

Cl K 20.45 Cl K 38.09 Cl K 10.07 Cl K 0.00 Cl K 100.0

**Element Atom**

unilateral indwelling.

**% Element Atom**

were clean and the bacterial biofilm was not detected.

**Figure 5.** IR of the internal stent surfaces.

**Figure 4.** FESEM results of PU, heparin-coated and DLC-coated polyurethane stents surfaces after unilateral indwelling for a period ranging from 1 to 3 months.


**Table 2.** EDS analysis on PU, heparin-coated and DLC-coated stent surfaces after 1-3 months of unilateral indwelling.

IR spectroscopy (here only the spectra carried out at the internal surfaces are shown, see Figure 5) confirmed the previous findings (a higher content of water was observed in the case of DLC-coated stent, blue spectrum). It was therefore concluded that the stent surfaces were clean and the bacterial biofilm was not detected.

**Figure 5.** IR of the internal stent surfaces.

134 Polyurethane

heparin layer.

2). In addition, oxides of calcium (evidenced only from the presence of Ca, whereas oxygen and carbon were both not taken into account by EDS analysis), silica (revealed by Si element), phosphorous (P) and potassium (K) were collected. In the case of the heparin-coated stent, the sulphur (S) element present at both inner and outer surfaces clearly derived from the

**Figure 4.** FESEM results of PU, heparin-coated and DLC-coated polyurethane stents surfaces after

unilateral indwelling for a period ranging from 1 to 3 months.

By combining the results of the three characterization techniques, the following considerations can be drawn: (i) the inner surface of the stents, independently from the surface treatment, was more encrusted than the outer one; (ii) the PU stent showed higher level of inorganic encrustation with respect to both surface-modified stents.

To see how the patient's pathology and conditions affected the ureteral stents, in Figure 6 we compare the surfaces of three PU, heparin-coated and DLC-coated stents respectively, indwelled into stone-former patients. All the catheter surfaces were heavily encrusted; however lower level of depositions were observed at both the coated stent surfaces (Figures 6.d-6.i) with respect to the PU stent (Figures 6.a-6.c).

Polyurethane in Urological Practice 137

The encrustation of the three stents was mainly composed of calcium oxalate, as clearly detected by the IR spectroscopy (Figure 7) and the EDS analysis (here not shown). In particular, IR spectrum of the oxalate crystals was very well defined, with the characteristic peaks at 1706 and 1313 cm-1 representing the vibration modes of C=O and C-O groups, respectively. These spectra showed the high purity of the isolated bio-mineral on the stent surfaces. In addition, the vibration modes of the polymeric substrate (heparin, DLC and polyurethane) were no longer recognizable. One can then conclude that the encrustation was thicker than the depth of the analysis (about 1 μm using the Attenuated Total Reflection

These findings do not allow to conclude which stent is more or less encrusted with respect to the surface treatment. Indeed, in stone former patients with recidivist calculosis, whatever stent is applied, the urologist has to plan frequent stent exchange (the suggested indwelling

**Figure 7.** IR spectra of the three stents surfaces, also depicted in Figure 6, clearly showing the vibration

In this paragraph we present the results obtained from the surface characterization of both heparin-coated and unmodified PU stents, indwelled longer than three months. This indwelling time actually exceed the recommendation of the stent producer, and the results are therefore quite interesting. All these patients refused the stent substitution after 3 months, thus the stents were substituted or definitely removed once the consent of patient was given. Again, the stent study has to be divided according to the patient's pathology,

*2.4.2. Stents unilaterally indwelled longer than 3 months* 

time by the producer is one month indeed), due to the ease of stent encrustation.

(ATR) detection mode).

modes of calcium oxalate.

that is, stone-former patient or not.

**Figure 6.** FESEM images of PU, heparin-coated and DLC-coated stents after indwelling of 1-3 months into stone-forming patients.

The encrustation of the three stents was mainly composed of calcium oxalate, as clearly detected by the IR spectroscopy (Figure 7) and the EDS analysis (here not shown). In particular, IR spectrum of the oxalate crystals was very well defined, with the characteristic peaks at 1706 and 1313 cm-1 representing the vibration modes of C=O and C-O groups, respectively. These spectra showed the high purity of the isolated bio-mineral on the stent surfaces. In addition, the vibration modes of the polymeric substrate (heparin, DLC and polyurethane) were no longer recognizable. One can then conclude that the encrustation was thicker than the depth of the analysis (about 1 μm using the Attenuated Total Reflection (ATR) detection mode).

136 Polyurethane

To see how the patient's pathology and conditions affected the ureteral stents, in Figure 6 we compare the surfaces of three PU, heparin-coated and DLC-coated stents respectively, indwelled into stone-former patients. All the catheter surfaces were heavily encrusted; however lower level of depositions were observed at both the coated stent surfaces (Figures

**Figure 6.** FESEM images of PU, heparin-coated and DLC-coated stents after indwelling of 1-3 months

into stone-forming patients.

6.d-6.i) with respect to the PU stent (Figures 6.a-6.c).

These findings do not allow to conclude which stent is more or less encrusted with respect to the surface treatment. Indeed, in stone former patients with recidivist calculosis, whatever stent is applied, the urologist has to plan frequent stent exchange (the suggested indwelling time by the producer is one month indeed), due to the ease of stent encrustation.

**Figure 7.** IR spectra of the three stents surfaces, also depicted in Figure 6, clearly showing the vibration modes of calcium oxalate.

#### *2.4.2. Stents unilaterally indwelled longer than 3 months*

In this paragraph we present the results obtained from the surface characterization of both heparin-coated and unmodified PU stents, indwelled longer than three months. This indwelling time actually exceed the recommendation of the stent producer, and the results are therefore quite interesting. All these patients refused the stent substitution after 3 months, thus the stents were substituted or definitely removed once the consent of patient was given. Again, the stent study has to be divided according to the patient's pathology, that is, stone-former patient or not.

The first example shows the comparison between PU and heparin-coated stents indwelled unilaterally into non-stone former patients after calculus removal by lithotripsy.

Polyurethane in Urological Practice 139

In contrast to the previous results, the heparin-coated stent showed higher degree of encrustations at both inner and outer surfaces with respect to the PU stent (Figure 9.a, b, c). In particular, needle-like crystals were observed a higher magnification at the internal stent surface (Figure 9.e and f). This morphology corresponded to the calcium oxalate crystals, and was confirmed by both EDS spectroscopy (due to the presence of calcium in high percentages in Table 3), and IR spectroscopy (Figure 10.b). Indeed both spectra collected at

the inner and outer surfaces indicated a thick layer of pure calcium oxalate.

**Figure 9.** FESEM images of PU and heparin-coated stents indwelled unilaterally for more than 3

In this example no general conclusion can be drawn concerning the comparison of the two stents, since the surface-modified stent and PU one were indwelled into two different

months in stone former patients.

patients, although both stone-formers.

Despite the long indwelling time and the producer recommendation, both stents were quite free from encrustation (Figure 8 shows FESEM characterization). The encrustation thickness was measured 2.5 μm at the PU stent, whereas it was not enough compact to form a layer on the heparin-coated surfaces. The results obtained by EDS and IR spectroscopy confirmed the absence of bacterial biofilm on both stent surfaces. In addition, the PU surface showed a higher percentage of sodium chloride and silica with respect to the heparin-coated one. From these findings, one can conclude that the encrustation levels of the surface-treated stent were lower than the PU one.

**Figure 8.** Surface morphology of PU and heparin-coated stents inserted unilaterally for more than 3 months.

The second example referred to the stents indwelled into stone-former patients for longterm periods (more than 3 months).

In contrast to the previous results, the heparin-coated stent showed higher degree of encrustations at both inner and outer surfaces with respect to the PU stent (Figure 9.a, b, c). In particular, needle-like crystals were observed a higher magnification at the internal stent surface (Figure 9.e and f). This morphology corresponded to the calcium oxalate crystals, and was confirmed by both EDS spectroscopy (due to the presence of calcium in high percentages in Table 3), and IR spectroscopy (Figure 10.b). Indeed both spectra collected at the inner and outer surfaces indicated a thick layer of pure calcium oxalate.

138 Polyurethane

months.

term periods (more than 3 months).

stent were lower than the PU one.

The first example shows the comparison between PU and heparin-coated stents indwelled

Despite the long indwelling time and the producer recommendation, both stents were quite free from encrustation (Figure 8 shows FESEM characterization). The encrustation thickness was measured 2.5 μm at the PU stent, whereas it was not enough compact to form a layer on the heparin-coated surfaces. The results obtained by EDS and IR spectroscopy confirmed the absence of bacterial biofilm on both stent surfaces. In addition, the PU surface showed a higher percentage of sodium chloride and silica with respect to the heparin-coated one. From these findings, one can conclude that the encrustation levels of the surface-treated

**Figure 8.** Surface morphology of PU and heparin-coated stents inserted unilaterally for more than 3

The second example referred to the stents indwelled into stone-former patients for long-

unilaterally into non-stone former patients after calculus removal by lithotripsy.

**Figure 9.** FESEM images of PU and heparin-coated stents indwelled unilaterally for more than 3 months in stone former patients.

In this example no general conclusion can be drawn concerning the comparison of the two stents, since the surface-modified stent and PU one were indwelled into two different patients, although both stone-formers.


Polyurethane in Urological Practice 141

spectroscopic characterizations (not shown here) revealed phosphorous, potassium and sodium chloride salts at both stents surfaces, with higher percentages of bacterial biofilm at

**Figure 11.** The surface morphology of PU and heparin-coated stents indwelled bilaterally into the same

In the second case, we examined the stents after bilateral indwelling into a patient presenting a recidivist calculosis into both her kidneys. In particular the patient had multiple lithiasis (3 calculus) at the lower calyx of the left kidney. Stenting into both the ureters was carried out after removal of stones by endoscopic lithotripsy with holmium laser; however residual lithiasis was still present. The DLC-treated stent was positioned into the left ureter, to verify its performance after calculus removal. The PU stent was indwelled at the same time into the right ureter. After one month both stents were removed, due to patient low tolerance. This patient underwent two repetitive stents indwelling, always

having pain and very low tolerance towards every catheter.

the inner surface of the PU stent.

patient for one month.

**Table 3.** Results of the EDS analysis carried out at both the inner and outer surfaces of PU and heparincoated stents after prolonged unilateral indwelling into stone-former patients.

**Figure 10.** IR spectroscopy of the internal and external surfaces of (a) PU stent and (b) heparin-coated stent, unilaterally indwelled into stone-former patient for a period longer than 3 months.

#### *2.4.3. Stents bilaterally indwelled for 1 month*

The bilateral indwelling is the ideal condition to compare the effectiveness of the surface treatment in preventing encrustation, since both stents are exposed to the same patient's conditions.

Here we report on two examples of surface-modified and PU stents, bilaterally indwelled for one month into a non-stone former patient and, in a second case, into a stone-former one.

In the first example, shown in Figure 11 by FESEM, heparin-coated and PU untreated stents were indwelled bilaterally after calculus removal by lithotripsy with holmium laser. Both the treated and untreated surfaces showed low levels of encrustation. The EDS and IR spectroscopic characterizations (not shown here) revealed phosphorous, potassium and sodium chloride salts at both stents surfaces, with higher percentages of bacterial biofilm at the inner surface of the PU stent.

140 Polyurethane

**PU stent Heparin-coated stent Inner Surface Outer Surface Inner Surface Outer Surface Element Atom% Element Atom% Element Atom% Element Atom%**  Na K 34.75 Na K 0.00 Na K 10.14 Na K 0.00 Mg K 0.00 Mg K 0.00 Mg K 0.00 Mg K 0.00 Si K 18.65 Si K 37.77 Si K 0.00 Si K 0.00 S K 4.39 S K 0.00 P K 0.00 P K 2.56 Cl K 32.53 Cl K 37.93 S K 24.46 S K 0.00 K K 0.00 K K 0.00 Cl K 3.42 Cl K 0.00 Ca K 0.00 Ca K 0.00 K K 0.00 K K 0.00 Br L 0.00 Br L 0.00 Ca K 43.82 Ca K 97.44 Bi M 9.69 Bi M 0.00 Ba L 18.17 Ba L 0.00 **Table 3.** Results of the EDS analysis carried out at both the inner and outer surfaces of PU and heparin-

coated stents after prolonged unilateral indwelling into stone-former patients.

**Figure 10.** IR spectroscopy of the internal and external surfaces of (a) PU stent and (b) heparin-coated

The bilateral indwelling is the ideal condition to compare the effectiveness of the surface treatment in preventing encrustation, since both stents are exposed to the same patient's

Here we report on two examples of surface-modified and PU stents, bilaterally indwelled for one month into a non-stone former patient and, in a second case, into a stone-former one. In the first example, shown in Figure 11 by FESEM, heparin-coated and PU untreated stents were indwelled bilaterally after calculus removal by lithotripsy with holmium laser. Both the treated and untreated surfaces showed low levels of encrustation. The EDS and IR

stent, unilaterally indwelled into stone-former patient for a period longer than 3 months.

*2.4.3. Stents bilaterally indwelled for 1 month* 

conditions.

**Figure 11.** The surface morphology of PU and heparin-coated stents indwelled bilaterally into the same patient for one month.

In the second case, we examined the stents after bilateral indwelling into a patient presenting a recidivist calculosis into both her kidneys. In particular the patient had multiple lithiasis (3 calculus) at the lower calyx of the left kidney. Stenting into both the ureters was carried out after removal of stones by endoscopic lithotripsy with holmium laser; however residual lithiasis was still present. The DLC-treated stent was positioned into the left ureter, to verify its performance after calculus removal. The PU stent was indwelled at the same time into the right ureter. After one month both stents were removed, due to patient low tolerance. This patient underwent two repetitive stents indwelling, always having pain and very low tolerance towards every catheter.

Figure 12 shows the high degree of encrustation, in particular concerning the PU stent. In particular, the encrustation was thicker than 40 μm and was composed of bacterial biofilm and inorganic salts, such as brushite (CaHPO4·2H2O ) and sodium chloride.

Polyurethane in Urological Practice 143

**2.5. Results summary** 

43% of brushite).

**3. Conclusion** 

2. bacterial biofilm;

Summarizing the results obtained upon stent indwelling into 59 patients, some statistical considerations can be drawn. Considering only the surface-treated stents, the level of bacterial biofilm stabilized after three months of indwelling (incidence of the encrustation on the total amount of heparin-coated stents analyzed: 81.3%), remaining almost constant for longer indwelling time (78.6%). The incidence of sodium chloride, silica and salts of magnesium and potassium increased with the indwelling time or due to the recidivist calculosis of the patient. Interestingly, the highest levels of calcium oxalate and brushite were found at the surface-modified stents indwelled for 3 months into stone-former patients (75% for both compounds). For indwelling times longer than 3 months, the levels of calcium

oxalate and brushite decreased (42.9 % for calcium oxalate and 57.1% for brushite).

Concerning the PU stents, high contents of sodium chloride and other salts were generally observed in high percentages (up to 100%), despite the indwelling time and the patient pathology. The highest percentages of both bacterial biofilm and calcium oxalate were observed after already 3 months of indwelling time (85% of biofilm , 50% of calcium oxalate,

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

1. inorganic compounds, like calcium oxalate, sodium chloride, brushite and salts of

We have divided the obtained data according to their indwelling time, the unilateral or

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

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

bilateral indwelling and the patient's tendency to form calculus (stone-former or not).

Spectroscopy were used to characterize both inner and outer catheter surfaces. With these techniques two kinds of deposits were detected at the stent surfaces:

potassium, magnesium and phosphorous;

and untreated PU stents did not degrade in this kind of patients.

In contrast, the encrustation level of the DLC-coated stent was not so compact and uniform as in the untreated PU stent. It was therefore assumed that the presence of the DLC surface modification prevented partially the encrustation deposition and the bacterial adhesion, despite the pathology of the patient. In particular the DLC-coating seemed to guarantee the stent lumen free for urine drainage (Figure 12.c).

From EDS analysis, no particular inorganic compounds were identified on the surface of the DLC-coated stent (data not shown).

For the overall 20 stents indwelled bilaterally for one month (see Table 1) it was concluded that both surface treatments effectively prevented or at least decreased the levels of encrustation by both bacterial biofilm and inorganic compounds, with respect to the pure PU catheter. It was found that the highest incidence of encrustations took place at the inner surface of the catheter.

**Figure 12.** FESEM images of PU and DLC-coated ureteral stents indwelled bilaterally for one month into the same patient, suffering from recidivist calculosis.

#### **2.5. Results summary**

142 Polyurethane

Figure 12 shows the high degree of encrustation, in particular concerning the PU stent. In particular, the encrustation was thicker than 40 μm and was composed of bacterial biofilm

In contrast, the encrustation level of the DLC-coated stent was not so compact and uniform as in the untreated PU stent. It was therefore assumed that the presence of the DLC surface modification prevented partially the encrustation deposition and the bacterial adhesion, despite the pathology of the patient. In particular the DLC-coating seemed to guarantee the

From EDS analysis, no particular inorganic compounds were identified on the surface of the

For the overall 20 stents indwelled bilaterally for one month (see Table 1) it was concluded that both surface treatments effectively prevented or at least decreased the levels of encrustation by both bacterial biofilm and inorganic compounds, with respect to the pure PU catheter. It was found that the highest incidence of encrustations took place at the inner

**Figure 12.** FESEM images of PU and DLC-coated ureteral stents indwelled bilaterally for one month

into the same patient, suffering from recidivist calculosis.

and inorganic salts, such as brushite (CaHPO4·2H2O ) and sodium chloride.

stent lumen free for urine drainage (Figure 12.c).

DLC-coated stent (data not shown).

surface of the catheter.

Summarizing the results obtained upon stent indwelling into 59 patients, some statistical considerations can be drawn. Considering only the surface-treated stents, the level of bacterial biofilm stabilized after three months of indwelling (incidence of the encrustation on the total amount of heparin-coated stents analyzed: 81.3%), remaining almost constant for longer indwelling time (78.6%). The incidence of sodium chloride, silica and salts of magnesium and potassium increased with the indwelling time or due to the recidivist calculosis of the patient. Interestingly, the highest levels of calcium oxalate and brushite were found at the surface-modified stents indwelled for 3 months into stone-former patients (75% for both compounds). For indwelling times longer than 3 months, the levels of calcium oxalate and brushite decreased (42.9 % for calcium oxalate and 57.1% for brushite).

Concerning the PU stents, high contents of sodium chloride and other salts were generally observed in high percentages (up to 100%), despite the indwelling time and the patient pathology. The highest percentages of both bacterial biofilm and calcium oxalate were observed after already 3 months of indwelling time (85% of biofilm , 50% of calcium oxalate, 43% of brushite).
