**2.1. Experimental part: Patients, stents and characterization methods**

126 Polyurethane

Despite these recent advances, oral administration of antibiotics (e.g. ciproflaxin) cannot be avoided. Papers in this respect report that bacteria proliferation has been addressed with a local release of antibiotics or antiseptics (Cormio *et al.* 2001; John *et al.* 2007; Leung *et al.* 2001; Raad *et al.* 1997). Drug-Eluting Stent (DES) has the advantage of maximizing the local tissue levels of therapeutic agents while minimizing systemic toxicity. The problem has been faced with antibiotics incorporation (Gorman and Woolfson 2002) using novel biomimetic and bioactive silicones. For example, with a gentamicin-releasing urethral catheter, encrustation inhibition in a rabbit model has been shown in the short term (Cho *et al.* 2001). Other authors (Cadieux *et al.* 2006) reported on a triclosan-loaded ureteral stent implanted in rabbit bladders with bacterial infection. The study showed a significant decrease of urinary tract infection rate.

Another important problem with stents is that they require an additional cytoscopic procedure for their removal. Stents removal may be uncomfortable for the patient, in particular when these are encrusted, therefore requiring hospitalization and anaesthesia. Considering this big concern, the development of time bio-degradable stent materials has become a major keypoint. In principle, bio-adsorbable stents shall be designed to maintain their integrity for a given period of time, and undergo a dissolution process followed by

So far, the bio-degradable stents degrade very fast (typically 48h) or leave fragments removable by lithotripsy and ureteroscopy (Lingeman *et al.* 2003). Some tests on pigs with degradable poly-L-lactic-L-glycolic acid (PLGA) devices showed fragments embedded in the ureteral walls within cystic sacs, normally leading to fibrosis, inflammation and a large foreign body giant cell reaction (Olweny *et al.* 2002). These results show that further enhancement on their degradable characteristics is highly required. It is straightforward that the future of ureteral stents will head towards this direction, i.e. to chemically controlled biodegradation, combined to a concomitant release of biologically active molecules on target sites and with minimally invasive surgical procedures. Moreover, highly engineered stents can possibly work as a "scaffolds" for tissue regeneration via cell attachment and proliferation, finally controlling the local inflammation and healing

This chapter focuses in details on the use of PU catheters for endourological applications, providing new insights on the *in vivo* performances of PU stent. Given to our past expertise, we report on the influence of the PU surface treatments in preventing the encrustation and

As an application of PU in biomedical devices, in this paragraph we present our clinical experience with ureteral stents. In particular the focus is driven on the *in vivo* efficacy of PU stents and their surface modification with heparin or with diamond-like carbon. Parameters

the formation of bacterial biofilm when implanted into the ureter.

However, a very high control on the delivery kinetics has been not achieved yet.

spontaneous expulsion by the patient at the same time.

(Zdrahala and Zdrahala 1999).

**2. Application** 

We review here the results collected from 2006 to 2010, concerning the characterization studies on uncoated, heparin- and DLC-coated PU double-J ureteral stents (all provided by Cook Ireland LTD) after indwelling. We enrolled 59 patients (from 45 to 75 years old). 49 patients showed unilateral ureteral obstruction, thus requiring ureteral stenting in the affected ureter. The patients with unilateral obstruction received an heparin-coated, DLCcoated or an uncoated PU stent in the ureter to be treated.

10 patients suffered from bilateral obstruction, therefore the coated and uncoated PU stents were indwelled at the same time in both ureters, respectively. Each patient with bilateral obstruction received randomly both the coated stent (with heparin or with a diamond-like carbon coating) in one ureter, and the uncoated one, thus the pure PU stent, in the other ureter.

Stents indwelling was also studied for different periods of time. The stent types and indwelling times are reported in Table 1.


a None indicates that the stent surface is of pure PU.

b These stents were implanted bilaterally, thus inserting both the uncoated and the coated stents into both ureters respectively of the same patient.

**Table 1.** Stents types and indwelling periods of the PU, heparin-coated and diamond-like carbon coated PU stents.

The criteria used for patient selection for indwelling time of 1 month were mainly post– endoscopic stone treatment, ureteropelvic junction (UPJ) obstruction (awaiting surgery). In the long term indwelling (thus 3 or more months) stenting was performed in case of hydronephrosis due to extrinsic compression in patients with multi-cystic disease (no surgical indications) and UPJ obstruction after failure of endoscopic and surgical treatments (patient refused re-intervention). Pregnant women, patients with dermatitis or a burn over the insertion site were excluded. All patients enrolled in this study gave their informed consent.

Polyurethane in Urological Practice 129

IR spectroscopy was carried out directly on the inner and outer surfaces of the cut stent in Attenuated Total Reflectance (ATR) mode by means of a diamond immersion probe (as

All the described measurements were also performed on reference stents without *in-vivo*

**Figure 1.** Scheme of the analyzed surfaces for the polyurethane ureteral stents for the characterization with FESEM and IR spectroscopy IR. (a) For the plan view analysis, a cut along the stent axis was carried out for characterizing the outer (left) and inner (right) surface; (b) Cross-sections were obtained

No technical problems or violations of aseptic conditions during endoscopic procedures were recorded. In all cases retrograde uretero-pielography, performed at the start of the procedure, showed unilateral or bilateral ureteral obstruction with various degrees of

shown in Figure 1, scheme a).

by cutting the stent perpendicular to its axis.

**2.2. Clinical results** 

excretory system dilatation.

indwelling.

In all cases, double-J stents were placed using a retrograde uretero-pielography approach during cystoscopy, as suggested by the stent producer, to evaluate the excretory system.

Ciprofloxacin (500 mg twice a day) was administered for prophylaxis for the first 4 days after the procedure. Any occurrence of technical problems and violations of aseptic conditions during the procedures were recorded. The antibiotic therapy administrations, other therapeutic interventions administered during the period of indwelling, the presence of fever, infections or urinary symptoms were also recorded. After the procedure, the follow-up check included urine analysis and culture on day 15 and afterwards every three months. In addition, a complete blood count, serum creatinine levels, and ultrasonography were performed on day 30, and every 3 months thereafter. All patients received instructions to present themselves at the institution in the event of experiencing side pain, fever, dysuria, hematuria, or vomiting.

The stents were removed after different times (see Table 1) during cystoscopy. Characterization of the stents after the indwelling period was carried out using morphological and compositional analysis and the results obtained were compared with the reference stent before use. In particular they were cut both perpendicularly and parallel to the stent axis in order to obtain cross sections or plan views of the inner and outer surfaces (Figure 1). The samples were then characterized by three different techniques:


Measurements (a) and (b) were carried out at the same time. Since the stent are made of a polymeric material (polyurethane), i.e. constituted by carbon, oxygen, hydrogen, and nitrogen, these elements are excluded from the elemental analysis on the encrustation. Moreover, the specimen is fixed to the sample holder for the FESEM and EDS characterizations by a carbon sticker, the composition of which also interferes with the elemental analysis of the stent itself. For these reasons, the detection of bacterial biofilm is not possible with the EDS technique and therefore IR spectroscopy is required.

IR spectroscopy was carried out directly on the inner and outer surfaces of the cut stent in Attenuated Total Reflectance (ATR) mode by means of a diamond immersion probe (as shown in Figure 1, scheme a).

All the described measurements were also performed on reference stents without *in-vivo* indwelling.

**Figure 1.** Scheme of the analyzed surfaces for the polyurethane ureteral stents for the characterization with FESEM and IR spectroscopy IR. (a) For the plan view analysis, a cut along the stent axis was carried out for characterizing the outer (left) and inner (right) surface; (b) Cross-sections were obtained by cutting the stent perpendicular to its axis.

#### **2.2. Clinical results**

128 Polyurethane

consent.

hematuria, or vomiting.

of the samples.

and the formed encrustations;

The criteria used for patient selection for indwelling time of 1 month were mainly post– endoscopic stone treatment, ureteropelvic junction (UPJ) obstruction (awaiting surgery). In the long term indwelling (thus 3 or more months) stenting was performed in case of hydronephrosis due to extrinsic compression in patients with multi-cystic disease (no surgical indications) and UPJ obstruction after failure of endoscopic and surgical treatments (patient refused re-intervention). Pregnant women, patients with dermatitis or a burn over the insertion site were excluded. All patients enrolled in this study gave their informed

In all cases, double-J stents were placed using a retrograde uretero-pielography approach during cystoscopy, as suggested by the stent producer, to evaluate the excretory system.

Ciprofloxacin (500 mg twice a day) was administered for prophylaxis for the first 4 days after the procedure. Any occurrence of technical problems and violations of aseptic conditions during the procedures were recorded. The antibiotic therapy administrations, other therapeutic interventions administered during the period of indwelling, the presence of fever, infections or urinary symptoms were also recorded. After the procedure, the follow-up check included urine analysis and culture on day 15 and afterwards every three months. In addition, a complete blood count, serum creatinine levels, and ultrasonography were performed on day 30, and every 3 months thereafter. All patients received instructions to present themselves at the institution in the event of experiencing side pain, fever, dysuria,

The stents were removed after different times (see Table 1) during cystoscopy. Characterization of the stents after the indwelling period was carried out using morphological and compositional analysis and the results obtained were compared with the reference stent before use. In particular they were cut both perpendicularly and parallel to the stent axis in order to obtain cross sections or plan views of the inner and outer surfaces

a. FESEM (JEOL JSM 6500F) for the morphological characterization of the stent surface

b. EDS (INCA) to collect data about the chemical composition of the stent material and the

c. IR spectroscopy on Attenuated Total Reflectance mode (ATR, Bruker Equinox 55) for the identification of the chemical compounds deposited on the inner and outer surface

Measurements (a) and (b) were carried out at the same time. Since the stent are made of a polymeric material (polyurethane), i.e. constituted by carbon, oxygen, hydrogen, and nitrogen, these elements are excluded from the elemental analysis on the encrustation. Moreover, the specimen is fixed to the sample holder for the FESEM and EDS characterizations by a carbon sticker, the composition of which also interferes with the elemental analysis of the stent itself. For these reasons, the detection of bacterial biofilm is

(Figure 1). The samples were then characterized by three different techniques:

deposited encrustation at the inner and outer surface of the samples;

not possible with the EDS technique and therefore IR spectroscopy is required.

No technical problems or violations of aseptic conditions during endoscopic procedures were recorded. In all cases retrograde uretero-pielography, performed at the start of the procedure, showed unilateral or bilateral ureteral obstruction with various degrees of excretory system dilatation.

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

Polyurethane in Urological Practice 131

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

internal surface, showing the functional groups of PU, heparin and DLC.

The IR spectra of the reference-stents are shown in Figure 3 and were recorded at the

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 excretory system dilatation.
