HEPARIN AS AN ANTIBACTERIAL COATING ON BIODEGRADABLE URETERAL STENTS: EXPERIMENTAL STUDY OF BRAIDSTENT®-H

INTRODUCTION

The aim of this study is to assess the effectiveness of heparin to inhibit the development of early bacteriuria as a coating for biodegradable ureteral stents.

MATERIAL AND METHODS

The BraidStent®-H biodegradable stent, whose heparin coating is incorporated by dip coating, was chosen for this study. Twenty-four swine were randomly divided into two groups: 12 animals underwent unilateral placement of the BraidStent®-H and 12 were fitted with a standard double-j stent (DJS). Bacteriuria is comparatively analyzed over time by consecutive urine sampling at 0, 1, 3, 6, 12, 24 and 48 hours. In addition, the concentration of heparin released in vitro in artificial urine at 0, 3, 6, 12, 24, 48, 72, 92 and 120 hours is determined via ELISA.

RESULTS

BraidStent®-H generates a significantly lower bacteriuria rate than a DJS at 6 and 12 hours. Heparin coating shows a significant delaying effect on the onset of bacteriuria, reaching 100% of the animals at 48 hours, compared to the DJS, which takes place at 6 hours. ELISA results reveal the presence of heparin in urine for a total of 72 hours. The coating does not affect the degradation of the device, which is completed at 6 weeks.

CONCLUSIONS

Heparin evidences an effective inhibition of early bacteriuria, showing its potential as an antibacterial coating for biodegradable ureteral stents. Future studies should focus on the development of long-term heparin coatings for biodegradable materials.

EVALUATION OF THE RELEASE RATE OF A CHEMOTHERAPEUTIC AGENT INCORPORATED AS A COATING ON A BIODEGRADABLE URETERAL STENT. IN VITRO STUDY

INTRODUCTION

To assess the release rate of Mitomycin C (MMC) after its adherence to a biodegradable ureteral stent (BraidStent™-MMC) by dip coating in order to evaluate its potential application as an adjuvant treatment for upper tract urothelial carcinoma.

MATERIAL AND METHODS

The dip coating technique is applied to a total of 10 fragments of the BraidStent™ catheter which has a polymeric matrix as a coating. Each 3 cm fragment is immersed 10 times in pure MMC crystallising in methanol and finally obtaining the formation of microlayers on its surface. After drying, each fraction of the stent is immersed in 5 ml of artificial urine to study its interaction with this medium. The samples remain in an orbital shaker at 36ºC and the medium is exchanged under sterile conditions after 12, 24, 48, 48, 72, 96 and 120h. At each replacement, the remaining urine is analysed by HPLC-DAD to quantify the presence of the cytotoxic agent.   

RESULTS

During the first 12h, MMC is completely released reaching a mean concentration of 52.22 mg/L. Comparing this result with those previously obtained with the first BraidStent ™ -MMC formulation (10.82mg/L), it is determined that this technique allows to increase the release rate up to 5 times.

CONCLUSIONS

The release rate of Mitomycin C from a biodegradable ureteral stent is increased by integrating a polymeric matrix with microlayers in its coating. Further trials are needed to achieve the therapeutic dose for clinical application in oncology patients.

[Usefulness of renal resistive index in the diagnosis and evolution of the obstructive uropathy. Experimental study]

OBJECTIVE

The study was focused on determining the effectiveness and reliability of using the renal resistance index as a method of diagnosing and monitoring the evolution of obstructive uropathy treatment. For this purpose, we conducted an experimental study on a homogenous group of animals that all had the same level of obstruction.

MATERIAL AND METHODS

15 healthy female pigs were used. The experiment was divided into three phases: phase I consisted of a study prior to unilateral pyeloureteral junction obstruction, performing retrograde ureteropyelography, renal B-mode ultrasound and duplex-Doppler (of both kidneys) at a level of the arcuate arteries. Then, the obstruction was performed on the animals. Phase II commenced by diagnosing the lesion, 6 weeks after the previous phase, by means of the aforementioned diagnostic methods. Finally, the endourological treatment was completed. Animals were monitored (Phase III) 15 weeks after the endopyelotomy, using the same methods as in the study, by assessing the urinary tract (fluoroscopy) and both kidneys by determining the renal resistance index and ratio.

RESULTS

All the animals in the study showed signs of urinary obstruction on radiology and renal ultrasound 6 weeks after ureteral ligature. After treatment and follow-up, all animals showed signs of having recovered from the obstructive uropathy. Values of deltaRI during the 3 phases are detailed below. Fase I deltaIR = 0.01, Fase II deltaIR = 0.11, Fase III deltaIR = 0.02.

CONCLUSION

RI determination using duplex-Doppler is effective for distinguishing obstructive dilatation using non-invasive techniques. However, this parameter provides very slight differences and it can also be influenced by too many direct and indirect factors (observational, patient age, anaesthesia, haemodynamic parameters, etc.), to supplant the classic diagnostic methods.

Modelos experimentales en la cirugía laparoscópica urológica

We present the experience of the Minimally Invasive Surgery Centre (MISC) in the development of a modular training model in laparoscopic surgery. The experience analysis includes the description of the training objectives, the learning process of simple and advance laparoscopic urologic techniques, as well as some current and future considerations before applying the laparoscopic techniques. This learning program pretends to optimize the knowledge of the surgeon and the clinical practice of these surgical techniques. The phases of the learning process have been classified in four levels, which include different modules and models and whose application will depend on the experience and surgical skills. This pyramidal training system permits the student to advance step by step through each level depending on her surgical skills. We have presented our experience in twelve courses about laparoscopic urology and four courses of laparoscopic radical prostatectomy, in which more than 300 urologists have assisted. Furthermore, some Spanish Urology Units have been developing special experimental training programs on laparoscopic radical prostatectomy, partial nephrectomy or laparoscopic dismembered pyeloplasty with Anderson-Hynes technique. It has been previously described that laparoscopic modular learning constitutes a very useful concept to avoid problems related to an incomplete and incorrect learning process. Also it seems clear that the laparoscopic training reduces the learning curve in laparoscopic urologic techniques.

[Endourologic treatment of ureteral strictures. Experimental comparative study]

OBJECTIVES

To compare efficacy and efficiency of two different endourological therapies for ureteral stricture, and to evaluate pathological reactions of the ureters following both endourological techniques.

MATERIAL AND METHODS

Ten pigs underwent experimental induction of ureteral stricture. Four weeks later, ureteral strictures were demonstrated by imaging techniques. Animals were divided in two groups, according to the received therapy: -Group I. (5 pigs), endoballoon rupture endoureterotomy. -Group II (5 pigs), Acucise balloon endoureterotomy. Ureteral stents were placed for 3 weeks following endoureterotomy. Animals were followed up four weeks after ureteral stents retrieval.

RESULTS

In all cases, ureteral stricture was proved four weeks after model induction. In one case from each group, it was needed a second balloon dilatation to achieve complete endoureterotomy. Leading to ureteral restenosis, stent migration occurred in one animal from group I. Success was achieved in 80% of cases from group I, and 100% of cases from group II.

CONCLUSIONS

Our results suggest that both endourological therapies are effective. Nevertheless, a higher efficiency was proved with Acucise endoureterotomy. Our pathological evidences do not support Davis's studies on ureteral healing following endoureterotomy.

[Diagnosis and follow up with endoluminal ultrasound in the endourologic treatment of experimental ureteral stenosis]

OBJECTIVES

The objective of this study is to determine the utility and reliability of endoluminal sonography transducer in the diagnosis and follow up after the treatment of partial ureteral obstruction.

MATERIAL AND METHODS

Ten healthy Large White female pigs, weighing 35-40 Kg, were induced a partial ureteral obstruction by laparoscopic approach. All the studied animals underwent the same three-phase procedure; inducement (phase 1), diagnosis (phase 2) and treatment of experimental strictures (phase 3), as well as, a month follow up. In all the stages of the study endoluminal sonography was used to diagnose the stricture and to assess the treatment, as well as, to measure the internal ureter diameter.

RESULTS

The endoluminal ultrasonography was able to assess, in all the cases, the affectation of all the ureteral layers. All the animals develop a ureteral stricture after a four weeks ligature and, except in one animal, they progress favourably after the treatment using the balloon rupture technique of the stricture ureter. The means of the ureteral diameter are: phase 1 (0.46 +/- 0.10 cm), phase 2 (0.30 +/- 0.17 cm), phase 3 (0.47 +/- 0.13 cm).

CONCLUSIONS

The use of the IVUS in the diagnosis of ureteral strictures results safe and useful, as well as, its application in the election and in the assessment of the treatment.