New developments in ureteral stent design, materials and coatings

Application, Advancement, and Complication of Ureteral Stent and Encrustation: A Major Complication

Three technological aspects have a significant impact on the functioning of an optimal stent. The substance it is made up of, model or design, and coating of the surface are important areas for research. To give recognition of an ideal stent, it summarizes some essential breakthroughs that occurred. Encrustation is a regular problem that can happen when a ureteral stent is implanted in the urinary tract, and it may be dangerous. The part of the paper covers the mechanism of encrustation, stent management, and the most recent technologies created to solve this problem. Encrustation has a complicated and diverse mechanism that includes the time it stays inside, patient-specific risk factors, controlled film production, formation of biofilm, and deposition of minerals. A number of high-tech advancements in stent substances and coverings/coatings could help to reduce the danger of encrustation of stents. It's critical to determine the amount of encrustation of a stent so that therapy options can be tailored properly. For the care of ureteral stents, which are encrusted, we offer a unique therapeutic protocol. The duration of stent indwelling time has been repeatedly established to be a critical risk factor for the evolution of encrustation. The period of stent indwelling time has consistently been established to be a critical risk element for the evolution of encrustation. Patients who are predisposed to bacteriuria and urinary lithiasis are also predisposed to encrustation. Repeated urinary tract infections, diabetes, and chronic kidney failure are among the factors that might escalate urine bacterial load, which can lead to stent encrustation. Due to the prevalence of ureteral stents in urology, it's critical to keep up to date on the best ways to prevent stent encrustation, recognize high-risk patients, and remove them using multimodal techniques.

Safely increasing nephro-ureteric stent exchange intervals, resulting in significant cost savings for the interventional radiology suite, a 2-year experience in a tertiary referral centre

Aim

To evaluate the nephro-ureteric stent (NUS) insertion and exchange practice in a tertiary referral cancer centre, and determine the safety and compliance with current guidelines. We also reviewed if increasing exchange time interval from 6 to 12 weeks was safe, and if this could be adopted into our local guidelines.

Methods

A retrospective review was performed covering 24 months from January 2017 to December 2018. All NUS insertions and exchanges performed in that period were analysed, including the number of exchanges the patient underwent, the time between subsequent exchanges, and the screening time. We also reviewed the indications for stent insertion, possible causes for failed stent exchange, and factors which led to significant delays in stent exchanges for some patients. A scatterplot of screening time versus time in situ was derived and correlation analysis performed using the Pearson coefficient.

Results

Thirty-two patients underwent de novo NUS insertion during the period, and 102 NUS exchanges were performed. The interval between stent exchanges ranged from 1 to 40 weeks, with a mean of 12.3 weeks (SD = 8.96 weeks). Screening time ranged from 33 s to 17 min, with a mean of 3 min 50 s (SD = 3 min 35 s). There were 100 successful exchanges, and two failed exchanges, accounting for 1.9% of total exchanges. In both failed cases, the reason for failed exchange was due to a prolonged period between exchanges (6 months in both cases). The reason for delay for stent exchange was due to non-attendance for scheduled appointments. There was a weakly positive correlation coefficient of 0.06 (screening time versus time period between insertions); however, this was not statistically significant (p = 0.81).

Conclusion

In this retrospective review, we have demonstrated that the recommended 6-week period between stent exchanges is unnecessary in the vast majority of cases, and that a longer interval between NUS exchanges, e.g. 8–12 weeks, is safe for the patient, and reduces screening time. This reduction in procedures also provides a significant potential saving to the radiology department in both monetary expense and limited angiography suite time.

Dual-functional antibiofilm polymer composite for biodegradable medical devices

Urinary tract infections (UTI) represent one of the most common problem within the urological disorders, and it is mainly caused by biofilm formation which leads to bacterial infection. Anti-adhesion and antibacterial agents are two primary mechanisms to prevent biofilm formation; however, current strategies are insufficiently effective. In this study, we developed an effective antibiofilm biodegradable polymer with high biocompatibility. Here we embedded silver nanoparticles (AgNPs) in poly(glycerol sebacate) acrylate (PGSA) followed by superhydrophilic modification on the polymer surfaces. The modified surfaces were characterized using SEM, AFM and contact angle measurements. This anti-adhesive surface prevented the adhesion of E. coli and limited the biofilm coverage percentage to less than 3% in 24 h. In the in vitro degradation, the long-term antibiofilm performance was evaluated in Nowatzki-Stoodley artificial urine (NSAU). The surface modified AgNPs embedded PGSA (sPGSA-AgNPs) was able to effectively inhibit the formation of biofilm by reducing the biofilm coverage to less than 0.01%, and it also showed low cytotoxicity with human bladder carcinoma cell. With the effective antibiofilm, biocompatibility and biodegradability, it is possible to be applied in urological devices to ameliorate the situation of UTIs.

Double Loop Ureteral Stent Encrustation According to Indwelling Time: Results of a European Multicentric Study

Introduction: Double-J ureteral stents are subject to encrustation. Studies have shown that the encrustation onset is linked with indwelling time. In prevention, it is admitted that the Double-J stent indwelt for medium or long term should be replaced periodically. However, in the absence of guidelines, indwelling durations vary with centers' habits, stent indication, and stent materials. Our target was to evaluate the actual ureteral stent medium-/long-term indwelling times and related encrustation rates perceived by urologists in daily practice. Methods: An observational retrospective study was performed over six European centers. All data of all consecutive removed stents of the same material implanted for more than 2 months within a same 2-year referred period were collected. Three stent types of various materials, with/without coating, were evaluated. Encrustation rates were analyzed according to indwelling times and stent indication. Results: Four hundred seventy-three stents were recorded with indwelling times between 60 and 679 days. An unexpected number of long-term indwelling times were noticed: globally one-third more than 6 months, and 9% more than 1 year. In case of malignant indication, these rates were, respectively, 44% and 17%. For nonstone indication, clinically significant encrustation rates stayed extremely low before 4 months (1.3%) and quite low before 6 months (5.2%), increasing with time to reach around 10% in the long term. However, as expected, the rate was higher for stone indication with a marked increase after 4 months (8% before 4 months, nearly 17% after). Conclusion: Our data confirm a higher encrustation risk for stone patients. Long indwelling times in nonstone patients beyond 6 months or even 12 months appear to be still requested and relatively well supported in usual practice by this population.

Preparation, degradation and in vitro release of ciprofloxacin-eluting ureteral stents for potential antibacterial application

Drug-eluting stents with biodegradable polymers as reservoirs have shown great potential in the application of interventional therapy due to their capability of local drug delivery. Herein, poly(l-lactide-co-ε-caprolactone) (PLCL) with three different compositions as carriers for ciprofloxacin lactate (CIP) was coated on ureteral stents by the dipping method. To simulate a body environment, degradation behavior of PLCL as both the bulk film and the stent coating was evaluated in artificial urine (AU, pH6.20) respectively at 37°C for 120days by tracing their weight/Mn loss, water absorption and surface morphologies. Furthermore, the release profile of the eluting drug CIP on each stent exhibited a three-stage pattern, which was greatly affected by the degradation behavior of PLCL except for the burst stage. Interestingly, the degradation results on both macroscopic and molecular level indicated that the release mechanism at stage I was mainly controlled by chain scission instead of the weight loss or morphological changes of the coatings. While for stage II, the release profile was dominated by erosion resulting from the hydrolysis reaction autocatalyzed by acidic degradation residues. In addition, ciprofloxacin-loaded coatings displayed a significant bacterial resistance against E. coli and S. aureus without obvious cytotoxicity to Human foreskin fibroblasts (HFFs). Our results suggested that PLCL copolymers with tunable degradation rate as carriers for ciprofloxacin lactate could be used as a promising long-term antibacterial coating for ureteral stents.

Challenges in treatment and diagnosis of forgotten/encrusted double-J ureteral stents: the largest single-center experience

PURPOSE

We aimed to evaluate the effectiveness of the endourologic management of forgotten and/or encrusted ureteral stents together with our single-center experience.

MATERIALS AND METHODS

Fifty-four patients with forgotten double-J ureteral stents were treated in our center between January 2008 and March 2014. Encrustation and the related stone burdens were estimated by using computerized tomography and kidney-ureter-bladder radiography. The management method was chosen based on the stone burden or clinical and radiological findings.

RESULTS

Fifty-four patients, 39 males and 15 females, were included in the study. The average age of the patients was 38.2 ± 25.06 (2-86) years. The average indwelling time of the ureteral stents was 22.6 ± 30.3 (6-144) months. Six of the patients with forgotten stents had solitary kidneys. The double-J stent (DJS) was fragmented in four (7.4%) patients. A urinary system infection was present in 15 (27.7%) of the patients. The ureteral stents and related stones were successfully removed without any complications by combined endourologic techniques to achieve a stone-free state in all patients except for patient with 110 months of forgotten stent time in whom nephrectomy was performed for a nonfunctioning kidney related to the forgotten stent.

CONCLUSIONS

Forgotten/encrusted DJS may lead to complications in a range of urinary system infections, up to a loss of renal function. They can be safely and successfully removed, and the renal function can be preserved by endourologic techniques, starting with the least invasive procedures in centers highly experienced.

Intracaval Migration of Ureteral Stent

Ureteral stents have proven to be an invaluable tool for endourologists. Morbidity is minimal, but complications do exist. Up to 3 months complications are not frequent, but longer indwelling times are associated with increasing frequency of incrustation, infections, secondary stone formation, obstruction of the stented tract and migration. We report a rare case of a 33 year old pregnant patient with migration of an ureteral endoprosthesis. The patient received a right ureteral stent at 12 weeks for acute obstructive pyelonephritis. When her urologist tried to remove the ureteral stent post delivery, the stent was not found in the bladder. Ureteroscopy was performed but no ureteral stent was found. The patient showed a moderate improvement of the pyelonephritis, but complained about insidious palpitations. A CT scan was performed and showed the presence of the ureteral stent extending from the inferior vena cava up to the right atrium. Endovascular retrieval was performed through a puncture of the common femoral vein, using a curved guide that was introduced through the vena cava into the right atrium. Under fluoroscopic control, it was twisted around the stent and pulled out. The outcome was favorable, and no other complications were noted.

Prone split-leg position to manage encrusted ureteral stents in a single-stage procedure in women: Step-by-step surgical technique

The management of encrusted ureteral stents is costly, time consuming and may be risky for the patient and challenging for the urologist. Treatment modalities for encrusted stents include extracorporeal shock wave lithotripsy, cystolithopaxy, rigid or flexible ureteroscopy with intracorporeal lithotripsy, percutaneous nephrolithotomy, open surgery, and a combination of those methods. In this study we describe the management of severe forgotten encrusted ureteral stents in 3 female patients using a prone split-leg position. This position allows us to effectively treat any site and degree of stent encrustation in a single-session approach with the patient in the same position during the whole procedure. All patients were rendered stent and stone free. No complications occurred.

Ureteroarterial fistula from ureteral stump: a challenging case

Ureteroarterial fistula (UAF) is a relatively rare condition with about 150 cases reported in the literature. Since it is a potentially life-threatening condition, a prompt diagnosis and treatment are crucial. We present here a rare, challenging case of UAF diagnosed after left nephrectomy, thus involving the ureteral stump. The difficult diagnosis and treatment by contemporary use of endovascular stent placement and ureteral occlusion by mean of metallic coils and Onyx injection are discussed.

Combined endoscopic surgery in the prone-split leg position for successful single-session removal of an encrusted ureteral stent: a case report

Introduction

Although encrusted stents may lead to some unwanted complications including urinary tract obstruction, urinary sepsis, and potential loss of kidney function, there is currently no consensus on the most efficient method for managing stents that are intentionally left in situ. This is the first report describing the management of an encrusted stent using combined endoscopic surgery in the prone split-leg position in a single session.

Case presentation

A 47-year-old Asian man presented with left flank pain and macrohematuria. The patient had undergone left ureteral stenting three years previously for the treatment of left ureteral stones and hydronephrosis; however, he was lost to follow-up before the treatment for the ureter stones was completed. Therefore, the ureteral stent and stones were not removed. An abdominal radiograph and a noncontrast computed tomography scan showed encrustation along the retained stent with stone burdens in the kidney and ureter. The ureteral stent could not be removed by cystoscopy after shock wave lithotripsy of the left ureteral stones. Therefore, endoscopic lithotripsy combined with flexible ureteroscopy and miniature nephroscopy was performed with the patient in the prone split-leg position. All the stones and the encrusted ureteral stent were successfully removed in a single session.

Conclusions

In this case, percutaneous nephrolithomy in addition to flexible ureteroscopy was preferred because severe encrustation of the proximal stent and ureteral stones complicated the therapeutic strategy. Combined endoscopic techniques in the prone split-leg position can achieve successful and safe management of encrusted stents.

Renal autotransplantation for iatrogenic high-grade ureteric stricture

A 47-year-old Hispanic woman developed a chronically obstructed left kidney, due to a long-segment ureteric stricture deemed not amenable to reimplantation, following left ovarian cyst excision in 2004. Therefore, a ureteral stent requiring exchange every 3 months was necessary, due to hydronephrosis, recurrent urosepsis, chronic pain, and a poor quality of life. Her medical history was complicated by hypertension, poorly controlled diabetes mellitus, and microalbuminuria, suggesting early diabetic nephropathy. A left nephrectomy was recommended. This was deferred, due to concern for progressive kidney failure associated with her comorbidities. A radionuclide Tc-99m MAG3 renal scan revealed differential perfusion as follows: 44% left kidney and 56% right kidney, with symmetrical uptake on the renogram phase and delayed excretion on the left, which were correctted following furosemide administration. A left ureteronephrectomy with autotransplantation of the left kidney and ureteroneocystostomy was performed in 2009. Since then, the patient has experienced no further complications or need for invasive procedures, with excellent diabetic control and stable renal function (eGFR > 60 mL/min/1.73 m²). This technique is seldom employed in the surgical management of complex ureteral injuries, but may be an alternative for appropriate cases.

Encrustation of urologic double pigtail catheters-an ex vivo optical coherence tomography (OCT) study

This study aims to evaluate whether optical coherence tomography (OCT) using both the surface and the endoluminal technique is feasible to investigate the locations and degree of encrustation process in clinically used ureteral stents. After removal from patients, 14 polyurethane JJ stents were investigated. A fresh JJ served as a control. The external surfaces were examined using an endoscopic surface OCT whereas the intraluminal surfaces were investigated by an endoluminal radial OCT device. The focus was on detection of encrustation or crystalline sedimentation. In 12 female and two male patients, the median indwelling time of the ureteral catheter was 100 days (range, 19-217). Using the endoluminal OCT, the size and grade of intraluminal encrustation could be expressed as a percentage relating to the open lumen of the reference stent. The maximum encrustation observed resulted in a remaining unrestricted lumen of 15-35 % compared to the reference. The luminal reduction caused by encrustation was significantly higher at the proximal end of the ureteral stent as compared to its distal part. The extraluminal OCT investigations facilitated the characterization of extraluminal encrustation. OCT techniques were feasible and facilitated the detection of encrustation of double pigtail catheters on both the extra and intra luminal surface. Quantitative expression of the degree of intraluminal encrustation could be achieved, with the most dense and thickened occurrence of intraluminal incrustation in the upper curl of the JJ stent.

Single session removal of forgotten encrusted ureteral stents: combined endourological approach

Forgotten ureteral stents represent a difficult problem for urologists; the major complications are infection, migration, encrustation, stone formation, and multifractured stent, and a consensus on the best therapeutic approach is lacking. Here we present our experience with endoscopic management of this challenging problem and discuss the various endourological approaches for treating forgotten encrusted ureteral stents. From January 2005 to December 2010, 19 patients (11 women and 8 men) with encrusted ureteral stents were retrospectively analyzed. Combined endourologic therapies including extracorporeal shock wave lithotripsy (SWL), percutaneous nephrolithotomy (PCNL), ureterorenoscopic lithotripsy (URSL), and cystolithotripsy (CLT) were used to achieve stent removal. A total of 19 patients with encrusted ureteral stents were treated at our center. The mean patient age was 46.2 ± 18.5 years (8-81), the average indwelling time of the stent was 24.7 ± 19.0 months (8-93), and the mean hospital stay was 3.4 ± 4.0 days (range 1-15 days). Using the described combination of techniques, all stents and the associated stones were eventually removed without any complications and patients were rendered stone- and stent-free. A main element of the treatment strategy was to keep the number of interventions as low as possible. The use of various combinations of endourological techniques can achieve effective stent and stone treatment after a single anesthesia session with minimal morbidity and short hospital stay.

Predictors of morbidity in patients with indwelling ureteric stents: results of a prospective study using the validated Ureteric Stent Symptoms Questionnaire

OBJECTIVE

To assess the predictors of morbidity in patients with indwelling ureteric stents using a validated questionnaire.

PATIENTS AND METHODS

Eighty-six consecutive patients with indwelling double-J ureteric stent of different length and size enrolled at an Italian tertiary academic centre were prospectively evaluated with the Italian-validated Ureteric Stent Symptoms Questionnaire (USSQ), which explores the stent-related symptoms in six domains. Ureteric stents were placed for benign ureteric obstruction or after uncomplicated ureterorenoscopy, and were all removed after 28 days. The questionnaire was administered on days 7 and 28 after stent placement and on day 28 after removal. A plain abdominal X-ray was performed on days 7 and 28 after placement to determine stent location. Univariable and multivariable analyses tested the association of patient age, sex and body mass index (BMI), and stent side, length, calibre and distal loop location, with the index score of the various domains on days 7 and 28.

RESULTS

All patients completed the study. At multivariable analysis, on day 7, sex, BMI and stent calibre were significantly associated with one domain (general health, body pain and work performance, respectively), while location of stent distal loop was significantly associated with five domains (urinary symptoms, body pain, general health, work performanc, and sexual matters). On day 28, body mass index was significantly associated with two domains (body pain and general health), while location of stent distal loop remained significantly associated with the same five domains (urinary symptoms, body pain, general health, work performance and sexual matters).

CONCLUSION

Location of stent distal loop with respect to midline had the strongest association with most domains of the USSQ on both days 7 and 28 after stent placement. The visualization of stent distal loop crossing the midline may therefore identify patients at higher risk of post-procedural morbidity requiring early management.

Introduction to biodegradable polylactic acid ureteral stent application for treatment of ureteral war injury

OBJECTIVE

• To study the operability and effectiveness of a biodegradable ureteral stent for clinical treatment of ureteral war injury using a canine model.

MATERIALS AND METHODS

• A device was designed and employed to generate firearm fragment wounds in unilateral ureters (on randomly chosen sides) of nine beagles (Group A). The wounded ureters were then debrided and sutured. • Intravenous pyelography (IVP) and radioactive renography were performed 40, 80 and 120 days postoperatively. In Group B, firearm fragment wounds were made to the bilateral ureters in nine beagles. A polylactic acid stent was placed unilaterally (on a randomly chosen side) whereas the ureter on the other side was debrided and sutured without stenting. • Both IVP and radioactive renography were performed 40, 80 and 120 days postoperatively. The operability and effectiveness of the biodegradable ureteral stent were studied thereafter.

RESULTS

• In Group A, hydronephrosis and hydroureter occurred and worsened postoperatively on the wounded sides in all nine beagles. The ratio of the renal partial concentration indices (RPCI) between the kidneys (unwounded side : wounded side) increased. • The ratio of the kidney washout half-time between the kidneys (unwounded side : wounded side) decreased. In Group B, neither hydronephrosis nor hydroureter was found postoperatively in the stented ureters but both occurred in the unstented ureters in all nine beagles. • The ratio of RPCI between kidneys (stented side : unstented side) increased whereas the kidney washout half-time ratio between the stented and unstented sides decreased. Differences were significant.

CONCLUSION

• In Group A, the new canine model for firearm fragment wounds was tested and proved to be operable and effective. In Group B, hydronephrosis and hydroureter were effectively prevented in ureters by biodegradable stent placement compared with the non-stented ureters where hydronephrosis and hydroureter occurred. The renal concentration capacity was effectively protected and the half-time of kidney washout was shortened.

Uropathogen interaction with the surface of urological stents using different surface properties

PURPOSE

Ureteral stents commonly become infected or encrusted. Various coatings have been developed to decrease bacterial adherence. To our knowledge there has been no in vitro testing of coating with heparin to date. We determined the effects of heparin coating on bacterial adherence of common uropathogens and physical stent properties.

MATERIALS AND METHODS

Heparin coated Radiance ureteral stents (Cook) and noncoated Endo-Sof control stents were tested against triclosan eluting Triumph(R) stents and noneluting Polaris control stents for adherence of Escherichia coli, Klebsiella pneumoniae, Enterococcus faecalis, Staphylococcus aureus and Pseudomonas aeruginosa for 7 days. Adherent bacteria were determined and biofilms were visualized using fluorescent dyes. Radial, tensile and coil strength of the Radiance and Polaris stents was compared to determine the effect of heparin coating on physical stent characteristics.

RESULTS

Heparin coating did not decrease bacterial adhesion compared to its control. E. coli adhesion was limited by all stents tested. The Polaris stent showed significantly greater resistance to bacterial adherence for Klebsiella, Pseudomonas and Enterococcus than the Endo-Sof and Radiance stents but was more susceptible to S. aureus adherence. The Triumph stent resisted all bacteria except Pseudomonas and Enterococcus. Mature biofilms were observed on all stents with lower viability on the Triumph stent. Radiance stents showed higher tensile and lower compression strength than its control.

CONCLUSIONS

Heparin coating does not decrease bacterial adherence to ureteral stents. Drug eluting antimicrobials have an inhibitory effect on bacterial adherence and the Polaris stent showed the least bacterial adherence of the nondrug eluting ureteral stents tested.

Eliminating biofilm from ureteral stents: the Holy Grail

PURPOSE OF REVIEW

Biofilms continue to be a major limiting factor in the long-term use of ureteral stents, promoting the development of chronic infections and antibiotic resistance and encrustation. Apart from stent removal in conjunction with antibiotic therapy, there is currently no treatment proven successful for completely eradicating a biofilm-related infection, highlighting the need for continued research in this area.

RECENT FINDINGS

Research continues to focus mainly on biofilm prevention, specifically the development of novel coatings comprising antibacterial, antifouling or bacterial signalling compounds. Notably, all three strategies have generated candidate coatings showing recent success both in vitro and in vivo.

SUMMARY

Despite the current lack of a completely biofilm-resistant device, coating or treatment strategy, continued research into the causation of bacterial biofilm formation and the continued development of novel antibacterial, antifouling and antibiofilm compounds is promising. Future work should be aimed at more rigorous testing of candidate coatings from both physical and bacterial challenge standpoints as well as increased in-vivo investigation via clinical trials.

Biofilms in nephrology

BACKGROUND

Biofilms are bacterial communities ubiquitous to moist environments. Biofilm formation is a factor in the development and persistence of infectious diseases. In clinical nephrology, biofilms influence the development of kidney stones and affect dialysis systems, including peritoneal and central venous catheters. Biofilms also play critical roles in persistent and resistant renal and urinary tract infections.

OBJECTIVE

To describe the physiology of biofilms and potential effects of biofilms upon infectious diseases, focusing on the role of biofilms in kidney stones, indwelling catheters and dialysis equipment.

METHODS

A literature search with Medline to identify pertinent English language articles published up to early 2008 using the keywords biofilm, nephrology, renal, calculi and infection.

RESULTS/CONCLUSION

Biofilms are ubiquitous in clinical nephrology and play a role in the pathogenesis of resistant infections. Strategies for reducing the effects of biofilms in nephrology are described.

In vitro simulation of stent fracture mechanisms in ureteric nitinol wire stents

The ZebraStent is a new-concept lumen-less teflon-coated nitinol double-J wire-stent, designed to facilitate the passage of residual fragments after extracorporeal shock wave lithotripsy. In clinical practice we observed a small number of stent fractures. Hence, an experimental model was designed to simulate the physical forces that may lead to material fatigue of the stent. Flexion force was simulated by "half circular kidney mimicking structures" (HCKMS) into which the upper part of the stent was placed. All experiments were done for a minimum of 5 million cycles representing a stent indwelling time of 9 months, or until stent fracture, and simulating respiratory kidney movement. It was demonstrated that as the diameter of the HCKMS decreases, thus leading to an increased bending of the stent, the likelihood of stent fracture increased proportionally and occurred earlier. From our results it appears that stent fractures can be avoided by observing a maximum indwelling time of 6-8 weeks (which should suffice for the duration of a average SWL treatment), by choosing the correct (and shortest possible) stent length, and perhaps by manufacturer's modifications decreasing the stent's resistance to flexion. The ZebraStent concept remains appealing if it is considered as a short-term stent for post-SWL residual fragments.

Determination of urethral catheter surface lubricity

Device for in-vitro measurement of static and kinetic friction coefficient of catheter surface was developed. Tribometer was designed and constructed to work with exchangeable counter-faces (polymers, tissue) and various types of tubes, in wet conditions in order to mimic in-vivo process. Thus seven commercially available urethral catheters, made from vinyl polymers, natural latex with silicone coating, all-silicone or hydrogel coated, and one made from polyvinylchloride with polyurethane/polyvinylpyrrolidone hydrogel coating obtained in our laboratory, were tested against three various counter faces: polymethacrylate (organic glass), inner part of porcine aorta and porcine bladder mucosa. Additionally, the hydrophility/hydrophobity of tested catheters was stated via water wetting contact angle measurement. Super-hydrophilic biomaterials revealed low friction on tissue and hydrophobic counter-face; slightly hydrophobic showed higher friction in both cases, while more hydrophobic manifested low friction on tissue but high on hydrophobic polymer. The smoothest friction characteristic was achieved in all cases on tissue counter-faces. The measured values of the static coefficient of friction of catheters on bladder mucosa counter-face were as follows: the highest (0.15) for vinyl and siliconised latex catheters and 3 folds lower (0.05) for all-silicone ones. Hydrogel coated catheters exhibited the lowest static and kinetic friction factors.

[Coating with plasma-deposited functionalized diamond-like carbon to decrease encrustations on urological implants]

The double-J stents used today for palliative artificial urinary diversion very often show extreme formation of encrustations, even a short time after implantation. Despite increased scientific material development, the complication rate has not really been strongly influenced. Grant-aided by the German Federal Ministry of Education and Research, we chose a new interdisciplinary and translational approach by coating standard stent materials with plasma-deposited amorphous diamond-like carbon. These stents show clearly reduced rates of encrustation in vitro. Ongoing clinical trials demonstrate a further enhancement of this effect in vivo. The underlying mechanisms are being investigated by extending the established in vitro model, thereby pushing research in this field to a new level.

[Characteristics of encrustation of ureteric stents in patients with urinary stones]

INTRODUCTION

The goal of this prospective study was to characterize ureteral stents encrustation in stone formers.

MATERIAL AND METHODS

We report the results of a study based on 658 double-J stents (412 men and 246 women) collected from patients with in situ urinary calculi. The mean age was 48.2+/-16.0 years without differences between genders. Ureteral stent encrustation was analysed by infrared spectroscopy. Results are expressed according to the main component.

RESULTS

The mean indwelling time was 73.5+/-73.2 days. The main component in stent encrustations was calcium oxalate (43.8%), essentially the monohydrate form (27.1%), followed by proteins (27.4%), calcium phosphates (16.4% with 8.4% brushite), and uric acid (5.2%). Struvite, detected on 49 stents, was the main component in 2.4% of cases. Significant differences according to gender and age were found: calcium oxalate monohydrate, which represented 24.5% in 20 to 29 years old men class increased to 37.0% in 50 to 59 years class and then decreased in older patients. Calcium oxalate dihydrate increased with age up to 70 years in women while it felt dramatically in man beyond 50 years old. Brushite was more abundant in young men (20.4% in patients aged 20-29 years) and was decreasing beyond this age while it remained in stable proportion for all age classes in women. Increasing prevalence of uric acid encrustations with age was observed, especially in men beyond the age of 70 years. Mineral encrustations increased with the indwelling time, the part of mineral being preponderant after 15 days: 7,3% of the stents had become massively encrusted within 113 days mean period. The comparison between biomaterials showed that silicone stents were significantly less encrusted than polyurethane stents.

CONCLUSION

Stent encrustation constitutes a serious complication of ureteral stent use in stone formers. Lithogenic factors should be considered for the prevention of stent encrustation in these patients.

Advances in ureterorenoscopy

There has been a shift toward minimally invasive surgery in all surgical subspecialties in recent decades. Ureterorenoscopy represents an area in which there have been numerous advances that have resulted in excellent patient outcomes with low morbidity. Technologic advances such as miniaturization of ureteroscopes and improved video imaging have expanded the indications for ureteroscopy. The entire upper urinary tract can now be accessed for diagnosis and treatment of many common urologic conditions. Technologic research and development will continue to drive future improvements in the technique and applications for ureteroscopy.