Eliminating biofilm from ureteral stents: the Holy Grail

Electrosprayed zein nanoparticles as antibacterial and anti-thrombotic coatings for ureteral stents

Ureteral stents are among the most frequently used human implants, with urothelium trauma, blood clots, and bacterial colonization being their main reasons for failure. In this study, berberine-loaded zein (ZB) nanoparticles with high drug encapsulation efficiency (>90 %) were fabricated via electrospray on flat and 3D stainless steel structures. Physico-chemical characterization revealed that the ZB nanoparticles created a highly hydrophilic, antioxidant, and scratch-resistant continuous coating over the metal structure. Results showed that the drug release rate was faster at neutral pH (i.e., PBS pH 7.4) than in an artificial urine medium (pH 5.3) due to the different swelling behavior of the zein polymeric matrix. In vitro evaluation of ZB particles onto human dermal fibroblasts and blood cells demonstrated good cell proliferation and enhanced anti-thrombotic properties compared to bare stainless steel. The ability of the electrosprayed zein particles to resist bacterial adherence and proliferation was evaluated with Gram-negative (Escherichia coli) bacteria, showing high inhibition rates (-29 % and -46 % for empty and berberine-loaded particles, respectively) compared to the medical-grade metal substrates. Overall, the proposed composite coating fulfilled the requirements for ureteral applications, and can advance the development of innovative biocompatible, biodegradable, and antibacterial coatings for drug-eluting stents.

Influence of biofilms on morbidity associated with short-term indwelling ureteral stents: a prospective observational study

PURPOSE

To evaluate the influence of biofilms on morbidity associated with short-term ureteral stenting using contemporary methods of biofilm examination and validated assessment of symptoms.

METHODS

Patients undergoing temporary ureteral stenting for secondary ureterorenoscopy due to urinary calculi were prospectively included. The German Ureteral Stent Symptoms Questionnaire (USSQ) was used to assess stent-associated morbidity. Biofilms were removed from stents using 'pinhole extraction', a novel, validated, abrasion-based technique. Extracted biofilms were analyzed for total mass, bacterial load and mineral components. Correlation between total biofilm mass and USSQ total score was the primary outcome variable analyzed using Spearman correlation. Secondary outcomes included correlations between various biofilm characteristics and symptoms.

RESULTS

94 patients were included in the analysis. Extracted biofilm mass had a median of 37.0 mg (0-310.2 mg) per stent. No correlation between total biofilm mass and USSQ total score was found (Spearman r = 0.012; p = 0.911). Correlations between biofilm characteristics and morbidity were generally weak and not significant. Significant correlations could be found between biofilm mass and hematuria (r = 0.280; p = 0.007), and between the number of bacteria (qPCR) and the USSQ subscore for pain (r = 0.243; p = 0.019) and the intake of analgesics (r = 0.259; p = 0.012).

CONCLUSION

Based on elaborated biofilm examination methods and validated self-reported outcome measures, our findings indicate that biofilms might aggravate some lower urinary tract symptoms but are not the main trigger for stent-associated morbidity in short-term ureteral stenting.

Advances in ureteral stents

Ureteral stents are commonly used in urology. Every urologist is familiar with the problems that are associated with stents including infection, encrustation, and bothersome symptoms. These problems limit and affect the use of ureteral stents which are necessary, even in light of the problems they can cause. New designs such as a helically cut ureteral stent which is designed to stretch and conform to the ureter is designed to improve comfort. Drug-eluting designs with an antimicrobial (triclosan) are designed to reduce bacterial adherence to ureteral stents. Chlorhexidine, an antiseptic, has been incorporated into a stent and held in place by a slow release varnish to prevent biofilm formation. Combinations of antibiotics coated directly on the stent and administered systemically have been shown to reduce stent colonization both in vitro and in vivo. Gel-based ureteral stents were also showed to reduce bacterial infection and colonization. Bioabsorbable materials have also been designed to reduce infection, symptoms and prevent the forgotten stent syndrome. Newer designs including stents based on guidewire technology, gels, and a combination of self-expanding wire stents with polymer films are reviewed. There is hope on the horizon that new stents will be able to effectively tackle problems that are often seen with ureteral stents.

Silver in medicine: a brief history BC 335 to present

Silver is a naturally occurring element. Similar to other metals, the ionized form of silver (Ag(+1)) has known antimicrobial properties. A number of wound dressings incorporating silver ion or silver compounds have recently been developed and marketed. In addition, the antimicrobial effects of silver are currently being promoted in consumer products such as clothing and household appliances. The present use of silver in medical and consumer products has prompted concerns for potential toxicity and ecological effects, including induction of microbial resistance to antibiotics. These concerns ignore the fact that silver has been used for medicinal purposes for several thousand years. A historical review of the uses of silver in medicine is presented.

Antifouling coating with controllable and sustained silver release for long-term inhibition of infection and encrustation in urinary catheters

Urinary tract infections constitute a large proportion of nosocomial infections, and the urinary catheter is the most important predisposing factor. Encrustation induced by urease-producing uropathogens like Proteus mirabilis causes further complications. In the present work, a strategy for controllable and sustained release of silver over several weeks has been developed for combating bacterial infection and encrustation in urinary devices. Silver nanoparticles (AgNPs) were first immobilized on polydopamine (PDA) pre-treated silicone catheter surface and this was followed by another PDA coating. The number of AgNP-PDA bilayers could be manipulated to control the amount of silver loaded and its subsequent release. Poly(sulfobetaine methacrylate-co-acrylamide) was then grafted to provide an antifouling outer layer, and to ensure free diffusion of Ag from the surface. The micron-scale combination of an antifouling coating with AgNP-PDA bilayers reduced colonization of the urinary catheter by uropathogens by approximately two orders of magnitude. With one and two AgNP-PDA bilayers, the coated catheter could resist encrustation for 12 and 45 days, respectively, compared with approximately 6 days with the Dover™ silver-coated catheter. Such anti-infective and anti-encrustation catheters can potentially have a large impact on reducing patient morbidity and healthcare expenditure.

Prevention of initial biofilm formation on ureteral stents using a sustained releasing varnish containing chlorhexidine: in vitro study

BACKGROUND AND PURPOSE

Ureteral stents are being used exceedingly in the field of urology, and with advancements in endourology, this trend is increasing. Bacterial colonization and proliferation on the stent surface may result in urinary tract infections (UTIs) necessitating the administration of antibiotics that, in turn, may lead to the development of antibiotic-resistant bacterial strains. Several studies have shown that sustained release varnish (SRV) combined with antibiotics or antiseptics can prevent the proliferation of bacteria on urethral catheters. This is the first study that evaluates this technique implemented on ureteral stents.

MATERIALS AND METHODS

We evaluated growth inhibition on ureteral stent segments coated with chlorhexidine (CHX) 1% SRV. The tests were conducted using common urinary pathogens: Enterococci, Pseudomonas, and Escherichia coli. Coated stent segments were inserted into bacterial suspensions. Controls included uncoated stent segments and stents coated with placebo SRV (without CHX).

RESULTS

Bacterial growth measured as turbidity and as colony-forming units showed a significant inhibition effect of initial bacteria adhesion to the CHX-SRV coated stent segments compared with the controls (P<0.001). This inhibitory effect was apparent in each of the bacteria tested and was confirmed by inspection of the stent segments under an electron microscope. In a kinetic experiment using CHX 2% SRV, we were able to prolong the growth inhibition effect from 1 week to nearly 2 weeks.

CONCLUSIONS

We believe this technique may play a significant role in reducing ureteral stent-associated UTIs. Further studies are needed before this approach can be implemented in clinical practice.

Does heparin coating reduce encrustation of biliary plastic endoprostheses? A prospective randomized trial

OBJECTIVE

Common bile duct stenting is widely performed for bridging benign and malignant obstructions. A major limitation is early stent occlusion making regular stent exchange necessary. Covalent binding of glycosaminoglycanes to polyethylene stents proved to reduce encrustation in urological implants. Since development of urological and biliary stent occlusion shows parallels, the aim of the study was to evaluate the efficacy of heparin coating of biliary endoprostheses in preventing encrustation.

MATERIAL AND METHODS

In a prospective randomized trial, heparin-coated and native stents were endoscopically placed for almost 90 days on average. After removal, all stents were dried (50°C, 24 h), weighed and after longitudinal incision visible encrustation and discoloration recorded. Fifty-three patients (21 females/32 males, 70 ± 12 (42-87) years) were included; 13 patients (4 females/9 males, 58-79 years) completed the study according to the protocol.

RESULTS

After removal, mean weight of encrustation in native stents was more than double as high as of covered stents (native: 37.9 ± 19.8 (16-93) mg; covered: 17.6 ± 6.7 (9-33) mg). In 12 of 13 cases, the encrustation weight of the native stent was higher than that of the corresponding covered stent in the same patient. Premature stent explantation became necessary in 3 of 13 native stents, because of recurrent jaundice or cholangitis but only in 1 of 13 covered stents. After longitudinal incision, the three uncovered stents showed excessive encrustation whereas no significant encrustation was found in the covered prosthesis. Altogether, covered stents showed less visible accumulation of clogging material and discoloration than native stents.

CONCLUSIONS

Covalent bound heparin is highly effective in preventing encrustation of biliary polyethylene endoprostheses.

Antibacterial performance of polydopamine-modified polymer surfaces containing passive and active components

A growing number of device-related nosocomial infections, elevated hospitalization costs, and patient morbidity necessitate the development of novel antibacterial strategies for clinical devices. We have previously demonstrated a simple, aqueous polydopamine dip-coating method to functionalize surfaces for a wide variety of uses. Here, we extend this strategy with the goal of imparting antifouling and antimicrobial properties to substrates, exploiting the ability of polydopamine to immobilize polymers and induce metal nanoparticle formation. Polydopamine was deposited as a thin adherent film of 4 nm thickness from alkaline aqueous solution onto polycarbonate substrates, followed by grafting of antifouling polymer polyethylene glycol and in situ deposition of silver nanoparticles onto the polydopamine coated polycarbonate substrates. Elemental and morphological surface analyses confirmed successful grafting of polyethylene glycol brushes onto polydopamine-coated substrates, as well as spontaneous silver nanoparticle formation for polydopamine-coated substrates incubated in silver-nitrate solutions. Sustained silver release was observed over at least 7 days from silver-coated substrates, and the release kinetics could be modulated via additional polydopamine overlayers. In vitro functional assays employing gram negative and positive strains demonstrated dual fouling resistance and antibacterial properties of the coatings due to the fouling resistance of grafted polyethylene glycol and antibacterial effect of silver, respectively. Polycarbonate substrates coated only with silver using a method similar to existing commercial coatings provided an antibacterial effect but failed to inhibit bacterial attachment. Taking into account the previously demonstrated substrate versatility of polydopamine coatings, our findings suggest that this strategy could be implemented on a variety of substrate materials to simultaneously improve antifouling and antimicrobial performance.

Comparative efficacy of commercially available and emerging antimicrobial urinary catheters against bacteriuria caused by E. coli in vitro

OBJECTIVES

To compare the efficacy of both commercially available and emerging urinary catheter technologies in relation to their effects on bacteriuria caused by Escherichia coli in vitro. Antiseptic urinary catheters have recently become commercially available and others are in the developmental stage.

METHODS

Silver alloy-coated catheters, antibiotic Nitrofurazone (NF)-coated catheters, and nitric oxide (NO)-coated catheters were tested against a noncoated control for their antiseptic ability. Inhibition of bacterial growth, biofilm formation, and the number of live bacteria within the biofilm, using up to 10(3) bacterial load were evaluated. Experiments were performed either in E. coli containing Luria broth media or in urine infected with E. coli.

RESULTS

NF- and NO-coated catheters had equivalent antimicrobial activity and eradicated all bacteria in planktonic and biofilm states. Silver-coated catheters had no effect on E. coli growth or biofilm formation compared with the control, although silver-coated catheters did inhibit bacterial levels within the biofilm by 50%.

CONCLUSIONS

NF- and NO-coated catheters are highly effective in preventing planktonic growth and biofilm formation. Silver-coated catheters were not found to be effective in this study.

Evaluation of madurahydroxylactone as a slow release antibacterial implant coating

Madurahydroxylactone (MHL), a secondary metabolite with antibacterial activity was evaluated for its suitability to generate controlled drug release coatings on medical implant materials. A smooth and firmly attached layer could be produced from a precursor solution on various metallic implant materials. In physiological salt solutions these coatings dissolved within a time period up to one week. A combination of MHL with a broad spectrum fluoroquinolone antibiotic was used to create a coating that was active against all bacterial strains tested. The time period during which the coating remained active against Pseudomonas aeruginosa was investigated. The results indicated a delayed drug release from single layer coatings in the course of seven days. MHL was biocompatible in cell culture assays and could after a delay even serve as a cell adhesion substrate for human or murine cells. The findings indicate a potential for MHL for the generation of delayed release antimicrobial implant coatings.

[Urinary tract infections and Urolithiasis]

The classic "infection stone" struvite is formed as a result of metabolic activity of urease-positive bacteria from alkaline urine with pH-values above 7.5. Due to improved infection diagnostics and antibiotic therapy, the occurrence of infection-related urinary stones in the western industrialized world decreases, despite the generally increasing prevalence rates of urolithiasis in these societies. Struvite is often associated with other mineral phases. These accessory mineral phases could indicate other, non-infection-related causes of urinary stone formation. Thus, mineral analysis is always recommended. Struvite stones as well as struvite encrustations on urinary tract implants are characterized by rapid growth. The rapid growth-related embedding of urease-positive bacteria in the crystalline material makes the urinary stone a persistent source of recurrent urinary tract infections. According to the German Society of Urology guidelines on urolithiasis, a patient with the diagnosis "infection stone" should be assigned to the "high-risk" patient group. Complete stone and debris removal, as well as a special metaphylaxis strategy are required to initiate successful stone therapy.

Electrical microcurrent to prevent conditioning film and bacterial adhesion to urological stents

Long-term catheters remain a significant clinical problem in urology due to the high rate of bacterial colonization, infection, and encrustation. Minutes after insertion of a catheter, depositions of host urinary components onto the catheter surface form a conditioning film actively supporting the bacterial adhesion process. We investigated the possibility of reducing or avoiding the buildup of these naturally forming conditioning films and of preventing bacterial adhesion by applying different current densities to platinum electrodes as a possible catheter coating material. In this model we employed a defined environment using artificial urine and Proteus mirabilis. The film formation and desorption was analyzed by highly mass sensitive quartz crystal microbalance and surface sensitive atomic force microscopy. Further, we performed bacterial staining to assess adherence, growth, and survival on the electrodes with different current densities. By applying alternating microcurrent densities on platinum electrodes, we could produce a self regenerative surface which actively removed the conditioning film and significantly reduced bacterial adherence, growth, and survival. The results of this study could easily be adapted to a catheter design for clinical use.