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

Emerging medical and engineering strategies for the prevention of long-term indwelling catheter blockage

Urinary catheters have been used on an intermittent or indwelling basis for centuries, in order to relieve urinary retention and incontinence. Nevertheless, the use of urinary catheters in the clinical setting is fraught with complication, the most common of which is the development of nosocomial urinary tract infections, known as catheter-associated urinary tract infections. Infections of this nature are not only significant owing to their high incidence rate and subsequent economic burden but also to the severe medical consecutions that result. A range of techniques have been employed in recent years, utilising various technologies in attempts to counteract the perilous medical cascade following catheter blockage. This review will focus on the current advancement (within the last 10 years) in prevention of encrustation and blockage of long-term indwelling catheters both from engineering and medical perspectives, with particular emphasis on the importance of stimuli-responsive systems.

Extraction and quantification of biofilm bacteria: Method optimized for urinary catheters

Bacterial biofilms are responsible for the failure of many medical devices such as urinary catheters and are associated with many infectious and non-infectious complications. Preclinical and clinical evaluation of novel catheter coatings to prevent these infections needs to accurately quantify the bacterial load in the biofilm in vitro and ex vivo. There is currently no uniform gold standard for biofilm quantification for different surfaces and established biofilms. We have tried to establish a simple, accurate and reproducible method for extraction and measurement of biofilm bacteria on indwelling catheters, using a combination of vortexing and sonication. We demonstrate the usefulness of this method for catheters of different sizes - 3 Fr to 14 Fr - in vitro, in murine and porcine models, and indwelling in human clinical subjects. We also demonstrate consistent results with complex and polymicrobial biofilms. We believe that this standardized reproducible method will assist the assessment of biofilms in general and urological devices in particular in efforts to harness novel technologies to prevent healthcare associated infections.

Evaluation of a ureteral catheter coating by means of a BioEncrustation in vitro model

Biomaterials for applications in the urinary tract are challenged with both biofilm formation and encrustation, two highly interconnected processes. While great effort has been achieved developing promising materials there is only a limited choice of sophisticated in vitro models that are available to analyse the performance of biomaterials prior to performing delicate and expensive in vivo studies. In this study we present a complex BioEncrustation model that imitates both the processes of multi-species biofilm formation and encrustation in vitro. The resulting crystalline biofilms are compared to the deposits found on explanted ureteral stent surfaces (in vivo situation) and to deposits formed in an experimental set up that does not contain bacteria (Encrustator®). Further focus of this study is dedicated to employing the developed BioEncrustation model to evaluate the effect multifunctional coatings impose on the processes of biofilm formation and encrustation under in vitro conditions. The investigated TANP coating combines unspecific and broad band specific antibacterial properties with a degrading polymer matrix that is intended to inhibit crystal formation. The coating was prepared on both polyurethane and silicone tubes and the subsequent results of the in vitro BioEncrustation analyses reveal a promising potential for employing the coating to render ureteral stent surfaces more biocompatible.

Effect of Storage Conditions on the Long-Term Stability of Bactericidal Effects for Laser Generated Silver Nanoparticles

Silver nanoparticles (AgNPs) are widely used as antibacterial agents, but their antibacterial durability and the influence by storage conditions have not been thoroughly investigated. In this study, AgNPs were produced using a picosecond laser and stored under three different conditions: daylight, dark and cold (4 °C). The antibacterial effects of the laser AgNPs were examined against Escherichia coli in either a 14-day interval (frequent air exposure) or a 45-day interval (less frequent air exposure) using a well-diffusion method until the antibacterial effects disappeared. Results showed that the antibacterial activity of the laser generated AgNPs lasted 266 to 405 days. Frequent air exposure increased particle oxidation as measured by high-angle annular dark-field detector for scanning transmission electron microscopy (HAADF-STEM) and X-ray energy dispersive (EDX) spectroscopy, and reduced the antibacterial duration by about 13 weeks. Compared to the chemically produced AgNPs, the antibacterial effect of the laser AgNPs lasted over 100 days longer when tested in the 45-day interval, but was susceptible to oxidation when frequently exposed to the air. The laser generated AgNPs had lower antibacterial activity when stored in cold compared to that stored at room temperature. This study demonstrated the long lasting antibacterial durability of the laser generated AgNPs. Such information could help design future medical applications for the AgNPs.

A new textured polyphosphazene biomaterial with improved blood coagulation and microbial infection responses

A new poly[bis(octafluoropentoxy) phosphazene] (OFP) was synthesized for the purpose of blood contacting medical devices. OFP was further either developed into crosslinkable polyphosphazene (X-OFP) or blended with polyurethane (PU) as the mixture (OFP/PU) for improvement of mechanical property of polyphosphazene polymers. All the materials were fabricated as smooth films or further textured with submicron pillars for the assay of antimicrobial and antithrombotic properties. Results showed that crosslinkable OFP (X-OFP) and blends of OFP/PU successfully improved the mechanical strength of OFP and fewer defects of pillars were found on the textured polyphosphazene surfaces. The antithrombotic experiments showed that polyphosphazene OFP materials reduced human Factor XII activation and platelet adhesion, thereby being resistant to plasma coagulation and thrombosis. The bacterial adhesion and biofilm experiments demonstrated that OFP materials inhibited staphylococcal bacterial adhesion and biofilm formation. The surface texturing further reduced the platelet adhesion and bacterial adhesion, and inhibited biofilm formation up to 23 days. The data suggested that textured OFP materials may provide a practical approach to improve the biocompatibility of current biomaterials in the application of blood contacting medical devices with significant reduction in risk of pathogenic infection and thrombosis.

STATEMENT OF SIGNIFICANCE

The thromboembolic events and microbial infection have been the significant barriers for the long term use of biomaterials in blood-contacting medical devices. The development of new materials with multiple functions including anti-thrombosis and antibacterial surfaces is a high research priority. This study synthesized new biostable and biocompatible polyphosphazene polymers, poly[bis(octafluoropentoxy)phosphazene] (OFP) and crosslinkable OFP, and successfully improved the mechanical strength of polyphosphazenes. Polymers were fabricated into textured films with submicron pillars on the surfaces. The antimicrobial and antithrombotic assays demonstrated that new materials combined with surface physical modification have significant reduction in risk of pathogenic infection and thrombosis, and improve the biocompatibility of current biomaterials in the application of blood-contacting medical devices. It would be interest to biomaterials and bioengineering related communities.

Biomodification Strategies for the Development of Antimicrobial Urinary Catheters: Overview and Advances

Microbial burden associated with medical devices poses serious health challenges and is accountable for an increased number of deaths leading to enormous medical costs. Catheter-associated urinary tract infections are the most common hospital-acquired infections with enhanced patient morbidity. Quite often, catheter-associated bacteriuria produces apparent adverse outcomes such as urosepsis and even death. Taking this into account, the methods to modify urinary catheters to control microbial infections with relevance to clinical drug resistance are systematically evaluated in this review. Technologies to restrict biofilm formation at initial stages by using functional nanomaterials are elucidated. The conventional methodology of using single therapeutic intervention for developing an antimicrobial catheter lacks clinically meaningful benefit. Therefore, catheter modification using naturally derived antimicrobials such as essential oils, curcumin, enzymes, and antimicrobial peptides in combination with synthetic antibiotics/nanoantibiotics is likely to exert sufficient inhibitory effect on uropathogens and is extensively discussed. Futuristic efforts in this area are projected here that demand clinical studies to address areas of uncertainty to avoid development of bacterial resistance to the new generation therapy with minimum discomfort to the patients.

Anti-Adherent Biomaterials for Prevention of Catheter Biofouling

Medical device-associated infections present a leading global healthcare challenge, and effective strategies to prevent infections are urgently required. Herein, we present an innovative anti-adherent hydrogel copolymer as a candidate catheter coating with complementary hydrophobic drug-carrying and eluting capacities. The amphiphilic block copolymer, Poloxamer 188, was chemically-derivatized with methacryloyl moieties and copolymerized with the hydrogel monomer, 2-hydroxyethyl methacrylate. Performance of the synthesized copolymers was evaluated in terms of equilibrium swelling, surface water wettability, mechanical integrity, resistance to encrustation and bacterial adherence, and ability to control release of the loaded fluoroquinolone antibiotic, ofloxacin. The developed matrices were able to provide significant protection from fouling, with observed reductions of over 90% in both adherence of the common urinary pathogen Escherichia coli and encrusting crystalline deposits of calcium and magnesium salts relative to the commonly employed hydrogel, poly (hydroxyethyl methacrylate). Additionally, the release kinetics of a loaded hydrophobic drug could be readily tuned through facile manipulation of polymer composition. This combinatorial approach shows significant promise in the development of suitable systems for prevention of catheter-associated infections.

Bi-layer sandwich film for antibacterial catheters

Background: Approximately one quarter of all nosocomial infections can be attributed to the urinary tract. The infections are supposed to be mainly caused by implantations of urethral catheters and stents. A new catheter design is introduced with the aim to lower the high number of nosocomial urethral infections. In order to avoid limitations to use, the design is first applied to conventional commercially available balloon catheters. Results: The main feature of the design is a sandwich layer on both sides of the catheter wall, which is composed of a fragmented base layer of silver capped by a thin film of poly(p-xylylene). This top layer is mainly designed to release a controlled amount of Ag⁺ ions, which is bactericidal, but not toxic to humans. Simultaneously, the lifetime is prolonged to at least one year. The base layer is electrolessly deposited applying Tollens' reagens, the cap layer is deposited by using chemical vapor deposition. Conclusion: The three main problems of this process, electroless deposition of a fragmented silver film on the surface of an electrically insulating organic polymer, irreproducible evaporation during heating of the precursor, and exponential decrease of the layer thickness along the capillary, have been solved trough the application of a simple electrochemical reaction and two standard principles of physics: Papin's pot and the principle of Le Chatelier.

Transparent Copper-Loaded Chitosan/Silica Antibacterial Coatings with Long-Term Efficacy

Bacteria-contaminated inanimate surfaces within hospitals and clinics result in transmission of pathogens via direct or indirect contact, leading to increased risk of healthcare-associated infections (HAI). The use of antibacterial coatings is a potential way of reducing the bacterial burden, but many surfaces such as instrument panels and monitors necessitate the coatings to be transparent while being highly antibacterial. In this work, silica nanoparticles (SiO₂ NPs) were first grown over a layer of acrylated quaternized chitosan (AQCS) covalently immobilized on commercially available transparent poly(vinyl fluoride) (PVF) films. The SiO₂ NPs then served as nanoreservoirs for adsorption of copper ions. The coated PVF films were transparent and reduced viable bacterial count by ∼99% and 100%, when incubated with a bacteria-loaded droplet for 60 and 120 min, respectively. The killing efficacy of these coatings, after wiping 100 times, with a deionized water-wetted cloth was reduced slightly to 97-98%. The stability of these coatings can be further improved with the deposition of another layer of cationic quaternized chitosan (QCS) over the negatively charged SiO₂ NP layer, wherein the coatings maintained ∼99% killing efficacy even after 100 wipes. These coatings showed no significant toxicity to mammalian cells and, hence, can potentially be used in a clinical setting for reducing HAI.

Understanding long-term silver release from surface modified porous titanium implants

Prevention of orthopedic device related infection (ODRI) using antibiotics has met with limited amount of success and is still a big concern during post-surgery. As an alternative, use of silver as an antibiotic treatment to prevent surgical infections is being used due to the well-established antimicrobial properties of silver. However, in most cases silver is used in particulate form with wound dressings or with short-term devices such as catheters but not with load-bearing implants. We hypothesize that strongly adherent silver to load-bearing implants can offer longer term solution to infection in vivo. Keeping that in mind, the focus of this study was to understand the long term release study of silver ions for a period of minimum 6months from silver coated surface modified porous titanium implants. Implants were fabricated using a LENS™ system, a powder based additive manufacturing technique, with at least 25% volume porosity, with and without TiO2 nanotubes in phosphate buffer saline (pH 7.4) to see if the total release of silver ions is within the toxic limit for human cells. Considering the fact that infection sites may reduce the local pH, silver release was also studied in acetate buffer (pH 5.0) for a period of 4weeks. Along with that, the osseointegrative properties as well as cytotoxicity of porous titanium implants were assessed in vivo for a period of 12weeks using a rat distal femur model. In vivo results indicate that porous titanium implants with silver coating show comparable, if not better, biocompatibility and bonding at the bone-implant interface negating any concerns related to toxicity related to silver to normal cells. The current research is based on our recently patented technology, however focused on understanding longer-term silver release to mitigate infection related problems in load-bearing implants that can even arise several months after the surgery.

STATEMENT OF SIGNIFICANCE

Prevention of orthopedic device related infection using antibiotics has met with limited success and is still a big concern during post-surgery. Use of silver as an antibiotic treatment to prevent surgical infections is being explored due to the well-established antimicrobial properties of silver. However, in most cases silver is used in particulate form with wound dressings or with short-term devices such as catheters but not with load-bearing implants. We hypothesize that strongly adherent silver to load-bearing implants can offer longer-term solution towards infection in vivo. Keeping that in mind, the focus of this study was to understand the long-term release of silver ions, for a period of minimum 6months, from silver coated surface modified porous titanium implants.

Antimicrobial nitric oxide releasing surfaces based on S-nitroso-N-acetylpenicillamine impregnated polymers combined with submicron-textured surface topography

A novel dual functioning antimicrobial CarboSil 20 80A polymer material that combines physical topographical surface modification and nitric oxide (NO) release is prepared and evaluated for its efficacy in reducing bacterial adhesion in vitro. The new biomaterial is created via a soft lithography two-stage replication process to induce submicron textures on its surface, followed by solvent impregnation with the NO donor, S-nitroso-N-acetylpenicillamine (SNAP), to obtain long-term (up to 38 d) NO release. The NO releasing textured polymer surface is evaluated against four bacteria commonly known to cause infections in hospital settings and the results demonstrate that the combined strategy enables a synergistic effect on reducing the bacterial adhesion of Staphylococcus epidermidis and Pseudomonas aeruginosa bacteria.

Antimicrobial and anti-biofilm properties of polypropylene meshes coated with metal-containing DLC thin films

A promising strategy to reduce nosocomial infections related to prosthetic meshes is the prevention of microbial colonization. To this aim, prosthetic meshes coated with antimicrobial thin films are proposed. Commercial polypropylene meshes were coated with metal-containing diamond-like carbon (Me-DLC) thin films by the magnetron sputtering technique. Several dissimilar metals (silver, cobalt, indium, tungsten, tin, aluminum, chromium, zinc, manganese, tantalum, and titanium) were tested and compositional analyses of each Me-DLC were performed by Rutherford backscattering spectrometry. Antimicrobial activities of the films against five microbial species (Candida albicans, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis) were also investigated by a modified Kirby-Bauer test. Results showed that films containing silver and cobalt have inhibited the growth of all microbial species. Tungsten-DLC, tin-DLC, aluminum-DLC, zinc-DLC, manganese-DLC, and tantalum-DLC inhibited the growth of some strains, while chromium- and titanium-DLC weakly inhibited the growth of only one tested strain. In-DLC film showed no antimicrobial activity. The effects of tungsten-DLC and cobalt-DLC on Pseudomonas aeruginosa biofilm formation were also assessed. Tungsten-DLC was able to significantly reduce biofilm formation. Overall, the experimental results in the present study have shown new approaches to coating polymeric biomaterials aiming antimicrobial effect.

A review of the recent advances in antimicrobial coatings for urinary catheters

More than 75% of hospital-acquired or nosocomial urinary tract infections are initiated by urinary catheters, which are used during the treatment of 15-25% of hospitalized patients. Among other purposes, urinary catheters are primarily used for draining urine after surgeries and for urinary incontinence. During catheter-associated urinary tract infections, bacteria travel up to the bladder and cause infection. A major cause of catheter-associated urinary tract infection is attributed to the use of non-ideal materials in the fabrication of urinary catheters. Such materials allow for the colonization of microorganisms, leading to bacteriuria and infection, depending on the severity of symptoms. The ideal urinary catheter is made out of materials that are biocompatible, antimicrobial, and antifouling. Although an abundance of research has been conducted over the last forty-five years on the subject, the ideal biomaterial, especially for long-term catheterization of more than a month, has yet to be developed. The aim of this review is to highlight the recent advances (over the past 10years) in developing antimicrobial materials for urinary catheters and to outline future requirements and prospects that guide catheter materials selection and design.

STATEMENT OF SIGNIFICANCE

This review article intends to provide an expansive insight into the various antimicrobial agents currently being researched for urinary catheter coatings. According to CDC, approximately 75% of urinary tract infections are caused by urinary catheters and 15-25% of hospitalized patients undergo catheterization. In addition to these alarming statistics, the increasing cost and health related complications associated with catheter associated UTIs make the research for antimicrobial urinary catheter coatings even more pertinent. This review provides a comprehensive summary of the history, the latest progress in development of the coatings and a brief conjecture on what the future entails for each of the antimicrobial agents discussed.

Efficacy of silver/hydrophilic poly(p-xylylene) on preventing bacterial growth and biofilm formation in urinary catheters

Catheter associated urinary tract infections (CAUTI), caused by several strains of bacteria, are a common complication for catheterized patients. This may eventually lead to a blockage of the catheter due to the formation of a crystalline or amorphous biofilm. Inhibiting bacteria should result in a longer application time free of complaints. This issue has been investigated using an innovative type of silver-coated catheter with a semipermeable cap layer to prevent CAUTI. In this work, two different types of silver catheters were investigated, both of which were capped with poly(p-xylylene) (PPX-N) and exhibited different surface properties that completely changed their wetting conduct with water. The contact angle of conventionally deposited PPX-N is approximately 80°. After O₂ plasma treatment, the contact angle drops to approximately 30°. These two systems, Ag/PPX-N and Ag/PPX-N-O₂, were tested in synthetic urine at a body temperature of 37 °C. First, the optical density and the inhibition zones of both bacteria strains (Escherichia coli and Staphylococcus cohnii) were examined to confirm the antibacterial effect of these silver-coated catheters. Afterward, the efficacy of silver catheters with different treatments of biofilm formed by E. coli and S. cohnii were tested with crystal violet staining assays. To estimate the life cycles of silver/PPX-catheters, the eluted amount of silver was assessed at several time intervals by anodic stripping voltammetry. The silver catheter with hydrophilic PPX-N coating limited bacterial growth in synthetic urine and prevented biofilm formation. The authors attribute the enhanced bacteriostatic effect to increased silver ion release detected under these conditions. With this extensive preparatory analytic work, the authors studied the ability of the two different cap layers (without silver), PPX-N and oxygen plasma treated PPX-N, to control the growth of a crystalline biofilm by measuring the concentrations of the Ca²⁺ and Mg²⁺ ions after exposure of the catheters to saturated urine for 24 h. The higher concentrations of Ca²⁺ and Mg²⁺ in the precipitates on the PPX-N catheters indicates that the hydrophilic PPX-N coating is superior to the simple PPX-N coating, with regard to the formation of a crystalline biofilm. Moreover, hydrophilic PPX-N as a cap layer may promote wettability and increase silver ion release rate and thus reduce the adhesion of suspended crystals to the catheter. Reduced bacterial growth and reduced adhesion may help to prevent CAUTI.

Surface modification strategies for combating catheter-related complications: recent advances and challenges

This review summarizes the progress made in addressing bacterial colonization and other surface-related complications arising from catheter use.

One-Pot UV-Triggered o-Nitrobenzyl Dopamine Polymerization and Coating for Surface Antibacterial Application

Dopamine (DA) protected by an o-nitrobenzyl functionality on its phenolic group was synthesized as a photolabile catecholamine derivative. This compound, o-nitrobenzyl dopamine (NBDA), was more stable than DA in basic solution at pH 8.5 and will not self-polymerize when protected from light. UV irradiation of a methanolic solution of NBDA at 365 nm for 40 min induced ca. 85% deprotection. Taking advantage of the stability of NBDA, a one-pot spray coating technique for modifying surfaces with polydopamine (PDA) was developed. Using ethylene glycol with Tris buffer (pH 8.5) as the solvent for this technique, stainless steel substrates can be coated with a robust PDA layer. Silver was deposited on the PDA-coated surface after treatment with silver nitrate solution, and >80% of the deposited silver remained on the surface after 1 week immersion in water. The NBDA-Ag surface was highly effective in inhibiting Staphylococcus aureus (S. aureus) biofilm formation.

First report of macroscopic biofilm formation caused by Candida albicans on silver hydrogel-coated urinary catheters

We report macroscopic biofilms on silver hydrogel-coated urinary catheters in 2 patients from 2 different intensive care units. The catheters were removed on observation of a white, jelly layer on the catheters, respectively, 9 and 21 days after insertion. Yeast cells and pseudohyphal structures were observed with microscopy. Both isolates were identified as Candida albicans. To our knowledge, these are the first cases demonstrating the formation of macroscopic biofilm layers on silver nitrate-coated catheters in the literature.

Silver ions eluted from partially protected silver nanoparticles

The most prominent character of a new type of antibacterial urological catheters is the zebra-stripe pattern of a silver film, which is plated electroless on their interior wall and capped by a very thin semipermeable layer of parylene. This design effectively controls the release rate of Ag(+) ions in artificial urine, which has been measured as function of time with optical emission spectroscopy. By evaluating the minimum inhibitory concentration against certain strains of bacteria with solutions of AgNO3 of known concentration with the method of optical density and applying this analysis to the silver-eluting catheters, it was shown that this moderation prolongs the period of their application significantly. But to act as antibacterial agent in chlorine-containing solutions, as in urine, the presence of urea is required to avoid precipitation of AgCl and to meet or even exceed the minimum inhibitory concentration of Ag(+). The quality of the silver depot layer was further determined by the deposition rate and its morphology, which revealed that the film consisted of grains with a mean size of 150 nm.

Particulate Respirators Functionalized with Silver Nanoparticles Showed Excellent Real-Time Antimicrobial Effects against Pathogens

Particulate respirators designed to filtrate fine particulate matters usually do not possess antimicrobial functions. The current study aimed to functionalize particulate respirators with silver nanoparticles (nanosilver or AgNPs), which have excellent antimicrobial activities, utilizing a straightforward and effective method. We first enhanced the nanosilver-coating ability of nonwoven fabrics from a particulate respirator through surface modification by sodium oleate. The surfactant treatment significantly improved the fabrics' water wet preference where the static water contact angles reduced from 122° to 56°. Both macroscopic agar-plate tests and microscopic scanning electron microscope (SEM) characterization revealed that nanosilver functionalized fabrics could effectively inhibit the growth of two model bacterial strains (i.e., Staphylococcus aureus and Pseudomonas aeruginosa). The coating of silver nanoparticles would not affect the main function of particulate respirators (i.e., filtration of fine air-borne particles). Nanosilver coated particulate respirators with excellent antimicrobial activities can provide real-time protection to people in regions with severe air pollution against air-borne pathogens.

Polymeric nanobiocomposites for biomedical applications

Polymeric nanobiocomposites have recently become one of the most essential sought after materials for biomedical applications ranging from implants to the creation of gels. Their unique mechanical and biological properties provide them the ability to pass through the highly guarded defense mechanism without undergoing noticeable degradation and initiation of immune responses, which in turn makes them advantageous over the other alternatives. Aligned with the advances in tissue engineering, it is also possible to design three-dimensional extracellular matrix using these polymeric nanobiocomposites that could closely mimic the human tissues. In fact, unique polymer chemistry coupled with nanoparticles could create unique microenvironment that promotes cell growth and differentiation. In addition, the nanobiocomposites can also be devised to carry drugs efficiently to the target site without exhibiting any cytotoxicity as well as to eradicate surgical infections. In this article, an effort has been made to thoroughly review a number of different types/classes of polymeric nanocomposites currently used in biomedical fields. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1241-1259, 2017.

Biocompatible anti-microbial coatings for urinary catheters

Using a simple dip-coating mechanism, urinary catheters have been coated with poly(2-methacryloyloxyethyl)trimethylammonium chloride (pMTAC) using activator regenerated by electron transfer (ARGET)–atom transfer radical polymerization (ATRP).

Tannic acid anchored layer-by-layer covalent deposition of parasin I peptide for antifouling and antimicrobial coatings

Tannic acid and parasin I were deposited alternatively on stainless steel surface by Michael addition/Schiff base reaction-enabled layer-by-layer deposition technique.