Attenuation of encrustation by self-assembled inorganic fullerene-like nanoparticles, "Beyond the Abstract," by Racheli Ron

BERKELEY, CA (UroToday.com) - Catheter encrustation constitutes a major complication for patients who are in need of a long-term catheterization, i.e., for a period of more than one month. The complex process of encrustation has a multifactorial nature interlacing chemical, biological, and physical aspects. In brief, encrustation occurs by the precipitation of ionic salts, which are, under normal conditions, kept aqueous in the urine. The solid precipitants, or stones of encrustation, adhere to the indwelling catheter and coat it with a stony abrasive crust (see Figure 1). As time elapses, this stony crust leads to the blockage of the device and its dysfunction while indwelling in the body. Most importantly, in general, indwelling catheterization can lead to severe infection and great morbidity for the patient. An extended amount of research to counteract the problem of catheter encrustation is reported in the literature. However, currently, efforts in all frontiers have failed to eliminate it altogether.

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Figure 1: A schematic representation of urethral catheterization and the encrustation process occurring on long-term indwelling medical catheters. (a) The catheter is anchored in the bladder by an inflated balloon from which, via a tube, ends in the urethra and leads the urine out of the body. (b) The chemical reactions describing alkalization of the urine, thereby leading to precipitation of colloidal stones of encrustation in the urinal medium. (c) Deposition of the solid encrustation stones on the surfaces of the indwelling catheter is taking place. (d) With the elapsing of time, a continuous abrasive crust is formed on the catheter surfaces.

In the current research, we hypothesized that a unique nanomaterial with superior lubrication properties might attenuate attachment of the encrustation-film to the catheter surfaces. Inorganic nanoparticles of molybdenum disulfide with a fullerene-like structure (abbreviated as IF-MoS2) are spheroidal hollow closed-cage moieties, which are made of a few close MoS2 layers, similar to an onion. Their size is in the range of 50-200 nm. The IF-MoS2 nanoparticles have a low surface energy, and they exhibit very low affinity to their environment. As mentioned above, these nanoparticles are well known for their outstanding solid lubrication properties, and therefore they have already been exploited for commercial applications. Moreover, doping of these nanoparticles with a minute quantity of rhenium atoms (Re:IF-MoS2) further enhances their tribological characteristics.

The first stage of the study was dedicated to establishing a method to coat commercial all-silicone catheter specimens with the Re:IF-MoS2 nanoparticles. Scanning electron microscopy (SEM) analyses confirmed formation of a thin film of the Re:IF-MoS2 nanoparticles on the catheter surfaces. Moreover, it was demonstrated that the Re:IF-MoS2 nanoparticles were found to self-assemble on catheter surfaces in a mosaic-like tessellation (see Figure 2).

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Figure 2: SEM micrograph showing the mosaic-like tessellation of the catheter surface by the Re:IF-MoS2 nanoparticles.

In the next step, uncoated and Re:IF-MoS2-coated catheter specimens were examined under in vitro conditions for their degree of encrustation development. Both specimen types were simultaneously incubated in a model of a catheterized bladder under encrustation conditions, using artificial urine. It is a well known fact that human-urine possesses different compositions in different micturitions, even once a single donor is employed. Therefore, using artificial urine allowed testing reproducibility of the experimental results and systematic evaluation of such parameters as incubation time, enzyme concentration, etc.

A comparative investigation of both uncoated and Re:IF-MoS2-coated catheter specimens after incubation in the encrustation model demonstrated that the self-assembled Re:IF-MoS2 nanoparticles film has a significant attenuating effect on catheter encrustation. A variety of analytical tools -- including SEM, energy dispersive x-ray spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), and x-ray powder diffraction (XRD), which were applied for the assessment and quantification of the encrustation on the uncoated and Re:IF-MoS2-coated catheters -- repeatedly indicated a significant encrustation attenuation effect. While the uncoated catheters were covered by a continuous compact crust after the course of encrustation simulations, Re:IF-MoS2 nanoparticles-coated catheters exhibited only sporadically-grown stones. Furthermore, chemical analyses (EDS, XPS, XRD) of the stones showed that the Re:IF-MoS2 nanoparticles influenced neither the morphology nor the chemical composition of the in vitro encrustation stones. However, the difference in the degree of encrustation was consistently detected, regardless of the technique used for the analysis.

Although the exact mechanism for encrustation suppression on the Re:IF-MoS2-coated catheter specimens is not completely understood, a few key-characteristics of these nanoparticles might provide some fundamental guidelines. By their self-assembly into the two-dimensional, close-packed arrays, the Re:IF-MoS2 nanoparticles generated a special and totally different surface nanostructure in comparison to the bare catheter specimens. The Re:IF-MoS2 films produced a compact dense array of nano-distant bumps on the coated catheter surfaces. Therefore, it is recognized that colloidal stones approaching a catheter specimen from the urine solution and trying to deposit or to nucleate on the surface, encounter a totally different architecture from the smooth substrate of a neat catheter specimen. This nanoparticle arrangement reduces the availability of contact points for anchoring stones onto the Re:IF-MoS2-coated catheter surface, which is an established mechanism for self-cleaning surfaces. Moreover, the low surface energy of the nanoparticles and their lubrication properties come into an efficient effect and play a prominent role in the encrustation reduction.

Written by:
Racheli Ron as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.

Department of Materials and Interfaces, Weizmann Institute, Rehovot 76100, Israel

Attenuation of encrustation by self-assembled inorganic fullerene-like nanoparticles - Abstract

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