Microbiological investigation of an antibacterial sandwich layer system

Abstract

To allow medical application of an artificial bladder made of biocompatible polyurethane, a long-term stable antibacterial coating is required. Alone, the artificial bladder exhibits no defense against microorganisms. Silver coating provides long-term antibacterial protection by the continuous release of silver ions into aqueous solutions. To control and to prolong the rate of silver ion release, the deposited silver film has to be protected by an inert film of biocompatible polyparylene by means of chemical vapor deposition. In this study, an antibacterial artificial bladder surface was developed by the formation of a sandwich structure consisting of silver and a biocompatible polymer (polyparylene) as a diffusion barrier. Specifically, this study analyzed the correlation between polyparylene thickness and silver release to determine optimal concentrations to combat common bacteria in vitro. The release of silver from sandwich structures was investigated in vitro by testing different thicknesses of polyparylene (0, 190, 540, and 1000 nm) as a diffusion barrier. The best result was demonstrated with a thickness of 190 nm of polyparylene, which yielded a silver dispense rate of 650 pg/(cm(2)⋅min), which would yield bacteriozidal concentrations above 30 μg/l in the bladder volume. The authors confirmed the antibacterial effect in vitro against common urinary tract infection pathogens, namely, Escherichia coli and Staphylococcus cohnii. Inhibition of bacterial growth could be detected within 8 h. A diffusion assay with spherical silver spots showed concentric zones free of bacterial growth. Our results suggest the possible utility of silver-polyparylene coatings as antibacterial agents.

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

“…After 3 min of plasma exposure, the contact angle H significantly decreased from 84. 18 to 29.68 , confirming the increased hydrophilicity caused by the formation of polar oxygen-containing groups and not by the changes in roughness. Bi et al have shown by x-ray photoelectronic spectroscopy that O 2 treatment of PPX under similar exposure conditions causes the origin of two new peaks at 287.8 and 289.3 eV in the deconvoluted C 1s spectrum, which they attributed to the carbon atoms in the free carbonyl group (C¼O) and carbonate group (O 2 C¼O), respectively.…”

“…To improve adhesion of silver nanoparticles to the surface, catheters were coated with poly(p-xylylene) or parylene (PPX-N), a biocompatible polymer. 18 In a previous work, we have already optimized the silver thickness to compare PPX-N and silver particle morphology and tested minimum inhibitory concentration of silver ions in synthetic urine against E. coli and S. cohnii. 19 The aim of this study is to evaluate the antibacterial efficacy of silver/PPX catheters in a simulated body fluid (synthetic urine), including the power to prevent generation of a biofilm.…”

Bi-layer sandwich film for antibacterial catheters

“…With these measurements, it could be shown that the desired thickness of the cap layer is between 150 and 300 nm [ 40 ], which, in turn, determines the upper limit for the thickness of the silver depot. In fact, the mean value of 50 μg/L or 0.45 μmol/L corresponds exactly to the results, which are possible in an environment that is determined by the presence of Cl − , but also of urea and urease.…”

“…Among the physical and chemical standard methods to detect traces are inductively coupled plasma optical emission spectroscopy (ICP-OES), cyclic voltammetry, and atomic absorption spectroscopy (AAS). The former two methods have been extensively used and are described in [ 19 , 40 – 41 ].…”

“…After one week of additional incubation, catheters were placed again in fresh artificial urine for another three weeks. The silver concentration in all three samples was measured by ICP-OES using an ICP710-ES (Varian Medical Systems, Willich, Germany), which covers a range of typically more than five orders of magnitude [ 40 ]. This method has become standard for determining atomic concentrations in highly diluted solutions at the detection limit (5 μg/L = 50 nmol/L) [ 44 ].…”