The Erlanger silver catheter was developed in order to reduce the risk of infection from long-term catheters by means of silver ions, which are known to have antibacterial properties. This is achieved by incorporating silver into polyurethane catheters by means of a special procedure. The aim of this materials science study was to verify the release of silver ions from the polyurethanes. Static experiments were carried out following the usual norms. Clinically relevant dynamic experiments, which were designed and constructed at this institute, were also performed. The eluates from both experiments were analyzed by anodic stripping voltammetry. Polyurethanes filled with silver, as used in the Erlanger silver catheter, release silver in static as well as in dynamic experiments. If the experimentally determined releases are converted to the usual catheter length of 30 cm, the release is about 0.1 microgram/l. This lies in the order of concentrations that have been reported in the literature to be antibacterial.

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Joyce-Wöhrmann et. al/Thermoplastic Silver-Filled Polyurethanes for Antimicrobial Catheters shown for a hydrogen-and for an oxygen-plasma pretreated sample. Both samples show corrosion similar to filiform corrosion, but the morphology of the corrosive attack is different.The hydrogen-plasma treated sample shows a significant delamination around the defect. In the delaminated area only a thick corrosion layer can be found, the a-SIC:H-film is completely gone. This is not surprising since definitely active corrosion has occurred beneath the film and the volume of the iron oxides, which are the main corrosion products, is very large. If the adhesion of the layer to the substrate is not very high, the layer will separate from the substrate due to the high mechanical stress. [2] The corrosion filaments that are characteristic of filiform corrosion are not very pronounced in this case, but can be seen in outlines at the edges of the corroded area.The oxygen-treated sample shows a more typical filiform behavior, such as on coated aluminum. [3] Very thin filaments grow in different directions, a closer view is shown in Figure 3. In the head of the filament a different color can be seen. This is typical of filiform corrosion. This is the active head, where the corrosion reactions take place. ESCA measurements in this active head show a huge amount of chloride, which is characteristic of a filiform attack. The area behind the head is filled with corrosion products. Typically, in the case of organic coated samples the coatings stay intact, but in the case investigated the layer breaks into pieces and falls off the sample, because this inorganic film is too brittle. In contrast to the hydrogen-plasma treated sample the oxygen treated sample shows a much better adhesion of the layer to the substrate, so the area around the defect is not completely delaminated.The pretreatment of steel substrates with oxygen or hydrogen plasmas shows a significant difference in the corrosion properties. It could be shown that a-SiC:H layers are able to protect the steel substrate from atmospheric attack. In particular, they are very effective in preventing water from diffusing to the interface. At very high humidity (near 100 %) no corrosion could be observed for exposure times up to weeks. At 85 % very fast filiform corrosion occurs. The reason for this drastic change in corrosion stability with the comparatively small change in humidity is the object of current research. The adhesion of the a-SiC:H-coating to the iron oxide obtained with the oxygen plasma is better than for the surface reduced in the hydrogen plasma, as can be seen from the different degree of loss in coating around the filiform filaments. ExperimentalSamples of a common non-alloyed steel (St37) were used as substrate. The steel substrates were ground and polished to a mirror finish. The diameter of the round samples was 15 mm. Before insertion in the plasma chamber they were cleaned in 2-propanol in an ultrasonic bath and rinsed with distilled water. The deposition was ca...

Despite a very high level of hygiene in clinics, catheter-associated infections are still considered a critical source of complications in medicine. The "Erlanger Silberkatheter", based on polyurethanes filled with silver was designed to decrease the number of adhering bacteria on inner and outer catheter surfaces. It was shown that the mechanical properties of the thermoplastic polyurethanes (TPU) are not negatively influenced by silver particles and the manufacturing process. As silver ions are known to be an effective antimicrobial agent, the rate of silver ions released from the catheter material was measured using anodic stripping voltammetry. Polyurethanes filled with silver release silver ions in concentrations which show an antimicrobial effect according to literature. In vitro and in vivo tests have demonstrated the antimicrobial efficacy of the material developed. The risk of a critical catheter-associated infection after a five day implantation could be reduced by 70 %. First catheters based on this antimicrobial material are on the market. IntroductionCatheters have been used in increasing numbers during recent years. Their use, however, has been accompanied by a substantial proportion of catheter-related infections. The rate of foreign-body-related infections due to centralvenous catheters usually is in between 2 % and 25 % per 1000 catheter days [1]. For patients the use of catheter access for total parenteral nutrition or infusion therapy presents an additional risk factor to underlying disorders (diabetes mellitus, AIDS). Administration of antibiotics reduces the risk to some degree [2]. On the seventh day after the insertion, starting from site infection the most dangerous catheterassociated sepsis, appears. As a consequence a substantially longer stay in hospital and a mortality increase up to 10 % is common [3,4]. Therefore much interest exists in the development of an infection-resistant material to prevent and reduce the number of catheter-related infections. There are several requirements for an inherent antimicrobial material: Broad spectrum of antimicrobial activity on the inside and outside of the catheter walls, sufficiently long antimicrobial effectiveness, excellent biocompatibility and specific mechanical properties for a given catheter application.