[Coating with plasma-deposited functionalized diamond-like carbon to decrease encrustations on urological implants]. / Plasmadeponierte funktionalisierte Kohlenstoffschichten zur Minderung von Inkrustationen auf urologischen Implantaten.

The double-J stents used today for palliative artificial urinary diversion very often show extreme formation of encrustations, even a short time after implantation. Despite increased scientific material development, the complication rate has not really been strongly influenced. Grant-aided by the German Federal Ministry of Education and Research, we chose a new interdisciplinary and translational approach by coating standard stent materials with plasma-deposited amorphous diamond-like carbon. These stents show clearly reduced rates of encrustation in vitro. Ongoing clinical trials demonstrate a further enhancement of this effect in vivo. The underlying mechanisms are being investigated by extending the established in vitro model, thereby pushing research in this field to a new level.

[Plasma-deposited carbon coating on urological indwelling catheters: Preventing formation of encrustations and consecutive complications]. / Plasmadeponierte Kohlenstoffbeschichtung auf urologischen Verweilkathetern: Vermeidung der Ausbildung von Inkrustationen und konsekutiven Komplikationen.

BACKGROUND: Any material placed in the urinary tract is susceptible to the formation of encrustations of crystalline bacterial biofilms. These biofilms cause severe complications in some cases. The strategies used so far for reduction of these complications by surface modifications of the implant material failed to show the expected results. PATIENTS AND METHODS: In this study, we investigated amorphous carbon coatings (a-C:H) for their ability to effectively reduce or to repress the progressive formation of infection-enhancing crystalline biofilms as new functional surface coatings. In nine patients suffering for several years from stenting, a-C:H-coated ureteral stents were tested in treatment attempts. The current replacement intervals amounted to a mean of 77 days; the principle cause for early replacement was massive stent encrustations associated with symptomatic urinary tract infections. RESULTS: In total, 20 coated ureteral stents were tested spanning indwelling times between 3 and 4 months. No stent-related complications occurred. In all cases extraordinarily facile handling, less pain during replacement, and markedly increased tolerance were observed. Symptomatic urinary tract infections were reduced by more than 50%. The stents remained virtually free of encrustations. CONCLUSION: a-C:H coatings are a novel strategy leading to an enhancement of long-term applicability of ureteral stents and catheters and to improved patient comfort.

[On the uncertainty of measurements illustrated by the BONN Risk Index]. / Uber die Unsicherheit von Messwerten am Beispiel des BONN-Risk-Index.

Every result of a measurement is subject to error. This error is inevitably caused by inaccuracies of the devices used and by environmental influences. For correct evaluation of a measurement result, this error must be estimated as exactly as possible. In kidney stone research and urolithiasis treatment, risk indices are applied to determine a patient's health status [e.g., AP(CaOx), RS(CaOx), BRI]. These operands (indices) combine important physical and chemical parameters of a certain disease pattern in a theoretically or empirically obtained mathematical formula. The index-related total error resulting from the single errors of the individual input parameters might be calculated with the Gaussian error propagation method. This method takes into account that individually determined parameters contribute differently to the total result. Due to this, summation of the various specific errors is insufficient. Instead, they must contribute to the total error depending on their individual weight. In medical borderline cases, knowledge of the value of this error may improve diagnosis since critical observation of an acquired value helps to avoid false interpretation. Using the BONN-Risk-Index (BRI) as an example for determination of the urinary calcium oxalate crystallization risk in native urine, the method of error calculation is demonstrated in detail and the advantages of including discussion of error in method development are discussed.

[Can the cutting performance of trephines still be improved?]. / Kann die Schnittqualität von Trepanen noch verbessert werden? Anwendung nanotechnologischer Verfahren zur Herstellung von Trepanen mit diamantähnlichen Schneidkanten.

PURPOSE: Today, for the preparation of donor and recipient cornea during keratoplasty either single-use or reusable metal trephines are commonly used although excimer and femtosecond laser systems are available. Due to the surgical techniques as well as the configuration of metal trephine's cutting edge irregular corneal surfaces may be induced. These will result in a postoperative astigmatism. Contemporary manufacturing processes do allow for the production of minimal cutting edge diameters (400 nm -- 1 microm), however, this is related with a reduced mechanical stability of such delicate cutting edges. It has been observed that the cutting edge of metal blades is immediately bent with the first exposure to tissue. As a result, the cutting forces are increasing and the wound configuration is negatively effected. Due to the complex geometry of trephine cutting edges, no diamond trephines are currently available. We are investigating the cutting performance of conventional trephines that were modified using nanotechnology. METHOD: Different metal trephines were characterised using a scanning electron microscope (SEM). The diameter of the cutting edge was measured. Pig cornea were studied histologically after trepanation. Selected trephines were ion-forged in a modified PVD (physical vapour deposition) reactor using highly accelerated ions which are concentrated by magnetic fields at low temperature. The consecutive processing steps were controlled by SEM analysis of the cutting edge diameters. Randomly chosen areas of treated trephines were analysed. After processing the trephines, pig cornea were cut and analysed by histological and SEM examination. Additionally, the relevant mechanical cutting parameters of untreated as well as treated trephines were measured when penetrating into a PU (polyurethane) foil. RESULTS: Preliminary microscopic analysis already reveals differences in the quality of the cutting edges. The nanotechnological modification of the cutting edges does not result in larger diameters. Compared with the initial cutting edges, the optical analysis of the modified trephine cutting edges reveals subjectively smoother surfaces. The force measurements prove a reduction of cutting forces for the treated trephines compared to the untreated ones. The SEM analysis show for the cornea treated with the modified trephines a subjectively smoother surface. Histology reveals that the surfaces of the treated cornea do not exhibit a smooth and unidirectional structure. This divergence became larger when untreated trephines were used. The mechanical characterisation of the treated trephines resulted in harder and longer-lasting surfaces. DISCUSSION: The newly developed ion-forging of trephines in combination with nanostructured carbon coatings yield complex cutting edges of higher stability with diamond-like properties. This study shows that the performance of laser trepanation cannot be reached; however, the use of nanotechnology can further improve manual trephine techniques.