In disorders of the urinary tract indwelling catheters in the lower urinary tract help patients to discharge their urine. However, sometimes the thin tubes are coated after as little as a few days with an infectious crust of bacteria and crystals, with unpleasant consequences: one third of all infections which patients contract in hospitals originate as the result of catheterisation of the lower urinary tract. For the German health care system this means additional costs of 500 million Euros annually.
'Up to now there has not been any effective way of preventing bacteria from entering the urinary tract via the catheter and thereby triggering urinary tract infection,' the Bonn researcher Dr. Norbert Laube explains. Several species of bacteria cause a steep increase in the urine pH value by their metabolism. The result is that salts and other substances which are normally found in suspension in the urine are precipitated and form a deposit. After only one week some catheters look like the inside of a coffee machine which has not been de-scaled for years. 'Anyone can imagine how unpleasant the presence and even more the removal of a catheter which is thus coated with a hard crust must be for the patient,' Dr. Laube adds. To make matters worse, 'the crystalline biofilm of bacteria makes many kinds of medication less effective; even when antibiotics are used the infection is then often difficult to combat.'
In addition to urinary catheters there are also what are known as ureter splints (stents), which are inserted from the bladder right up to the kidney. For example, in ureteroliths or cases of cancer they ensure that the urine can be discharged without obstruction from the kidney to the bladder,' Dr. Laube explains. The stents sometimes stay in the body for weeks or even months. Some patients have to use these ureter splints all their lives. If crystalline deposits develop, this can lead to life-threatening consequences.
Diamond-like carbon coatings could help
Together with Lisa Kleinen from the Institute of Thin Film Technology of the Technical University of Kaiserslautern and Dr. Karin Schenk of the company NTTF (New Technologies in Thin Films), Dr. Laube is presenting initial research findings at the forthcoming MEDICA medical fair which show how it may be possible to avoid this incrustation. This team of physicists have coated catheters and ureter stents with an extremely thin layer of diamond-like carbon. DLC-coated surfaces do not react chemically with their environment; they are hardwearing, can be sterilised and reduce friction.
Even after three months in the body the coated stents show virtually no incrustation,' says Dr. Andreas Meißner, Urological Resident Physician at Bonn's University Clinic. 'In addition, the catheters are easier to insert or replace than catheters currently on the market.' Patients who were treated using these specially coated stents felt that the procedure was substantially less unpleasant. Moreover, the catheters needed to be replaced less often. Dr. Laube stresses, 'Apart from the aspect of incrustation, the greater comfort for the patient is an important step forward in itself.'
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