Thin but Powerful

It does not matter if one takes a close look or not. Amorphous carbon films are a few hundred times thinner than the finest single human hair and is invisible to the naked eye. Regardless of their fineness, they are able to protect huge turbines or large blades. „Originally, carbon films have been used to coat metal tools in order to reduce abrasion. At the beginning of the 90s, it was discovered that the films are biocompatible“, says Lisa Kleinen, physicist from the Institute for Thin Film Technologies at TU Kaiserslautern in Germany.

Since then, amorphous carbon films are also being applied in medicine: They cover knee and hip implants, artificial heart valves or electrodes. Why? Because medics have a common problem with implants and the human body: „In medicine you cannot do much about the actual material of an implant since it needs to fulfill certain requirements - a catheter needs to be flexible, an artificial joint very stable“, Kleinen explains. Therefore, researchers started to concern themselves with surfaces - the interface between implant and body.

„You can apply coatings to materials and vary their properties so that an implant better adheres to bone or an ingrowth in blood vessels can be prevented, for example“, explains Kleinen who together with a researcher at the University Hospital in Bonn works with amorphous carbon films inhibiting bacteria to settle on urological stents.

A crust may cover the stent raising the risk for infections

These stents are being used for ensuring that urine passes from the kidneys to the bladder without problems. The problem that may arise: Organic biofilms settle on the stents and may develop into cristalline bacterial films. That means that a crust begins to cover the stent raising the risk for infections and the stent needs to be exchanged.

„We coat pigtail catheters made of polyurethane with a special film“, says Kleinen. „That carbon film is produced with a previously determined set of parameters that ensures the repellence of bacterial films.“ Amorphous carbon films consist of carbon that is bound either in a planar or tetrahedral manner whose proportions determine certain chemical and physical properties. The mixture of differently bound carbon is influenced by parameters such as pressure or gas flow when creating the films.

The reason why the carbon film developed at the Institute of Thin Film Technology prevents the incrustation of stents is not known. „We are at the moment trying to determine the mechanism. It works but how exactly - I cannot say. However, it will not take much longer until we understand the whole story“, says Norbert Laube, head of the Department for Experimental Urology at the University Hospital Bonn, who tested the stent with about 50 patients so far. „We experienced that the time before stents had to be exchanged doubled.“

The stents have been commercially available for a year. „The usage of the stents, however, has not become a standard procedure yet. Years will pass before that happens“, Laube guesses. He is a co-developer of the product. „It depends on the marketing strategies of the company producing the stents and on the attitude of medics.“ And, of course, it depends on the price, too: The stents are expensive due to vacuum processes needed for the production of the films.

Amorphous carbon films at the beginning of possibilities in biomedicine

„The technology is not inexpensive“, confirms Dr. Michael Stüber, research assistant at the Institute for Material Science at the Research Centre in Karlsruhe, Germany. Even so, coating technologies have long developed into a „big thing“. „Many, many key technologies include coating technologies“, says Stüber. That starts with the whole semiconductor technology and solar plants and ends with the automobile industry.

Regarding research in the area of thin films and medical technology interdisciplinarity is of special importance. „Specialists from different disciplines need to be brought together since we need technical understanding as well as biological or chemical knowledge“, Stüber stresses. Amorphous carbon films are at the beginning of possibilities in biomedicine. The Research Centre Karlsruhe and many others are therefore preparing for the future by offering more courses which require and support an interdisciplinary background. A very popular one: Biomaterials.

Wiebke Heiss