Cardiovascular stents are special implants used to widen blood vessels that have become constricted as a result of calcium deposits. In some cases, the body’s immune system can reject these implants in a process known as foreign-body reaction. In a joint project with partners, Fraunhofer researchers in Dresden have now developed enhanced coatings that substantially improve the bio-compatibility of stents.
When blood vessels become narrowed as a result of calcium deposits, there is a real risk of an infarct or stroke. In such cases, physicians will prescribe the insertion of stents. These are fine tubes of stainless-steel mesh. Once inserted, they are expanded in order to keep the blood vessel open. Around one-quarter of all patients display an immune response with undesirable effects such as inflammation, a rejection of the stent as a foreign body or its encapsulation with tissue. These reactions mean that the blood vessel is more likely to become constricted again. In response, manufacturers are now starting to coat stents as a way of increasing biocompatibility. Typical coatings include titanium oxynitride, a compound of titanium, oxygen and nitrogen. However, the coating process does not always produce perfect results: there may be gaps in coverage and variations in coating thickness. So while coatings can reduce the risk of foreign-body reaction, they cannot completely eliminate all such complications.
In a collaborative project with Polish stent manufacturer Balton, the Russian company VIP Technologies and the University Politehnica of Bucharest, a research team from the Fraunhofer Institute for Ceramic Technologies and Systems IKTS has now been able to enhance these stent coatings and, in the process, substantially improve their bio-compatibility. The project is jointly sponsored by the German Federal Ministry of Education and Research (BMBF). “Biocompatibility depends on a range of material properties, including roughness of the surface, wettability and the chemical composition of the coating,” explains Dr. Natalia Beshchasna, project leader and scientist at Fraunhofer IKTS. “By enhancing the coating process, we’ve been able to fine-tune these parameters, which in turn has improved the biocompatibility of the stents. Specifically, we’ve been able to increase the degree of coverage by ten percent – the coating now covers 90 percent of the stent, up from 80 percent.”