Enhanced biocompatibility of stent coatings

Narrowing of blood vessels increases your risk for stroke or heart attack. To prevent this from happening, stents are used to help widen the clogged arteries. Yet in some cases, the implant may prompt undesirable effects. An IKTS research project has now improved the biocompatibility of stents.

COMPAMED-tradefair.com spoke with the Project Leader, D. Eng. Natalia Beshchasna, about the latest status of the research project.

Dr. Beshchasna, your team has developed an enhanced stent coating. Could you briefly describe conventional stent coatings?

Dr. Natalia Beshchasna: There are a variety of stents available on the market and in research. On the one hand, you have metal stents made of stainless steel, cobalt-chromium alloys or nitinol. These types of stents don’t have any coating or covering. Unfortunately, there is a greater risk of complications with these stents. Stent implantation may cause an inflammatory response or constriction of the blood vessels for example. Coatings are used to prevent these types of complications. The idea here is to improve the biocompatibility of the implants. One coating option uses titanium oxynitride, a compound of titanium, oxygen and nitrogen. This type of coating is one of the best solutions and has also been used by our team.

Does this mean you improved an existing stent coating?

Beshchasna: It's true, this idea is not new per se as there are already several products available on the market. However, there is still no perfect homogeneous coating out there. Until now, the complex structure of the stents made even coating coverage difficult. What’s more, the adhesion of coatings for stents is in parts challenging to achieve and still needs improvement. We have tried to improve the quality of this coating.

It is a fact that the ratio of oxygen to nitrogen in the coating significantly affects its properties, which is why we tried to find an optimal ratio of the two gases. We created different coatings and examined the mechanical properties, cell compatibility and adhesion at the stent surface to identify the coating with the perfect properties. Our results show that the optimal ratio of oxygen to nitrogen is three to five.

Apart from an enhanced coating, we also aimed to develop an improved coating process for the stents. We made a series of improvements in this case, including technological advances in the deposition process. This improves the biocompatibility of the stents. We succeeded in increasing the degree of stent coverage by ten percent. As a result, the coating now covers 90 percent of the stent, up from 80 percent.

How do you test the stents and how long do these tests take?

Beshchasna: The stents undergo mechanical testing, cell compatibility testing, and tests to determine whether they can withstand exposure to a constant stream of blood-like liquids. For example, we place the stents in an artificial blood vessel: a kind of tube that can expand like a blood vessel. The test examines the impact of various factors on stent stability, including exposure to varying temperatures, pressures and flow speeds. Obligatory tests can take up to three months in our setting.

Stents remain inside a patient’s body for much longer. Do you also conduct long-term experiments?

Beshchasna: We conduct preliminary tests in this case. Needless to say, those are not sufficient to warrant clinical application. Authorization requires further testing and clinical trials. However, our research project did not focus on these types of investigations. We centered on a physicochemical characterization of the stents and achieved this by means of in vitro experiments.