3D plasma coating technique prevents stents from clogging

Materials World magazine
1 Jul 2007
Plasma-coated stent

Researchers at the University of Ulster, UK, have developed a 3D plasma coating technique for stents to prevent clogging.

Stents are tubular medical devices made from stainless steel or cobalt chromium alloy. They are used to keep arteries open and blood flowing. But the structures have been known to develop neointima, where thick muscle tissue grows over the surface, leading to the blood vessel narrowing again.

‘It is difficult to establish with confidence what causes problems with stents,’ says Professor Paul Maguire of the Nanotechnology and Integrated Bio-Engineering Centre at the University of Ulster, UK. ‘We do know that the materials, the quality of their surfaces (for example, roughness, local chemistry, oxidation and grain structure), and coatings will have an impact.’

Creating a stent surface that is inhospitable to tissue growth has become an important research goal.

According to Maguire, several groups are developing plasma coatings for stents, but such work is primarily focused on coating materials, rather than exploring the plasma technology itself. He says that materials such as carbon, ceramics and platinum have shown promise in preventing neointima on stents, ‘but transferring bulk or thin film from a flat substrate to a [curved] stent and then expanding it is a serious challenge’.

While Maguire cannot be too specific about how his team’s plasma technique works, he explains that it bombards the stent with high intensity plasma on all sides, allowing the coating material to cut through the surface and bond directly with the device, creating a flat, smooth film that is less than 50nm thick.Traditional plasma methods have had difficulty adhering to structures of different shapes, a problem that Maguire says his group has overcome.

‘Surfaces are not uniform, they normally [have] different textures and bumps. We make our atoms go through that surface, so it avoids taking hold of the coating.’

The greatest achievement of the 3D plasma technique, says Maguire, is its versatility. The equipment design allows for uniform coating, a wide energy range and multiple component handling. It can work with highly ionic to high radical densities that are hydrogen-free or are hydrogenated. It also allows for more controllable batch coating for volume manufacture. Work will need to be undertaken with individual manufacturers on specific stent designs.

‘There are a lot of novel stent designs planned. We hope to offer an enabling technology for many of them,’ adds Maguire.

The Ulster team has mainly been working with amorphous and dense carbon coatings. It has created its own coating that is microcrack and nanoporosity-free, making it stable in the human body’s corrosive environment. However, Maguire believes the plasma system will work with any suitable material.

‘Our attitude is that the medical device companies will tell us what materials they are interested in developing, and we will provide an advanced and dedicated manufacturing technique to get the best surface quality within the stent.’

The group is hoping to commercialise its technique within the next few weeks.