Stent device recruits nearby cells to prevent infection

Stents, which are essentially meshed wire tubes, are most frequently used by surgeons to widen narrowed blood vessels and maintain blood flow in people with cardiovascular disease. Stents can also be used to treat pathological constriction of the windpipe.

This kind of respiratory stenosis, which may be caused by tumours, chronic infections or congenital deformities, can be life threatening.

However, complications of stent placement can occur and include a shifting of the implant, which can partially or completely obstruct the respiratory tract and bacterial infection, triggering pneumonia. One key factor behind these complications is that the stents have no barrier-forming cells of the kind usually present in the respiratory system, whose task is to fend off bacteria and inhaled substances such as particulates.

Noting this, a team of scientists at the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB) in Stuttgart, together with clinicians at a nearby hospital, initiated the ‘REGiNA’ project, the goal of which was to develop surface coatings that enable the stents to be incorporated into the surrounding tissue.

For the structural base-layer material of the stent, they chose polyurethane made by Leufen Medical.

‘Polyurethane is a biocompatible material that offers new possibilities in medicine,’ Dr Martina Hampel of Fraunhofer IGB told The Engineer. ‘It is degradable without producing any toxic substances and also shows variable mechanical properties, which is very interesting especially in the field of tissue engineering.’

In the ensuing tests, a wide variety of different coatings were applied to the polyurethane (PU) film. In addition to synthetic polymers composed of organic acids, the researchers also tried out biological proteins such as fibronectin and type-I collagen. The coating was modified again using plasma technology, with vacuum-ionised gas being used to treat the surface. Untreated PU film was used for control purposes.

‘The plasma treatment induces a higher “wetability” of the surface — or hydrophilic properties — so it might be easier for cells to adhere,’ added Hampel. ‘It is also possible to integrate different chemical groups on the surface such as amino, aldehy, carboxy or hydroxyl groups, which also make it easier for the cells to adhere.’

In order to find out which of the surface coatings was the most suitable, they brought human primary tracheal epithelial cells into contact with the films in cell culture vessels, looking for signs of adherence.

The respiratory cells proved to be more vital on bioactive films rather than on ones treated with plasma, while, by contrast, polymer-coated film turned out to be ‘completely useless’, according to Hampel.

‘We used proteins such as collagen, laminin and fibronectin — proteins that also occur in the extracellular matrix, the surrounding area of the cells in a tissue. So our aim was to simulate this natural environment to stimulate the cells to grow on this material.’

The team will now look for ways to scale up the protein deposition technique so it might be applied to other devices.

‘We hope that, within just a few years, our well-tolerated, cell-compatible surface coatings will be used for other biomedical prostheses such as pacemaker leads, tooth implants and replacement joints,’ said Hampel.