Tech Briefs

The removable airway stent could revolutionize respiratory surgery.

Stents are cylindrical mesh tubes that can be placed in arteries or in the lungs to open blockages or areas that are narrow or weak. Traditional stents work well, but one disadvantage is that they must remain in the body. Researchers from the Norwegian University of Science and Technology, Trondheim, Norway, are testing a removable stent that can be used in the lungs.

The researchers say the new airway stent is the world's first knitted and uncovered self-expanding metal stent that can unravel and be completely removed. In a video describing the technology, inventor Erney Mattson says, “It sounds simple once you know about it, but basically we have tried different ways to remove [the stent]. But it wasn't until I saw a pair of old-fashioned rag socks that I had a Eureka moment.” Mattson is a professor in the NTNU Department of Circulation and Medical Imaging.

“A foreign object causes the body to react so that the vessel narrows again,” says Mattson. “For that reason, we have to remove it after it has done its job.”

Mattson tried several different methods but says he found inspiration in an old pair of socks. Mattson's stent is knitted, and like socks, it can be unraveled after it has been used. This allows the stent to be removed when it is not needed anymore. By leaving a thread sticking out, they can hold the stent and pull the thread to unravel it.

The new removable stent is made from self-expanding nitinol with a thread that extends beyond the tubular part. The end of the thread can be used to unravel the device and remove the stent. (Credit: Norwegian University of Science and Technology)

The researchers say the stent can be used in many different areas in pulmonary medicine. They say it is especially useful for patients who are short of breath due to narrowing of airways, particularly in the central respiratory tract. Tore Amundsen, also a professor in the NTNU Department of Circulation and Medical Imaging, envisions new applications in the future. “We have already thought about trying to do surgery via the airways. Being able to use a stent like this to temporarily open access to small tumors will be of great importance,” he says. “Then you can avoid doing open surgery.”

How It Works

The uncovered self-expanding metal stent is made of the memory alloy nitinol. In their paper, which was published in the European Respiratory Journal, they explain that the knitting technique makes it possible to produce the stent for a variety of indications because changing the thread thickness and mesh size can produce varying radial strengths, dimensions (length and diameter), and shapes, including Y-formation.

“It can therefore be customized and made to suit different tumor and patient characteristics. Therefore, it may respond to the clinical needs for individualized treatment, and in that case, it can be delivered within 24 hours,” say the researchers.

In this study, the stents were knitted with a nitinol thread having a diameter of 0.1 mm. According to the paper, the knitting pattern was adjusted to reach a radial force corresponding to commercially available stents. The stents were cooled down in wet ice before being packed into delivery sheaths, which were adjusted from standard vascular introducers with an outer diameter of 6 French.

The researchers note that the new stent was easily and accurately deployed in the central airways, and it remained fixed in its original position. It was easy to unravel and completely remove from the airways without clinically significant complications.

It is not yet clear when the stent will be ready for use in people, but Mattson is optimistic that it will be soon. “If everything goes smoothly, then at the end of 2017 or beginning of 2018, it should be possible.”

A video demonstrating the stent is available at here. For more information, visit here.