What is a stent and how can it help save lives?

According to Wikipedia, German hospitals insert more than 500.000 stents into their patients each year to keep blood vessels open, dilate or support them.

A company specializing in covered stents is Bentley, based in Hechingen, Germany. In charge of showing how simulation can be used to optimize quality and the useful life of small “salvation carriers” (stents).

Founded in the «Medical Valley»

The Hechingen region is the mecca of medical technology and is confidently called the “Valley of Medicine”. This is also where Miko Obradovic and Lars Sunnanvaeder founded the Bentley company in 2009 to bring Obradovic's idea to the market.

Sunnanvaeder had already founded several companies in the field of medical technology. Bentley currently manufactures approximately 80.000 endoprostheses and employs 187 people.

How a stent graft works

Endoprostheses are medical implants that are primarily used to keep hollow vessels and organs open. They are tubes of braided or cut wire that are crimped in a state of radial compression into a balloon, which in turn sits on the tip of a catheter.

Using a sheath and guide wire, the surgeon pushes the catheter through a small incision in the affected vessel until the stent is at the site where the vessel is to be dilated.

The balloon is then inflated, the mesh expands, and the diameter of the stent increases until the desired size is reached. After this, the balloon is deflated to remove the catheter.

The stent remains in the vessel, covering it and supporting it from the inside, so to speak. A special form is the covered stent, in which the metal mesh is covered with a sheet-like material to form a closed tube.

This form is used, among other things, to repair aneurysms. An aneurysm occurs when the wall of a vessel weakens and a bulge forms in which a large amount of blood can accumulate. If this lump bursts, the patient can die in a very short time.

The stent bridges the weakened area of ​​the vessel and relieves pressure on the bulge, preventing it from bursting.

The stent family is growing

Based on their ideas, the founders of Bentley initially launched a covered stent, around which an entire family of covered and uncovered stents has successively developed to date.

Bentley endoprostheses are manufactured primarily from cobalt-chromium steel, but also from shape memory alloys.

Shape memory alloys are used, for example, in joints where high flexibility of the endoprosthesis is required. The diameter of the endoprostheses used varies between 2,5 and 30 millimeters, depending on the application area.

Since 2018, a trial has been underway with a stent system that can be used in babies and can be extended several times as the child grows.

Approval takes time

The approval process for these medical implants is long; It may take several years for a product to be approved for marketing. stent. Therefore, it is important to work very carefully in the development phase to avoid problems arising in the approval phase that compromise or even prevent the market launch.

Stents must reliably exert radial force to keep the vessel open while also being flexible enough so the surgeon can easily reach hard-to-reach vessels in the body.

The change in blood pressure also occurs in the arteries: with each heartbeat, the vessels expand and then contract again. A stent It must be able to withstand the resulting forces for at least ten years without, for example, a strut breaking, which would cause complications.

Another development challenge is that the crimped stent must expand evenly and precisely when placed in the vessel to function optimally.

Therefore, service life tests are part of the standard repertoire of tests that a new design must withstand. Material fatigue can be very well calculated using digital simulation, which in turn is faster and cheaper than (real-world) physical testing.