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About one in two people who wear ventricular assist devices are diagnosed with an infection. This is because of the thick cable for the power supply. Researchers at ETH Zurich have now developed a solution to alleviate this problem.
Andreas Kourouklis has received a Pioneer Fellowship from ETH Zurich to develop a new cable system for heart pumps. Image credit: Nici Lebküchner / ETH Zurich
For many patients waiting for a donor heart, the only way to live a decent life is with the help of a pump directly connected to their heart. The pump requires as much power as a TV, which it draws from an external battery via a seven-millimeter-thick cable. This system is efficient and reliable, but it has a major flaw: despite medical treatment, the point where the cable exits the stomach can be broken by bacteria.
ETH Zurich researcher and engineer Andreas Kourouklis is working to soon make this problem a thing of the past. In collaboration with Professor Eduardo Mazza of ETH Zurich and physicians at the German Heart Center in Berlin, Koroklis has developed a new cable system for heart pumps that does not cause infection. This is especially important because wireless methods of electrical delivery may not be available to patients in the near future. Kourouklis has received a Pioneer Fellowship from ETH Zurich to advance his technology.
Thin wires with craters instead of thick cables.
“The thick cable used in current ventricular assist systems creates an open wound that doesn’t heal and severely compromises patients’ quality of life,” says Koroklis. Scar tissue forms around the exit point with a limited blood supply. This not only affects the skin’s ability to heal itself, but also increases the risk of infection. As the outer layers of skin are injured and loosely attached to the flat surface of the thick cable, they move downward. As a result, bacteria can travel from the surface of the skin into deeper layers of tissue, often causing patients to struggle with infections and rehospitalizations.
Researchers at ETH Zurich have developed a technology to overcome this situation. Instead of powering the heart pump through a thick cable that is tougher than human skin, they use several thin and flexible wires with a rough, uneven surface. Kouroklis and his team compare their approach to the way in which human hair breaks through the skin without infection: “Highly flexible strands whose surface is covered with microscopic pits help the skin to heal,” Coroclis says. This is because the outer layers of the skin adhere better to these wires and do not move inwards. New tissue forms more quickly, and the skin is more likely to maintain a barrier against bacterial infection.
Water droplets form small puddles.
To create pits on the surface of the cables, a team of engineers led by Kourouklis and Mazza developed a new process that allows them to create very small, irregular patterns on surfaces that aren’t flat — something like Which was not possible before.
The method, currently patented at ETH Zurich, consists of coating flexible cables with a thin silicone layer and cooling them to minus 20 degrees Celsius. Thus the surface of the cables gets damaged. They are then placed in a condensation chamber, where tiny water droplets are pressed into the liquid layer of silicone, creating microscopic pits. “We can control the position of the pits on the cables by adjusting the humidity and temperature in the condensation chamber,” says Koroklis.
The challenge here is that pits can’t be too big or too small: if they’re too big, bacteria can build up in them and the risk of infection increases. If they’re too small, the skin doesn’t stay with them and moves inward – increasing the risk of infection. A classic optimization problem, which Koroklis and his team address through computational and experimental methods in tissue biomechanics and biomaterials.
Early tests confirm a low risk of infection.
Koroukles and his colleagues conducted preliminary tests on skin cell cultures before implanting both the old and thicker cables and their new cable system in sheep. The results make the ETH Zurich researcher optimistic: while thick cables with a flat surface caused severe inflammation, thin, flexible cables showed only mild inflammatory responses. No sheep sustained permanent injuries during the test.
Even more important: unlike thicker cables, sheepskin bonded better with new cables and hardly moved inwards. Accordingly, pitted thin cables do not cause infection in animals.
Corocles is currently working with medical device engineers and heart surgeons to improve the cable system. The aim is to bring the technology to market as quickly as possible. But before it can be used on heart patients, a series of tests will be needed on skin models, animals and eventually humans.
Source: ETH Zurich
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