New Cable System for Heart Pumps Reduces Risk of Infection

Many patients awaiting a heart transplant rely on a life-sustaining pump connected directly to their heart. This pump, which has similar power consumption as a TV, is powered by an external battery through a seven-millimeter-thick cable. Although practical and reliable, this system has a significant drawback: the cable's exit point from the abdomen is prone to bacterial infection despite medical treatment. The thick cable of current ventricular assist systems creates a non-healing open wound, drastically affecting patients' quality of life. Scar tissue with limited blood supply forms around the exit site, hindering skin healing and increasing infection risk. The outer skin layers, wounded and loosely attached to the cable's flat surface, tend to grow downwards, allowing bacteria to penetrate deeper tissue layers and often leading to patient rehospitalization due to infections. But this problem could soon become a thing of the past, thanks to a new cable system for heart pumps that does not cause infections.

Engineers at ETH Zurich (Zurich, Switzerland), in collaboration with physicians from the German Heart Centre (Berlin, Germany), have developed a novel cable system for heart pumps. This system utilizes several thin, flexible wires with a rough, irregular surface, contrasting with the stiff, thick cables currently used. The design is inspired by how human hair penetrates the skin without causing infections. These more flexible wires, with microscopic craters on their surface, promote skin healing. The skin adheres better to these wires, preventing inward growth and fostering new tissue formation, thus maintaining an effective barrier against bacterial infection. The engineers have pioneered a process to create small, irregular patterns on non-flat surfaces to form craters on the cables' surface.

This method is patented at ETH Zurich and involves coating the flexible cables with silicone and cooling them to -20 degrees Celsius. In a condensation chamber, water droplets pressed into the silicone create microscopic craters. By adjusting the chamber's humidity and temperature, the crater positions on the cables can be controlled. The optimal crater size is crucial: too large and they may harbor bacteria, increasing infection risk; too small and the skin won't adhere properly, also raising infection risk. This optimization challenge was addressed through computational and experimental methods in tissue biomechanics and biomaterials.

Initial tests on skin cell cultures and implantation in sheep compared the new system with traditional thick cables. The results showed that while thick cables caused significant inflammation, the thin, flexible cables resulted in only mild inflammatory reactions. No sheep sustained permanent injuries, and importantly, unlike the thick cables, the sheep’s skin better integrated with the new cables without significant inward growth. The thin, cratered cables did not cause infections in the animals. The team is collaborating with medical device engineers and heart surgeons to refine this cable system, aiming for market launch. However, extensive testing on skin models, animals, and ultimately humans is necessary before its application in heart patients.

Related Links:
ETH Zurich
German Heart Centre

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