Weird Flex, Not OK for Medical Devices

Flexibility is helpful for devices like catheters and implants. But when bending opens up tiny cracks, it sets the stage for infectious bacteria.


When we make medical devices out of flexible materials like silicone, it’s because they’re designed to bend. But it’s also critical to prevent them from becoming infected, and new research from the University of Toronto shows that these two goals might conflict with each other.

They showed that when medical devices like catheters or implants are bent, the side under tension opens up microscopic cracks, creating tiny havens for microbes hoping for a home. Their study was published in Scientific Reports.

The team used commercial-grade medical tubing for their experiments, exposing bent pieces to biofilm-forming Pseudomonas aeruginosa bacteria. After giving them some time to grow, they added a fluorescent dye to help look for them under a microscope. They found that four to five times as many grew on the outside of the bend where the cracks had formed, compared to the compressed side. The authors hypothesize that the open cracks may offer rougher surfaces for the bacteria to stick to.

When they tried treating the tubing much more gently, such as by simply wiping pieces with laboratory tissue, they still found microscopic scratches that led to hotspots for bacterial colonization. They even found microcracks on devices straight out of the package, suggesting that the commercial manufacturing process may also play a role.

“The formation of microbial biofilms on these materials is common, but we were surprised by the degree to which bending silicone, and other rubber materials, causes these cracks to reversibly open and close — and how big a difference they make in terms of biofilm formation,” said principal investigator Ben Hatton, associate professor of materials science and engineering, in a press release.

When biofilms form, they are more protected from antibiotics or the immune system than individual microbes would be, and that can trigger longer hospital stays or higher risks of persistent infection. Knowing this, surgeons should keep a close eye on where implants are bent during use because the side under tension is where infections are most likely to begin; even if defects had formed previously, cracks in the concave side tend to seal up under compression.

Flexibility is an important feature in the design of many medical devices. In addition to this enhanced awareness of where infections tend to take hold, Hatton’s team is also looking for ways to treat implantable medical devices to reduce cracking or hide the defects from opportunistic microbes. Hopefully these innovations will one day reduce infection risks for patients.

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Karyn Ho is a science animator and engineer who thrives at the interface between science, engineering, medicine, and art. She earned her MScBMC (biomedical communications) and PhD (chemical engineering and biomedical engineering) at the University of Toronto. Karyn is passionate about using cutting edge discoveries to create dynamic stories as a way of supporting innovation, collaboration, education, and informed decision making. By translating knowledge into narratives, her vision is to captivate people, spark their curiosity, and motivate them to share what they learned.