Coatings & surface treatment
catheters and create the environment for bacteria to grow. The bio-inspired coatings I had worked on were great with proteins, and my ability to make such materials complemented Ana’s understanding of proteins perfectly.”
An infused biocompatible polymer, inspired by the Nepenthes pitcher plant, moves more liquid up from within the polymer to replace it when it is removed.
biomedical engineering at the University of Maine. “Antibiotics work well, but the emergence of antibiotic-resistant organisms means that we constantly need different or stronger treatments to kill the infection. This may be a slow-moving problem, but it is a very serious one.” “Often, there are multiple microbes, so when you kill one you are just making room for others,” she adds. “As the population ages, more people need long-term catheterisation, and it is not practical to change the catheter every day. If you have a catheter for 30 days, the probability of infection is 100%, so it is clear that we need new solutions.”
“Antibiotics work well, but the emergence of antibiotic-resistant organisms means that we constantly need different or stronger treatments to kill the infection. This may be a slow-moving problem, but it is a very serious one.”
Caitlin Howell
Fortunately, Howell, who did her post-doctorate training in bio-inspired materials, recently attended a conference hosted by the US National Institutes of Health (NIH) to connect researchers who could generate ideas to combat catheter-associated urinary tract infections (CAUTI). There she met Ana Lidia Flores-Mireles, Hawk Family assistant professor of the Department of Biological Sciences at the University of Notre Dame, and the door to innovation opened.
“These infections are very common and come with a terrible cost in terms of damage to patients and their families,” Howell observes. “I met Ana, who is an up-and-coming leader in CAUTI and who had done some work on proteins that adhere to
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A slippery solution Howell’s post-doctorate studies at Harvard saw her work on the concept of liquid coatings to repel contaminants such as oil. But she extended the range of contaminants to encompass the microbes that take root on the wet surfaces inside the body. Working with Flores-Mireles, she devised a novel liquid surface coating for human catheters, which can help reduce the protein deposition that leads to infections of the urinary tract and bloodstream. “I try to understand the mechanistic interaction between pathogens and their host,” explains Flores-Mireles. “I asked why the infection rate with catheters was so high, but clinical studies don’t give a mechanistic perspective. Also, I had seen different pathogens – Escherichia coli, Candida and many others – that don’t cause infections if there is no catheter and no biofilm.
“So, we had to look at what is different about catheters that allows the build-up of pathogens and why existing anti-microbial coatings were not preventing infections when they don’t normally grow in human urine,” she adds. “Biofilms don’t work in that environment, so something in the patient is making the pathogens when a catheter goes into the bladder.” The surface of the bladder, which is small but flexible, can be easily scratched by a catheter, as a rigid new pair of shoes can cause blisters on your feet. Constant irritation causes the protein Fibrinogen, a clotting factor, to be released in high volumes. These proteins coat the catheter, rendering the anti-microbial film ineffective because it is no longer coming into contact with the pathogens.
“A silicone catheter does not provide a good platform for preventing infection,” says Flores-Mireles. “Instead, it gives a good platform for the accumulation of proteins that enhance microbial colonisation.” The pair’s research, funded by a five-year NIH grant exceeding $2m, investigates how protein adhesion influences bacterial colonisation on commercial catheters, with a view to further developing liquid-infused catheter surfaces to reduce protein deposition. Helpfully, around the time the two started working together, Howell had become aware of the work Harvard University’s Wyss Institute was doing on Slippery Liquid-Infused Porous Surface (SLIPS) technology, which creates omniphobic, slippery
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