Ren ‘shaking up’ biofilm research

The use of antibiotics has traditionally been considered the gold standard in bacterial infection control—the more bacterial cells you kill, and the faster you kill them, the better. 

University of Tennessee, Knoxville Professor Dacheng Ren champions a different approach: engineer an antibiotic-free surface that prevents bacteria from establishing an infection at all. 

“It actually arose from an accidental discovery,” said Ren, who heads the Department of Biomedical Engineering. “About ten years ago, I gave some students a project that I thought would be simple and give straightforward results. However, the findings weren’t as expected. I got lucky to work with these really talented students. They paid attention to details, which helped lay a foundation for some exciting ideas that we work on today.” 

Ren had been studying biofilms, layers of bacteria that coat themselves in a matrix that both glues them to a surface and shields them from danger. Forming a biofilm makes bacterial cells 1,000 times less susceptible to antibiotics. 

Biofilm-forming bacteria are a major cause of medical device-associated infections for patients who need catheters, replacement heart valves, orthopedic implants, and other devices, sometimes resulting in severe illness or even death. 

What Ren’s students discovered is that bacteria don’t form biofilms on just any surface. Instead, they have a sophisticated means of sensing the topography of the surface they are on and can ‘decide’ whether to make a biofilm accordingly.  

“That inspired me to think, ‘Can we engineer a surface in a way that discourages them from attaching to it?’” Ren said. “Over the past few years, we learned how bacteria read the ‘map’ of a surface and how we can draw inspiration from nature to design better biomaterials.” 

Ren has spent the last several years working to engineer materials that bacteria find unappealing. In his previous role at Syracuse University, Ren and his research group pioneered “active topography”—flexible materials that can be manipulated through temperature changes or magnetic activation. The materials are tremendously effective at preventing biofilm formation and can even dislodge up to 99.9 percent of an established biofilm. 

Since Ren arrived at the University of Tennessee, his team of undergraduate and graduate students has continued to develop new active topography designs and applications. His lab is currently developing a prototype self-cleaning urinary catheter which Ren hopes will improve patient comfort and safety. 

“The surface of an implanted biomaterial can be a problem that causes biofilm infection,” said Ren, “but if we engineer it differently, it could instead be a solution.” 

The Problem with Static Surfaces 

The number of bacteria required to cause an infection on an implanted medical device is 1,000 times lower than the number needed to infect living human tissue. That’s part of the reason that over half of the healthcare-related infections seen in hospitalized Americans involve medical devices. 

“A lot of medical devices fail from infection because the devices use metallic or polymeric materials, which are static,” explained Ren. “But human tissues don’t stay static—they move and possess biological mechanisms that actively respond to invading microbes. That gives them a natural defense against bacteria that conventional biomaterials don’t have.” 

A few years ago, Ren’s group patented a material mimicking human cilia, which are the tiny, flexible protrusions on the surface of human cells that rhythmically sweep or “beat” to fend off infections. The team’s material is covered in micron-sized pillars that can be activated to beat in a similar rhythm, causing the whole surface to shudder like an earthquake—removing more than 99.9 percent of surface-attached bacteria and biofilms. 

In 2025, Ren and his colleagues at Syracuse further improved the ciliated (cilia-covered) material by coating it in mucin, a protein that helps human cells repel bacteria. Now he and his group at UT are working to integrate active topography into next-generation, microbe-resistant medical devices. 

Longer-Term Medical Devices  

Urinary catheters are used to drain urine when patients are unable to visit the bathroom or control their bladders, such as during and after surgery or because of certain medical conditions. Catheters can be rapidly colonized by biofilm-forming bacteria, so they need to be changed out every two to four days; every year, the US goes through about 75 million of them. Most patients will recover within days, and their catheters will be removed without an issue. 

“But we’re thinking about the patients who will need this long-term,” Ren said. “They may need (a catheter) for months, or some people need it for the rest of their lives.” 

Changing a catheter is traumatic; beyond being a painful process, it causes irritation to sensitive tissues, which itself can lead to infection. If patients aren’t willing or able to get their catheters changed frequently enough, bacterial infections can establish in the urethra or bladder. As bacterial biofilms accumulate, mineral deposits can form and clog the catheter. The infection may also spread to the kidneys and, in severe cases, enter the bloodstream and lead to life-threatening sepsis. 

However, building a catheter that can regularly dislodge bacteria and biofilms could extend the safe usable life of a catheter from days to weeks. Ren’s team is currently working to create a prototype catheter lined with the ciliated active topography material, hoping it will significantly improve both patient comfort and health outcomes. 

“The more I think about it, the more I realize that surface motion can help us create better medical materials,” Ren said. “Life is dynamic, not static, and a static surface is unlikely to give long-lasting functionality. We are excited to continue exploring this new direction with bioinspired active topography and can’t wait to see what the future holds.”