Study could point way to reducing scar tissue around implants

Over time, scar tissue slows or stops implanted bioelectronics. But new interdisciplinary research could help pacemakers, sensors and other implantable devices keep people healthier for longer.

In a paper published in Nature Materials, a group of researchers led by University of Chicago Pritzker School of Molecular Engineering Asst. Prof. Sihong Wang outlined a suite of design strategies for the semiconducting polymers used in implantable devices, all aimed at reducing the foreign-body response triggered by implants.

The immune system is primed to detect and respond to foreign objects. In some cases, the immune system might reject lifesaving devices such as pacemakers or drug delivery systems. But in all cases, the immune system will encase the devices in scar tissue over time, hurting the devices’ ability to help patients.

“A lot of research groups are making very novel designs of implantable devices, but almost every research group is using a similar model and is facing a similar challenge: long-term implantability,” said Pritzker Molecular Engineering postdoctoral researcher Seounghun Kang, a co-first author of the paper.

Working through scar tissue

A polymer—any polymer—is built around a chemical “backbone” with a series of branching side chains building out the rest of the material’s structure. 

To make polymers that triggered less of an immune response when implanted in live tissue, the team took a two-pronged approach. They both incorporated the compound selenophene into the backbone and added other immunomodulating materials to the side chains.

“Based on these two strategies, we developed these new materials that not only exhibit good biocompatibility, but also maintain the good electrical performance needed for a bioelectronic device,” said co-first author and Molecular Engineering PhD student Zhichang Liu.

In tests on mice, the team, including lead first author Nan Li, PhD’23, found as high as a 68% decrease in collagen density—the scar tissue that builds around pacemakers and other devices, reducing their efficiency over time.

For addressing the grand challenge of foreign-body responses for implantable devices, this research complements a hydrogel semiconductor the Wang research group created last year to better interface body and machine. Both were funded through an NIH Director’s New Innovator Award Wang received in 2022.

While the hydrogel semiconductor research changed the physical structure of implanted devices, this new work changes their chemistry so that they do not trigger as large an immune response.

“Overall, this comes from our goal of addressing a grand challenge, a universally existing challenge for any kind of implantable device,” Wang said. “When you insert any foreign material into the human body, the immune system will start to attack it. First, this is generating side effects in patients. Second, it is also affecting the long-term stability of the device.”

This means that, over time, the devices that regulate heartbeats, record brain signals, take vital readings, and release insulin and other medications become less efficient and, in some cases, stop working entirely.

“You need the biological signals to be able to efficiently go from the organ to the device to get effective recorded,” Wang said. “But the foreign body response is generating a layer of dense fibrotic tissue, like a scar. That scar layer is insulating the device, encapsulating it to prevent the efficient transport of biomolecules or other types of signals.”

Unique strengths

The team will next focus on improving the long-term stability of the new materials while continuing to work on ways to decrease the immune system’s response when a foreign body is implanted, Liu said.

"During this research, we also found some different strategies to deal with the foreign-body response, such as reducing the reactive oxygen species,” she said. “That is also part of this very important research.”

For Wang, the ability to better connect electronics and the human body reflects a larger interface—the connection between material science and immunology. He credited the school's interdisciplinary approach, organized by research themes rather than siloed university departments, for allowing creative breakthroughs to flourish.

“This is one of the unique strengths of UChicago Pritzker Molecular Engineering,” Wang said. “When these two research spaces, these two disciplines, start to interact at a deep level, what kind of new technological frontiers could be generated?”

Citation: “Immune-compatible designs of semiconducting polymers for bioelectronics with suppressed foreign-body response,” Li et al, Nature Materials, April 17, 2025.

Funding: US National Institutes of Health Director’s New Innovator Award, National Science Foundation, US Office of Naval Research.

—Adapted from an article first published by Pritzker Molecular Engineering.