Semiconductor Polymer Design Strategies Points How to Reduce Scar Tissue Around Implants

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

The paper published in Nature Materials is a group of researchers led by the University of Chicago Pritzker School of Molecular Engineering Asst. Professor Sihong Wang outlined a set of design strategies for semiconducting polymers used in implantable devices, aimed at reducing foreign body reactions triggered by implants.

The immune system is ready to detect and respond to foreign bodies. In some cases, the immune system may reject lifesaving devices such as pacemakers and drug delivery systems. However, in all cases, the immune system wraps around the device of scar tissue over time, damaging the device’s ability to help the patient.

“Many research groups have very novel designs of embedded devices, but almost all research groups use similar models and face similar challenges. They face long-term embedding.”

Working through scar tissue

Polymers (any polymers) are built around a chemical “backbone” with a series of branched chains that construct the rest of the structure of the material.

The team took two approaches to create a polymer that triggers an immune response when embedded in living tissue. Both incorporated the compound selenophen into the backbone, and other immunomodulatory materials were added to the side chains.

“We have developed these new materials based on these two strategies. These new materials not only show excellent biocompatibility, but also maintain the good electrical performance required for bioelectronic devices,” said co-authors and PhD in Molecular Engineering. Student Zhichang Liu.

In mouse testing, the team, including Read’s first author, Dr. Nan Lee, is seen as a 68% reduction in collagen density, that is, scar tissue built around pacemakers and other devices, which reduces efficiency over time.

To address the epic challenges of foreign body reactions in embedded devices, this study complements the hydrogel semiconductors created by Wang Research Group, which was created last year, to improve the bodies and machines.

Semiconductor studies of hydrogels have altered the physical structure of embedded devices, but this new work changes chemistry and therefore does not trigger a large immune response.

“Overall, this comes from our goal of dealing with the epic challenges that are universally existing challenges for all kinds of embedded devices,” Wang said. “When foreign objects are inserted into the human body, the immune system begins to attack it. First, this produces side effects for the patient. Second, it also affects the long-term stability of the device.”

This means that over time devices that regulate heartbeat, record brain signals, take important measurements, and release insulin and other drugs become less efficient and in some cases completely stop working.

“To be recorded effectively, biological signals are needed so that they can travel efficiently from organs to devices,” Wang said. “However, the foreign body reaction produces a layer of dense fibrous tissue, such as scars. That scar layer insulates the device, encapsulating it to prevent efficient transport of biomolecules or other types of signals.”

Unique strengths

The team will then focus on improving the long-term stability of new materials, whilst continuing to work on ways to reduce the immune system’s response when foreign bodies are embedded, Liu said.

“During this study, we also found several different strategies to address foreign body reactions, such as the reduction in reactive oxygen species,” she said. “It’s also part of this very important study.”

For Wang, the ability to better connect electronic devices with the human body reflects the greater interface: the relationship between materials science and immunology. He praised the interdisciplinary approach of schools, organized by research topics rather than university faculties, to thrive creative breakthroughs.

“This is one of the unique strengths of Uchicago Pritzker Molecular Engineering,” Wang said. “What new technology frontiers can these two research spaces, these two fields begin interaction at a deep level?”