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| Vidhika Damani and assistant professor Laure Kayser inspect a sample of the reversible conductive hydrogel they developed for bioelectronics applications. Photo Credit: Evan Krape |
What if a doctor could inject an electricity-conducting liquid into the body, let it temporarily solidify to record nerve signals or jump-start healing, and then return it to liquid form for easy removal?
That vision is edging closer to reality. University of Delaware researchers have developed a reversible conductive hydrogel, a material that can alternate between liquid and gel states. The hydrogel is designed to serve as an interface between conventional electronics and the body’s tissues, offering promise for both injectable implants and wearable devices.
The research team, led by Laure Kayser, assistant professor of materials science and engineering at UD’s College of Engineering, describes the new material in Nature Communications.
The material’s reversible nature provides a unique advantage over conventional conductive hydrogels, which can be challenging to insert and remove from the body. The new material shifts from liquid to gel at 35 degrees Celsius, just below body temperature (37° C). That means it could be injected or applied as a liquid, solidify on contact with warm tissue to take electrical readings or deliver stimulation, and be cooled and returned to liquid form for easy removal.
“Most electronic materials are metal-based and are not easily degraded by the body,” said Kayser, who holds a joint appointment in the Department of Chemistry and Biochemistry in the College of Arts and Sciences. “Our material is carbon-based and can be removed by simple cooling. That avoids the need for invasive surgeries to insert and remove the electronic material.”
The material also shows promise for use on irregular or uneven surfaces, such as hairy skin or scar tissue. “Pre-formed materials often don’t mold well to rough or unevenly shaped surfaces,” explained first author Vidhika Damani, who received her doctorate from UD earlier this year. “Our reversible gel could mold to any shape of choice to record an electronic signal, then simply be washed off afterward.”
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Laure Kayser looks on as Vidhika Damani prepares samples in the lab.
Photo Credit: Evan Krape
A hydrogel that reverses on command
To develop the new material, the researchers started with PEDOT:PSS, a standard conducting polymer, and PNIPAM, a heat-responsive polymer that stiffens as temperature rises. Instead of simply mixing the two polymers, the team linked them together at the molecular level, a strategy known as block copolymer synthesis. They optimized the molecular design until they achieved a material that reversibly formed stable gels that held their shape above 35° C.
The material gelled rapidly, taking about 20 to 40 seconds to convert 1 milliliter from liquid to gel. Tests showed that the material could alternate between the two phases at least 10 times while maintaining its electronic properties. Moreover, it remained stable at both room and body temperature. Even when stored as a gel for three months, the material could be re-liquified upon cooling.
To understand the material’s unique ability to transition from liquid to gel, the UD researchers collaborated with Enrique Gomez’s laboratory at the Pennsylvania State University and UD’s Darrin Pochan, Distinguished Professor of Materials Science. Extensive microscopy and scattering experiments revealed that it is the block copolymer structure that enables the reversible transition, a property that less precisely controlled or blended materials do not exhibit.
The hydrogel is also distinctive because it can carry both electronic signals and the ionic signals naturally produced by the body. Most other materials can detect only one or the other, so the new hydrogel could provide a clearer, more detailed picture of physiological activity.
Experiments in cell culture and in rat models, conducted by Kayser’s long-time collaborator Jonathan Rivnay and his team at Northwestern University, suggested that the hydrogel was well-tolerated and compatible with living tissue.
Next, the UD team attached small samples of gel to a human forearm and measured electrical output as the volunteer opened and closed a fist. “Based on the amplitude of the signal, it was 250 times better than a commercially available electrode,” said Damani, who is now a postdoctoral researcher at the University of Texas at Austin.
From gels to next-generation sensors
The future applications for the material could span from implants to wearable devices, though Damani and Kayser agree that the potential for an injectable bioelectronic is among the most intriguing possibilities.
“We're hoping this material can be used as a platform for others,” said Kayser. “We've been shipping the material to labs across the world, who are excited to try it for their own applications.”
The researchers have a U.S. patent application pending on the material, filed through UD’s Office of Economic Innovation and Partnerships, which manages intellectual property for the university.
The next step for Kayser’s lab, however, involves moving away from gels and into thin-film electronics. “We're using the same material to make very sensitive biosensors called organic electrochemical transistors,” she explained. “Because the material responds to temperature changes, these devices could act not only as sensors but also as therapeutic tools. For example, if an implanted sensor made with this material detected a rise in temperature, it could trigger the release of a drug that reduces inflammation in that area.”
From a hydrogel that flows, solidifies and flows again to future sensors that could both detect and heal, the Kayser lab’s research is helping redefine how soft materials interact with the human body. Each advance moves the vision of adaptable, reversible bioelectronics a little closer to reality.
Funding: The work was supported by the National Science Foundation’s Faculty Early Career Development (CAREER) program under award number DMR-2237888, the A
Published in journal: Nature Communications
Title: Thermo-reversible gelation of self-assembled conducting polymer colloids
Authors: Vidhika S. Damani, Xinran Xie, Rachel E. Daso, Khushboo Suman, Masoud Ghasemi, Weiran Xie, Ruiheng Wu, Yuhang Wu, Calvin L. Chao, Julian E. Alberto, Casey M. Lorch, Ai-Nin Yang, Dan My Nguyen, Tulaja Shrestha, Kayla Otero, Chun-Yuan Lo, Darrin J. Pochan, Enrique D. Gomez, Jonathan Rivnay, and Laure V. Kayser
Source/Credit: University of Delaware | Hillary Hoffman
Reference Number: ms120525_01
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