A biocompatible and stretchable transistor for implantable devices

Recent technological advances have opened new possibilities for the development of advanced biomedical devices that could be implanted inside the human body. These devices could be used to monitor biological signals that offer insight about the evolution of specific medical conditions or could even help to alter problematic physiological processes.

Despite their potential for the diagnosis and treatment of some conditions, most implantable devices developed to date are based on rigid electronic components. These components can damage tissue inside the body or cause inflammation.

Some electronics engineers have been trying to develop alternative implantable electronics that are based on soft and stretchable materials, such as polymers. However, most known polymers and elastic materials are not biocompatible, which means that they can provoke immune responses and adversely affect the growth of cells.

Researchers at Kyung Hee University, Sungkyunkwan University and other institutes in South Korea have introduced a new organic transistor, a device that modulates the flow of electrical current in circuits, which appears to be both stretchable and biocompatible.

Their device, introduced in a paper in Nature Electronics, was made using a blend of extremely thin semiconducting fibers and a biocompatible composite elastic material.

“For more than a decade, our group has been working on intrinsically stretchable semiconductors that can elongate like human skin while still functioning as transistors,” Jin Young Oh, senior author of the paper, told Tech Xplore.

“While we made progress in mechanical stretchability, one critical limitation remained: most elastomers used in research were industrial grade, lacking true biocompatibility for safe long-term implantation. This challenge inspired us to rethink materials at a fundamental level.”

The researchers involved in the development of the new transistor have been exploring the use of organic semiconductors and medical elastomers for the development of biomedical devices for some time now.

Building on their earlier work, they tried to realize the first transistor that is stretchable, but that can also be safely inserted inside the body without causing inflammation or damaging tissue.

“Our transistor is built from a composite of a high-performance semiconducting polymer (DPPT-TT) and a medical-grade rubber called brominated isobutylene–isoprene rubber (BIIR),” explained Oh.

“Using a vulcanization process which is a classical rubber crosslinking method, we created a nanofiber network of semiconductors embedded in an elastic, biocompatible matrix. This architecture provides both stable charge transport and exceptional mechanical softness.”

The researchers designed dual-layer electrodes for their device that are made of silver and gold, two materials that are conductive, chemically stable and would not become corroded when placed in bodily fluids for prolonged periods of time.

In initial tests, they found that their transistor could stretch up to 50% strain, successfully enduring 10,000 cycles of stretching while still operating normally.

Oh and his colleagues also implanted their device under the skin of mice, to assess its performance and safety in biological environments. They found that the transistor performed remarkably well, while also conforming to the animals’ tissue and resisting degradation when in contact with biological fluids.

“We showed not only stable device operation under physiological conditions but also excellent in vitro and in vivo safety, with no inflammation or fibrotic encapsulation after 30 days of implantation,” said Oh. “We further validated logic gates and active-matrix arrays, proving the scalability of the platform.”

The soft and biocompatible transistor developed by this team of researchers could soon be used to develop a wide range of electronics. These include biosensors that can monitor physiological processes, smart implants for the precise delivery of drugs, prosthetic systems that connect the brain with robotic limbs and even new types of consumer devices.

“Our next studies will follow two distinct directions,” said Oh. “On the hardware side, we aim to further improve transistor performance, scalability, and integration into complex circuits such as logic-in-memory architectures. On the biomedical side, we plan extended in vivo studies to validate long-term safety and reliability.”

Eventually, Oh and his colleagues would also like to explore the possibility of using their transistor to create implantable brain-inspired devices. For example, they envision new energy-efficient and AI-powered systems that could sense the environment inside the body, while also making predictions based on the data they collect.

“Ultimately, we envision combining hardware advances with AI-driven software to create self-learning implantable electronics,” added Oh.

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