The scientific community has long been fascinated by the ability to soften. Bioelectronics devices, but hurdles have been encountered in identifying materials that are biocompatible and possess all the necessary properties to function effectively.

Researchers have now taken a step in the right direction in bioelectronics, modifying existing biocompatible materials so that they can efficiently conduct electricity in wet environments and send and receive ionic signals from biological media.

Neural pathways - ideal picture.Neural pathways - ideal picture.

Neural pathways – ideal picture. Image credit: Pixabay (Free Pixabay License)

“We’re talking about an order-of-magnitude improvement in the ability of soft bioelectronic materials to function efficiently in a biological environment,” said Iram Amasian, co-author of a paper on the work and professor of materials science and engineering. She says at North Carolina State University. “This is not an incremental development.”

There is great interest in fabricating organic bioelectronics and organic electrochemical transistors (OECTs), which have a wide range of biomedical applications. However, a limiting factor is identifying non-toxic materials that can conduct electricity, interact with ions—important for functioning in biological environments, and effective in the aqueous, water-based environment of biological systems. can work properly.

One material of interest is PEDOT:PSS, a non-toxic polymer capable of conducting electricity. PEDOT:PSS is used to form thin films that are effectively fiber networks that are only nanometers wide. An electrical current can flow through the fibers, which are also sensitive to the ions in their environment.

“The idea is that, because the ions interact with the fibers – and affect their conductivity – PEDOT:PSS can be used to understand what is happening around the fibers,” Laine Taussig said. , says the paper’s co-first author and recent Ph.D. D is a graduate of NC State who now works at the Air Force Research Laboratory.

Basically, PEDOT:PSS will be able to monitor its biological environment. But we can also use an electrical current to affect the ions around the PEDOT:PSS, sending signals to the biological environment,” says Masood Ghasemi, co-first author and a former postdoctoral fellow at NC State. Fellows who are now postdoctoral fellows at Penn.

However, the structural stability of PEDOT:PSS decreases significantly when placed in aqueous environments – such as biological systems. This is because PEDOT:PSS is a single material made of two components: PEDOT, which conducts electricity and is insoluble in water; and PSS, which responds to ions, but is soluble in water. In other words, PSS material starts to break down when it comes in contact with water.

Previous attempts to stabilize the structure of PEDOT:PSS have been successful in helping the material withstand aqueous environments, but have compromised both the performance of PEDOT:PSS as a conductor and the PSS component of the material for ions. It has made it more difficult to interact with.

“Our work here is important, because we have discovered a new way to make PEDOT:PSS that is structurally stable in a wet environment and able to interact with ions and conduct electricity very efficiently,” George says Maliaras, co-corresponding author. and Prince Philip, Professor of Technology at Cambridge University.

Specifically, researchers start with PEDOT:PSS in solution and then add ionic salts. Given time, the ionic salts interact with PEDOT:PSS, causing it to self-assemble into fibers with a unique structure that is stable in wet environments. This modified PEDOT:PSS is then dried and the ionic salts are washed away.

“We already knew that ionic salts can affect PEDOT:PSS,” says Amasian. “What’s new here is that by giving the ionic salts more time to see the full range of these effects, we modified the crystalline structures of PEDOT and PSS to self-assemble on a molecular scale. This makes PSS impermeable to water in the environment, allowing PEDOT:PSS to maintain its structural stability at the molecular level.

“This change is also hierarchical, meaning that changes occur at the molecular level down to the macroscale,” says Yaroslava Yingling, co-author of the paper and Kobe Steel Distinguished Professor of Materials Science and Engineering at NC State. “Ionic salts cause PEDOT:PSS to predominantly reorganize itself into a phase resembling a web-like gel that is stable in both dry and wet environments.”

In addition to being stable in aqueous environments, the resulting films retain their conductivity. What’s more, because PEDOT and PSS are strongly bonded, it is easier for ions to reach and interact with the PSS component of the material.

“This new phase of PEDOT:PSS was used by our colleagues at Cambridge to make OECTs,” says Amassian. “And those OECTs set a new state-of-the-art standard in both volumetric capacitance and electronic carrier mobility. In other words, they are the new gold standard in both conductivity and ion response in biofriendly electronics.

“Given that PEDOT:PSS is transparent, flexible, expandable, conductive and biocompatible, the range of potential applications is exciting – extending well beyond the biomedical sector,” said Enrique Gomez, co-corresponding author and Penn State Says the professor.

paper,”Electrostatic self-assembly produces a structurally stable PEDOT:PSS with efficient mixed transport and high performance OECTs.Published in the journal. Case. This paper was co-authored by Albert Kwansa, Assistant Research Professor of Materials Science and Engineering at NC State. Nathan Woodward, Ph.D. student at NC State; Single Hahn and Scott Kenny of Cambridge; and Ruipeng Lee of Brookhaven National Laboratory.

The authors: Laine Taussig, Nathan Woodward, Albert L. Kwansa, Yaroslava G. Yingling and Aram Amassian, North Carolina State University; Masoud Ghasemi, North Carolina State University and Pennsylvania State University; Singal Hahn, Scott T. Kane and George G. Milliars, University of Cambridge; Ruipeng Li, Brookhaven National Laboratory; and Enrique de Gomez, Pennsylvania State University

Published: January 16, Case

DOI: 10.1016/j.matt.2023.12.02

This work was supported by the Office of Naval Research under grants N00014-23-1-2001 and N00014-19-1-2453.

Source: NCSU