A stretchy, conductive type of plastic could help power the next generation of implantable biomedical devices, like longer-lasting pacemakers or glucose monitors, according to Enrique Gomez, professor of chemical engineering at Penn State.
Using advanced imaging technology to examine a stretchy material commonly used in soft robotics and touchscreens known as PEDOT:PSS, Gomez and his team found that adding different salt additives and water enabled the material to grow hair-like fibers capable of effectively conducting electricity. According to the researchers, who recently published their findings in Nature Communications, minor changes to the plastic can have a major impact on the material's physical properties and conductivity.
One of the primary challenges facing the development of bio-friendly devices is balancing the different ways computers and the human body move electrical currents, Gomez explained. Although both the body and computers conduct electricity, they do so differently.
"Our nerves and neurons move electricity around our body using ionic currents, which are essentially circuits built out of mixtures of salt and ions in the body," said Gomez, who also serves as associate dean for equity and inclusion in the Penn State College of Engineering. "Computers conduct electricity by moving electrons through metal wires and silicon semiconductors. PEDOT:PSS is a remarkable material in that it can conduct electrons, while at the same time remaining sensitive to the existing ion currents in the body."
Despite its usefulness, researchers don't fully understand how the material works, according to Gomez. To learn more, his team used a highly advanced microscope technology, known as cryogenic electron microscopy, or cryo-EM, to examine the gel-like plastic. Unlike traditional microscopes, which focus light through lenses to magnify an image, cryo-EM microscopes use the flow of electrons to examine materials at some of the highest resolutions possible.
"These are some of the most advanced microscopes in the world, as they can be used to image things like viruses, proteins and polymers, which we specialize in at Penn State," Gomez said. "We are experiencing a revolution in microscopy, as these machines allow us to image materials at incredibly high levels of detail."
The team placed a small droplet of the material encased in a thin, nanoscopic film, only a fraction of the width of a human hair. They repeated this process several times, making minor adjustments to each sample's chemical makeup by adding different types of salt. They then plunged the samples into liquid ethane kept at -180 degrees Celsius (C) - slightly warmer than the surface of the moon at night. This is to ensure the material samples don't burn up in the high temperatures produced by the electrons, and allows the team to examine how different salt additives impact ion and electron transfer in the material.
