Specialized polymers bring us one step closer to 'cyborgs'

A new discovery makes it easier to connect electronics into human tissues.

Our squishy, salty brains are capable of doing incredible things — from commanding us to walk to solving complex questions about our world. Scientists and science-fiction authors alike have yearned to understand (and even) control our brains, but they've thus far been an incredibly complex nut to crack.

Intriguingly, the development of a new, biocompatible polymer coating for electronic implants by a team of researchers at the University of Delaware could be the key to better understanding this biological black box.

These polymers would not only leave less scarring on biological tissue than inorganic-coated electronics but would also allow scientists to fine-tune the sensitivities of polymers — which could allow for the creation of early warning systems for the presence of harmful diseases.

Furthermore, as these devices continue to mature, scientists say they could be the answer to creating an effective human brain-A.I. interface in the future.

The study's lead author and professor of biomedical engineering at the University of Delaware, David Martin, tells Inverse that current technology is being used to develop biocompatible electronics such as pacemakers, cochlear implants, and deep brain-stimulations. Critically, these technologies have faced limitations — Martin says his team's innovation could be the fix.

"There are limitations both in the reliability and performance of the devices themselves," Martin says. "Our materials are intended to bridge the gap between the inert, rigid, solid, abiotic engineered device and the living, soft, wet, biotic tissue."

The material scientists and engineers behind this research presented their findings Monday at the American Chemical Society's (ACS) Fall 2020 Virtual Meeting & Expo. The team stumbled across this need for a better, biocompatible interface when running into trouble integrating inorganic electronics into the brain.

The search for biocompatible coating — Typical microelectronic materials, like silicon, gold, stainless steel, or iridium, can cause scarring when integrated into biological tissue. In the case of the brain or muscle tissue, this scarring can disrupt the movement of electrical signals.

Instead of doing away with these materials altogether, Martin and colleagues hypothesized that designing a biocompatible coating to go over these devices might give them the best of both worlds.

After experimenting on a number of materials, the team came across an unlikely hero.

"We started looking at organic electronic materials like conjugated polymers that were being used in non-biological devices," Martin explains. "We found a chemically stable example that was sold commercially as an antistatic coating for electronic displays."

The polymer coating is technically called poly(3,4-ethylenedioxythiophene), or PEDOT. It is both electrically and ionically active, which the authors explain helps lower its impedance (aka its opposition to flowing electric charge) by three to four orders of magnitude compared to electronics without this coating.

"The ability to do the polymerization in a controlled way inside a living organism would be fascinating."

Thanks to its low impedance, this coating increases both the signal strength and battery life of these devices.

In addition to these basic improvements, the authors say that these polymers can also be tweaked to add specific functional properties. Researchers can effectively add any peptides, antibodies, or even DNA they want to these modified PEDOTs, Martin explains.

"Name your favorite biomolecule, and you can in principle make a PEDOT film that has whatever biofunctional group you might be interested in," he says.

Martin and his colleagues tested out this property by incorporating into the film an antibody capable of detecting when a particular blood vessel growth hormone is hijacked by a tumor.

What's next — A feature like this could be used to detect the early stages of certain cancers. Martin says his research team has been pursuing this kind of functionality for the past twenty years.

Beyond its diagnostic use, Martin tells Inverse there's also interest in how a polymer coating like this could be used in brain-machine interfaces and even in the incorporation of A.I. into the human brain. While futuristic, Terminator-like cyborgs are still within the realm of science fiction, Martin says this field of research is rapidly evolving.

"In real life, we have already seen paralyzed people able to control cursors on a computer screen and prosthetic arms with their brains," Martin says. "Recently there have been a number of big players like Glaxo Smith Kline and Elon Musk’s Neuralink get into the game; the technology is now rapidly evolving and it is clear there are going to be some remarkable future developments."

As for this research, Martin says that their next steps will be to better understand how to tune the behavior of these polymers and then (eventually) to incorporate them into living organisms.

"The ability to do the polymerization in a controlled way inside a living organism would be fascinating."

Abstract: We have been investigating the design, synthesis, and characterization of conjugated polymers for integrating bioelectronic devices with living tissue. These devices are under development for a variety of applications that require long term electrical communication and interfacing between electronically active engineered devices and soft electrolytic biological systems. Specific examples including microfabricated neural electrodes, bionic prosthetics, and cardiac mapping devices. We have developed a variety of functionalized poly(alkoxythiophenes) that make it possible to significantly improve the electronic, mechanical, and biological properties of these materials. We will discuss the use of electrochemical deposition methods, combined with a variety of physical and characterization techniques, that have enabled us to understand the relationship between chemical structure, morphology, and macroscopic properties of these polymers. These studies have inspired the design new molecular structures for improved performance. Most recently we have been directly monitoring the electrodeposition process using low dose liquid cell transmission electron microscopy.
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