Tag Archives: soft electrodes

Connecting nerves to electronics with soft gold

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Gold nanowires that are tissue-like? That’s how this nanogold composite is described in a research paper from researchers at Linköping University (Sweden). Before getting to a link and citation for the paper, here’s an announcement about the work in an August 6, 2024 news item on ScienceDaily,

Gold does not readily lend itself to being turned into long, thin threads. But researchers at Linköping University in Sweden have now managed to create gold nanowires and develop soft electrodes that can be connected to the nervous system. The electrodes are soft as nerves, stretchable and electrically conductive, and are projected to last for a long time in the body.

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An August 6, 2024 Linköping University press release (also on EurekAlert), which originated the news item, provides context for the research,

Some people have a “heart of gold”, so why not “nerves of gold”? In the future, it may be possible to use this precious metal in soft interfaces to connect electronics to the nervous system for medical purposes. Such technology could be used to alleviate conditions such as epilepsy, Parkinson’s disease, paralysis or chronic pain. However, creating an interface where electronics can meet the brain or other parts of the nervous system poses special challenges.

“The classical conductors used in electronics are metals, which are very hard and rigid. The mechanical properties of the nervous system are more reminiscent of soft jelly. In order to get an accurate signal transmission, we need to get very close to the nerve fibres in question, but as the body is constantly in motion, achieving close contact between something that is hard and something that is soft and fragile becomes a problem”, says Klas Tybrandt, professor of materials science at the Laboratory of Organic Electronics at Linköping University, who led the research.

Researchers therefore want to create electrodes that have good conductivity as well as mechanical properties similar to the softness of the body. In recent years, several studies have shown that soft electrodes do not damage the tissue as much as hard electrodes may do. In the current study, published in the journal Small, a group of researchers at Linköping University have developed gold nanowires – a thousand times thinner than a hair – and embedded them in an elastic material to create soft microelectrodes.

“We’ve succeeded in making a new, better nanomaterial from gold nanowires in combination with a very soft silicone rubber. Getting these to work together has resulted in a conductor that has high electrical conductivity, is very soft and made of biocompatible materials that function with the body,” says Klas Tybrandt.

Silicone rubber is used in medical implants, such as breast implants. The soft electrodes also include gold and platinum, metals that are common in medical devices for clinical use. 
However, making long, narrow gold nanostructures is very difficult. This has so far been a major obstacle, but the researchers have now come up with a new way to manufacture gold nanowires. And they do it by using silver nanowires.

As silver has unique properties that make it a very good material to create the kind of nanowires that the researchers are after, it is used in some stretchable nanomaterials. The problem with silver is that it is chemically reactive. In the same way that silver cutlery will discolour over time when chemical reactions occur on the surface, silver in nanowires breaks down so that silver ions leak out. In a high enough concentration, silver ions can be toxic to us.

It was when Laura Seufert, a doctoral student in Klas Tybrandt’s research group, was working on finding a way to synthesize, or “grow”, gold nanowires that she came up with a new approach that opened up new possibilities. At first, it was difficult to control the shape of the nanowires. But then she discovered a way that resulted in very smooth wires. Instead of trying to grow gold nanowires from the beginning, she started with a thin nanowire made of pure silver.

“As it’s possible to make silver nanowires, we take advantage of this and use the silver nanowire as a kind of template on which we grow gold. The next step in the process is to remove the silver. Once that’s done, we have a material that has over 99 per cent gold in it. So it’s a bit of a trick to get around the problem of making long narrow gold nanostructures,” says Klas Tybrandt.

In collaboration with Professor Simon Farnebo at the Department of Biomedical and Clinical Sciences at Linköping University, the researchers behind the study have shown that the soft and elastic microelectrodes can stimulate a rat nerve as well capture signals from the nerve. 

In applications where the soft electronics are to be embedded in the body, the material must last for a long time, preferably for life. The researchers have tested the stability of the new material and concluded that it will last for at least three years, which is better than many of the nanomaterials developed so far.

The research team is now working on refining the material and creating different types of electrodes that are even smaller and can come into closer contact with nerve cells.

The research has been funded with support from, among others, the Swedish Foundation for Strategic Research, the Swedish Research Council, the Knut and Alice Wallenberg Foundation and through the Swedish Government’s strategic research area in advanced functional materials, AFM, at Linköping University.

Here’s a link to and a citation for the paper,

Stretchable Tissue-Like Gold Nanowire Composites with Long-Term Stability for Neural Interfaces by Laura Seufert, Mohammed Elmahmoudy, Charlotte Theunis, Samuel Lienemann, Yuyang Li, Mohsen Mohammadi, Ulrika Boda, Alejandro Carnicer-Lombarte, Renee Kroon, Per O.Å. Persson, Aiman Rahmanudin, Mary J. Donahue, Simon Farnebo, Klas Tybrandt. Small DOI: https://doi.org/10.1002/smll.202402214 First published: 30 June 2024

This paper is open access.

Printing jello and conducting electricity

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The July 4, 2012 news item on ScienceDaily about a gel that behaves like biological tissue but conducts electricity is another one of those pieces of research which illustrate the idea that the boundary between the behaviour of biological and nonbiological materials is wavering,

The material, created by Stanford chemical engineering Associate Professor Zhenan Bao, materials science and engineering Associate Professor Yi Cui and members of their labs, is a kind of conducting hydrogel — a jelly that feels and behaves like biological tissues, but conducts electricity like a metal or semiconductor.

That combination of characteristics holds enormous promise for biological sensors and futuristic energy storage devices, but has proven difficult to manufacture until now.

The ScienceDaily news item originated in a June 27, 2012 article written by Max McClure for the (University of) Stanford Report,

Bao and Cui made the gel by binding long chains of the organic compound aniline together with phytic acid, found naturally in plant tissues. The acid is able to grab up to six polymer chains at once, making for an extensively cross-linked network.

“There are already commercially available conducting polymers,” said Bao, “but they all form a uniform film without any nanostructures.”

In contrast, the new gel’s cross-linking makes for a complex, sponge-like structure.  The hydrogel is marked with innumerable tiny pores that expand the gel’s surface area, increasing the amount of charge it can hold, its ability to sense chemicals, and the rapidity of its electrical response.

Still, the gel can be easily manipulated. Because the material doesn’t solidify until the last step of its synthesis, it can be printed or sprayed as a liquid and turned into a gel after it’s already in place – meaning that manufacturers should be able to construct intricately patterned electrodes at low cost.

Here’s more about the electrical conductance properties from the McClure article,

The material’s unusual structure also gives the gel what Cui referred to as “remarkable electronic properties.”

Most hydrogels are tied together by a large number of insulating molecules, reducing the material’s overall ability to pass electrical current. But phytic acid is a “small-molecule dopant” – meaning that when it links polymer chains, it also lends them charge. This effect makes the hydrogel highly conductive.

The gel’s conductance is “among the best you can get through this kind of process,” said Cui. Its capacity to hold charge is very high, and its response to applied charge is unusually fast.

The substance’s similarity to biological tissues, its large surface area and its electrical capabilities make it well suited for allowing biological systems to communicate with technological hardware.

The researchers envision it being used in everything from medical probes and laboratory biological sensors to biofuel cells and high-energy density capacitors.

“And all it’s made of are commercially available ingredients thrown into a water solution,” said Bao.

The July 4, 2012 ScienceDaily news item provided this citation for the paper,

L. Pan, G. Yu, D. Zhai, H. R. Lee, W. Zhao, N. Liu, H. Wang, B. C.- K. Tee, Y. Shi, Y. Cui, Z. Bao. Hierarchical nanostructured conducting polymer hydrogel with high electrochemical activity. Proceedings of the National Academy of Sciences, 2012; 109 (24): 9287 DOI: 10.1073/pnas.1202636109