Scientists combine silver and hydrogel to create soft bioelectronics

Researchers have developed a unique silver-hydrogel composite that is highly electrically conductive and capable of passing direct current while maintaining soft pliability and deformability. The results are published in the journal Nature Electronics.

In the field of robotics, metals have many advantages – strength, durability and electrical conductivity. But they are heavy and rigid, and these properties are not suitable for creating soft and flexible systems for wearable computers and human-machine interfaces.

On the other hand, hydrogels are lightweight, stretchable, and biocompatible, making them excellent materials for contact lens and tissue engineered frameworks. However, they do not conduct well the electricity that is needed for digital circuits and bioelectronic applications.

Researchers from the Soft Machines Laboratory at Carnegie Mellon University have created a unique silver-hydrogel composite that has high electrical conductivity and is capable of passing direct current. At the same time, it remains pliable and deformable.

The team placed micrometer-sized silver flakes in a polyacrylamide-alginate hydrogel matrix. After passing through the process of partial dehydration, the flakes formed percolation networks. They were electrically conductive and resistant to mechanical deformation. By controlling the dewatering and hydration process, the engineers caused the flakes to clump or break apart, forming reversible electrical connections.

Previous attempts to combine metals and hydrogels have resulted in a trade-off between improved electrical conductivity and reduced ductility and deformability. The engineers sought to solve this problem by drawing on their experience in developing tensile conductive liquid metal elastomers.

“With its high electrical conductivity and high elasticity, this new composite has many uses in bioelectronics and beyond,” explained Carmel Majidi, professor of mechanical engineering and author of the study. “For example, you could create a brain sticker with sensors for signal processing, a wearable device to generate power for power electronics, and stretchable displays.”

Composite silver hydrogel can be printed using standard techniques such as screen lithography. It is similar to screen printing. Researchers have used this technique to develop dermal electrodes for electrical neuromuscular stimulation. According to Majidi, the composite can cover a large area of ​​the human body, “like the second layer of nerve tissue on the skin.”

In the future, the composite will be useful in the treatment of muscle disorders and movement disorders, for example, in patients with Parkinson’s disease or after a stroke.

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Alexandr Ivanov earned his Licentiate Engineer in Systems and Computer Engineering from the Free International University of Moldova. Since 2013, Alexandr has been working as a freelance web programmer.
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Alexandr Ivanov

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