A Touch of Silver

The comments below are an edited and abridged synopsis of an article by Lisa Kulick

In the field of robotics, metals offer advantages: strength, durability and electrical conductivity. But they are heavy and rigid—properties undesirable in soft and flexible systems for wearable computing and human-machine interfaces.

A Touch of Silver | BullionBuzz | Nick's Top Six
Silver gears and printed circuit board with copy space. Concept idea

Hydrogels, however, are lightweight, stretchable and biocompatible, making them excellent materials for contact lenses and tissue engineering scaffolding. They are poor at conducting electricity, which is needed for digital circuits and bioelectronics applications.

Researchers at Carnegie Mellon University have developed a unique silver-hydrogel composite that has high electrical conductivity and is capable of delivering direct current while maintaining soft compliance and deformability.

The research team suspended tiny silver flakes in a polyacrylamide-alginate hydrogel matrix. After going through a partial dehydration process, the flakes formed percolating networks that were electrically conductive and robust to mechanical deformations. By manipulating this dehydration and hydration process, the flakes can be made to stick together or break apart, forming reversible electrical connections.

The silver-hydrogel composite can be printed by standard methods like stencil lithography, similar to screen printing. The researchers used this technique to develop skin-mounted electrodes for neuromuscular electrical stimulation. The composite could cover a large area of the human body, like a second layer of nervous tissue over skin.

Future applications could include treating muscular disorders and motor disabilities, such as assisting someone with tremors from Parkinson’s disease or difficulty grasping something with their fingers after a stroke.

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