“I wanted to create a multimodal interface with mechanical properties compatible with tissues, for neural stimulation and recording,” as a tool for better understanding spinal cord functions, said MIT researcher, Chi (Alice) Lu.
The obvious starting point was some kind of elastomer, but most of are not adaptable to the process of ‘fibre drawing’, which turns a relatively large bundle of materials into a thread that can be narrower than a hair.
“You can match the stretchiness with a rubber, but drawing it is difficult — most of them just melt,” said fellow researcher Professor Polina Anikeeva.
The team combined a newly developed transparent elastomer, which could act as a waveguide for optical signals, and a coating formed of a mesh of silver nanowires, to produce a conductive layer for the electrical signals.
To process the transparent elastomer, the material was embedded in a polymer cladding that enabled it to be drawn into a fibre that proved to be highly stretchable as well as flexible. The cladding is dissolved away after the drawing process. After the entire fabrication process, what’s left is the transparent fibre with electrically conductive, stretchy nanowire coatings. The fibre can stretch by at least 20 to 30% without affecting its properties.
“It’s really just a piece of rubber, but conductive,” said Professor Anikeeva. “We’re the first to develop something that enables simultaneous electrical recording and optical stimulation in the spinal cords of freely moving mice.
“Eventually, we’d like to be able to use something like this to combat spinal cord injury. But first, we have to have biocompatibility and to be able to withstand the stresses in the spinal cord without causing any damage.”
