“The spinal cord is a challenging structure to interface with,” explains team leader Polina Anikeeva of the Massachusetts Institute of Technology (MIT). “It experiences strains of up to 12% and can be damaged easily. In our work, we have applied a thermal drawing process traditionally used in the optical fibre industry to elastomers to create a stretchable fibre that can be implanted in a mouse’s spinal cord.”

Until now, such optical waveguides were made from brittle materials, which are not suitable for implanting in the spinal cord, adds team member and lead author of the study Alice Lu, also of MIT. “Our flexible and stretchable system can move within the spinal cord and causes minimal damage.”

The researchers coated their fibres with micron-thick meshes of conductive silver nanowires to be able to measure electrical signals from neurons. In mice that had genetically modified light-responsive neurons, the probes were able to simultaneously record neuronal activity and produce hind-limb contractions when the lower region of their spinal cords was illuminated with laser light, which stimulated neural activity.

And that is not all. The devices can accurately monitor electrical signals even when the mice are moving around freely. Being able to do this has been difficult until now because electrical signals from neurons can become mixed up with those from breathing and heartbeats, for example, and conventional probes are not able to connect to the specific neurons involved.

“We hope that our probes will allow for studies of spinal cords in animal models of neurological and neuromuscular disorders,” Anikeeva tells nanotechweb.org. “They may also help elucidate the neuronal pathways contributing to recovery following spinal-cord injury.

The team, which includes researchers from the University of Washington (UW), the University of Oxford in the UK and Advanced Functional Fabrics of America Inc., says that it is now trying to make the nanofibres more biocompatible and chemically stable. “Together with our colleagues from the Center for Sensorimotor Neural Engineering at UW, we aim to use these probes to study neural plasticity in the spinal cord following traumatic injury,” adds Lu. “We will also work with neuroscientists to study specific neural circuits and adapt the probe so that it can tune in on multiple neuronal channels by increasing the number of recording channels per probe.”

The research is detailed in Science Advances DOI: 10.1126/sciadv.1600955.