Mesh electronics is a submicron thickness, large-area macroporous network, explains team leader Charles Lieber. The meshes are fabricated as flat 2D sheets using standard semiconductor lithography techniques and are normally suspended (like a colloid) in aqueous solution. “In our specific design, they are rolled up into a tubular, scroll-like structure and drawn into a syringe needle.”

“We can now deliver these structures into specific brain regions with a spatial precision of 20 microns (which is on the scale of a single neuron),” he told nanotechweb.org. “This is thanks to the controlled injection approach we have developed, where we are able to control the rate at which we retract the needle. This means that the mesh structure remains fully extended in the dense tissue of the brain during injection and does not crumple.”

A million times more flexible

Lieber and colleagues’ idea to electrically bond the mesh electronics with conductive printed ink (containing carbon nanotubes) allows the mesh to be connected to a flexible flat cable that acts as a “plug-in” interface for measurement devices that are directly able to monitor brain activity.

“The main advantages of our mesh electronics are its ultraflexibility and open structure, which allows it to seamlessly penetrate endogenous biological tissue, like 3D networks of neurons in the brain, for the first time,” says Lieber. “Our structures are roughly a million times more flexible than traditional flexible electronics (they have a bending stiffness of 0.086 versus 0.16–1.3 × 104 nN·m). This also means they can be injected through a standard syringe without being damaged.”

The injectable electronics can be used to monitor a broad range of brain activity, from low-frequency local field potentials to high-frequency single-unit “spikes”, and this in precisely targeted functional regions and/or layers of the brain, he adds. Indeed, the team says that it has already injected the meshes into live mice and monitored their brain activity for periods of more than six months. “This capability is unprecedented,” states Lieber, “and will ultimately allow for long-term monitoring of brain activity and even for functional stimulation in deep regions of the brain implicated in diseases like Parkinson’s, for example, in a manner simply not possible before.”

The electronics might also be injected into other parts of the body, like the retina or the spinal cord. Again, the researchers have already succeeded in doing this in live mice and taking electronic recordings in vivo.

“Ultimately, our technique could help us to discover how the brain functions and repairs itself on a fundamental level,” says Lieber. “It will also allow us to study various brain-related diseases, like stroke and Alzheimer’s.”

The research is detailed in Nano Letters DOI: 10.1021/acs.nanolett.5b02987.