Fast-moving fluid pulls a fiber through a microfluidic device to be inserted into brain tissue. Source: Robinson Lab

A new microfluidic approach for inserting flexible, conductive carbon nanotube fibers into the brain enables monitoring of neuronal signals without damaging surrounding tissue. Rice University researchers say that their nanotube-based electrodes could help scientists discover the mechanisms behind cognitive processes and design direct interfaces to the brain that will allow patients to see, hear or control artificial limbs.

The device uses the force applied by fast-moving fluids that gently advance insulated flexible fibers into brain tissue without buckling. This delivery method may offer an alternative to the hard shuttles or stiff, biodegradable sheaths now used to deliver wires into the brain, both of which can damage sensitive tissue.

The microfluidic devices force a viscous fluid to flow around a thin fiber electrode, slowly pulling the fiber forward through a small aperture that leads to the tissue. Once it crosses into the tissue, tests showed the wire, though highly flexible, stays straight.

“The electrode is like a cooked noodle that you’re trying to put into a bowl of Jell-O,” said Rice engineer Jacob Robinson. “By itself, it doesn’t work. But if you put that noodle under running water, the water pulls the noodle straight.”

The fiber moves through an aperture about three times its size but still small enough to admit little of the fluid; none of the fluid follows the wire into brain tissue.

Once the wire is in the tissue, it’s in an elastic matrix, supported all around by the gel material,” said chemist Matteo Pasquali, a carbon nanotube fiber pioneer whose lab made a custom fiber for the project. “It’s supported laterally, so the wire can’t easily buckle.”

The researchers also devised a method to coat a carbon nanotube fiber and still keep it between 15 to 30 microns wide, well below the width of a human hair. The technology may eventually be scaled to simultaneously deliver multiple microelectrodes that are closely packed, which would make it safer and easier to embed implants.