Fabrication of Flat-Interface Nerve Electrodes for Recording Neural Activity

Start with a flat nerve-wrapping electrode placed on a silicone sheet, a transparency sheet, and a guiding sketch.

This setup contains reference and recording contacts connected by fine insulated wires, spacers, and suturing holes.

Place a shielding metal on the polymer layer covering the electrode to block unwanted signals from surrounding nerves.

Apply a polymer to attach the metal piece and let it solidify.

Attach protective adhesive tape and layer a polymer over the shielding metal.

Place a plastic layer on top and press to flatten it.

After solidifying, remove the excess polymer and the tape.

Expose the spacer and cut the polymer around the electrode.

Trim the excess polymer on the wire.

Cut the polymer covering the shielding metal.

Detach the electrode from the base layers using a thread.

Flip it and cut the polymer over the center and reference contacts to expose the recording surface.

Finally, wrap the electrode around the nerve to record signals.

To add a shielding layer, remove the large fixture bar, and remove the transparency piece with tweezers. Then, place the shielding sheet in the center of each face of the electrode and gently press it into the electrode.

Then, deposit some uncured silicone into the through-holes, and partially cure it for 30 minutes at 130 degrees Celsius. Once cooled to room temperature, place adhesive tape over the outer ends of the electrode and over the closing flanges, to keep silicone out of these segments.

Then, repeat the process of adding a layer of silicone to cover the entire electrode body. Follow this by placing silicone and transparency sheets over the electrode, and then, secure them with a large fixture bar and cure the silicone.

After curing, to complete the process, remove the excess silicone and the tape. Then, cut windows through the silicone to expose the spacer segments, and use tweezers to remove the spacer segments.

Next, under a microscope, remove the tape and silicone over the tubes, until it is level with the electrode body. Then, carefully cut around the perimeter of the electrode down to the base plate.

Now, taking caution to not damage the electrode, follow the guide diagram to shape the leads' exit sites. Cut out a triangle between each tube pair that goes completely through the electrode layers, and onto the outer side.

Now, cut windows into the silicone that covers the shielding layer. Then, glide the polypropylene suture between the electrode base and the adjacent transparent layer, and use it to delaminate the nearly finished cuff electrode. Finally, cut windows out of the silicone to expose the center contacts and reference contacts.

The fabricated fine electrode was used to record the activity of the sciatic nerve in a dog over 7.5 months. A customized preamplifier and a super beta input instrumentation amplifier were implemented. The electrode was implanted around the nerve by suturing the two free edges together. The cuff flattens the nerve while retaining flexibility in the longitudinal direction.