Injectable Mesh Electronics for Stable Single-Neuron Recordings in a Mouse Brain

To inject mesh electronics into a mouse brain, use a dental drill and stereotaxic frame to open a craniotomy at the desired coordinates on the skull. Open a second craniotomy away from the injection site for the insertion of a stainless steel grounding screw, or wire.

Then, fix a clamping substrate to the skull with dental cement. An approximately 1-millimeter wide cut in the substrate improves the reliability of the folding step later in the procedure. Afterward, mount the pipette holder with the needle containing mesh electronics into the stereotaxic frame using a right-angle end clamp. Attach the side outlet of the pipette holder to a 5-milliliter syringe fastened in a syringe pump with a 0.5 to 1-meter-long capillary tubing.

Then, use the stereotactic frame to position the tip of the needle at the desired starting location within the brain. Position the camera to display the top of the mesh electronics probe within the glass needle. Initiate the flow by setting the syringe pump to a low speed and pressing Start.

Slowly increase the flow rate if the mesh electronics probe does not move within the needle. As the mesh electronics probe starts to move within the needle, use the stereotactic frame to retract the needle at the same rate as which the mesh electronics probe is being injected, using the marked original position of mesh electronics as a guide.

Continue flowing saline, and retracting the needle until the needle has exited the skull. Then, stop the flow from the syringe pump. In this procedure, use the stereotactic frame to carefully guide the needle to the flat, flexible cable clamping substrate and across the gap, flowing the solution with the syringe pump to generate a slack in the mesh electronics interconnects.

Once the needle is above the clamping substrate and across the gap, resume the flow at a faster rate to eject the mesh electronics input/output pads onto the clamping substrate. Using tweezers in a pipette of deionized water, bend the input/output pads to 90-degree angle as close to the first input/output pad as possible.

Once the input/output pads are aligned, unfolded, and at a 90-degree angle to the mesh stem, dry them in place with gently flowing compressed air. Cut the clamping substrate at a straight edge approximately 0.5 to 1 millimeter from the edge of the input/output pads.

Also, cut off extraneous parts of the clamping substrate that will hinder the insertion into the PCB-mounted 32-channel ZIF connector. Then, insert the input/output pads into the ZIF connector on the PCB and close the latch. Use measurement electronics to measure the impedance between the channels and the ground screw to confirm successful interfacing.

If the impedance values are too high, unlatch the ZIF connector, adjust the insertion, and retest until successful connection is confirmed. Subsequently, cover the ZIF connector and exposed mesh electronics interconnects with dental cement for protection. Flip the PCB at the gap in the substrate and fix the PCB with cement onto the mouse skull.

For freely moving recordings, release the mouse from the restrainer after inserting the preamplifier PCB and grounding the reference screw. Record for the desired length of time using the data acquisition system while the mouse behaves freely.