Design and Fabrication of Ultralight Weight, Adjustable Multi-electrode Probes for Electrophysiological Recordings in Mice

The overall goal of this procedure is to design and build a robust, ultra lightweight implant with independently adjustable electrodes from commercially available parts that can be customized to target any brain region and would be easily scaled for use in a variety of small animal species. First, the brain region of interest is identified and the arrangement of recording electrodes needs to be mapped out. This will determine the design of the drive body and the drive bottom.

The second step is to create the drive body to house the individual micro drives, as well as the top pieces, which will carry the electrodes using solid work software. Next, the bottom piece containing the guide tubes for the electrodes and a shielding cone are prepared. The final step is to fully assemble the hyperdrive by inserting the bottom piece into the drive body, constructing the individual micro drive, attaching the electronic interface board and loading the micro drives with electrodes.

Ultimately, the hyperdrive is implanted and single unit recordings from multiple brain regions can be obtained. Because of the ease with which the hyperdrive can be customized and scaled, it will benefit the number of researchers working in a different variety of animal models. So having robust, lightweight implants allows us to obtain a stable neuronal ensemble recordings and freely behaving mice while performing psychophysical tasks.

To begin the procedure, identify the brain region of interest. In our case, it is the lateral gent nucleus at AP coordinates negative 2.3 to negative 2.7 millimeters. The LGN is widest and this region is used to design the drive bottom.

Open the solid work software and select the front plane. Draw the 2D profile of the drive using the sketch function, which will include the contours for the drive base handles and polyamide Half slots. Ensure that the contour does not contain any open gaps.

Next, select both the front and right planes and click create axis. Then click the revolved boss base function. Select the blue 2D profile, and then revolve the 2D profile about the axis for 360 degrees.

To create the 3D drive base, click blind under direction one and input 360 degrees as the angle of rotation. After that, create one polyamide half slot by selecting the highlighted contour and using the revolve function to revolve the contour by 13 degrees about the central axis. Subsequently, select the contour for the handles and revolve it by 15 degrees about the central axis to create the second drive handle.

Using the circular pattern function in the features menu, click circular pattern and choose the central axis as the axis of revolution. Select 180 degrees as the angle and two as the number of instances, and ensure that the first handle is selected under features to pattern to create 16 polyamide half slots. Using the circular pattern function, select the first polyamide half slot as features to pattern.

Repeat the pattern 16 times by inputting 16 in the number of instances and 22.5 degrees in the angle. Define a new plane by clicking the plane tab under reference geometry. Select the two sides of one of the polyamide top slots to create a new plane.

This plane is where the receptacle will go on. Sketch the circular contours for the screw hole and polyamide hole onto this plane. For the anti torque rails, define a center line in between the two sides of the polyamide top slots.

Then draw the anti torque rails by creating two circles perpendicular to the center line who centers our one radius apart, and then trimming the middle contours to create the micro drive receptacle, including the screw hole, polyamide hole, and anti torque rail. Click on extrude boss base to create the anti torque rail and choose a blind extrude of 10 millimeters going upwards and two millimeters going downwards. Then add 0.3 millimeter fillets to the edges using the fillet function.

To further increase the strength for the screw hole and polyamide hole, click extrude, cut and choose blind. Three millimeter cuts for both going downwards and a few millimeters going upwards. Then pattern the micro drive receptacle 16 times using the center as the axis of revolution on the top of the handle.

Draw a three millimeter by three millimeter box starting at the center tip of the drive handle facing the central axis. Extrude this two millimeters upwards. Using the extrude boss function, draw circles of one millimeter diameter at the locations in which the EIB screws will go on afterward.

Make a 1.5 millimeter extrude cut to make a hole. Then pattern the box and hole twice. Using the circular pattern function, make additional extrude cuts in the drive body to further reduce the weight by drawing a pattern on the front plane and using the circular pattern function.

After that, draw a top piece sketch with the indicated dimensions in millimeters. Then use the extrude boss base to make a 3D model of it. Add one millimeter fillets to the corners using the fillet function when the drive design is complete, the drive body and top pieces may be printed through most 3D printing services.

In this procedure, lay out a small piece of double-sided tape on a flat surface and cut the 31 gauge polyamide tubes into approximately eight centimeter pieces. Next, lay out the first layer of guide tubes as close as possible to one another on the double-sided tape. Then dab a small amount of thin cyanoacrylate glue over the layer of polyimides.

Then quickly lay out a second layer of polyamide. After that, create a fiber optic placeholder using a 26 gauge cannula. Ensure that the cannula is lubricated using a Teflon based lubricant prior to being incorporated in the assembly.

Then apply a line of four to five millimeter epoxy perpendicular to the polyamide bundle. Once the epoxy has hardened, after two to three hours, remove the tape from the bottom layer and reapply the epoxy on the other side. After the epoxy has hardened, again, remove the 26 gauge cannula.

Make a cut in the middle using a razor blade to generate two polyamide matrices, each of which can be used for one hyperdrive. Now, print out the cone template on a sheet of transparency paper and cut a corresponding sheet of heavy duty aluminum foil. Apply a layer of epoxy to the aluminum foil and then quickly apply the transparency paper using a heavy object or a wooden dowel, smooth out the epoxy so that it is evenly distributed.

Next, cut out the cone template and clamp it together using an alligator clip. Finally, use another dab of epoxy to permanently affix the pieces to assemble the micro drive. First, attach the EIB to the drive body using two screws.

Then reinsert the 26 gauge cannula through the polyamide guide tube matrix. Align the polyamide matrix with the drive body using the fiber optic hole in the EIB to ensure that the guide tubes are perpendicular to the EIB. After that, attach the matrix to the drive body with epoxy and ensure that no epoxy flows into the guide tubes or into the drive body.

Finally, excess epoxy is removed using a dremel after that map each guide tube in the polyamide matrix to a corresponding bracket on the inner wall of the drive body. Slide a small ring of 33 gauge polyamide over each guide tube and into the bracket. Then apply a small amount of cyanoacrylate glue to affix each guide tube.

Finally, attach the whole apparatus to the inner wall of the drive body with epoxy and cut the polyamide so that they protrude just above the inner lip. Next, build a micro drive assembly by putting one of the custom built screws through the center hole of a top piece, followed by one of the five millimeter springs. Slide the outer hole of the top piece over one of the rails and gently drive the screw.

Then drive the screw until the spring reaches its minimum compressed length. And repeat this process for each rail micro drive. Afterward, turn the drive array upside down and take note of the arrangement of the guide tube matrix.

It is used later to map the location of the guide tube corresponding to each micro drive. Then record the identity of the corresponding micro drive. Now insert a poly IDE tube into each guide tube from the bottom of the drive base.

Let the carrier tube extend one to two millimeters from the top of the fully lowered micro drive. Then record the identity of the corresponding micro drive. On the photograph.

Attach the polyamide tube to the micro drive support with epoxy taking care not to let it run through the micro drive onto the spring or screw. Subsequently, cut all the polyimide tubes at the height of the micro drive screw head and flush at the bottom of the polyimide matrix. Afterward, mount the EIB to the drive base using two screws.

At this point, the drive array is ready to be loaded with stereo TROs or teros. After loading, invert the drive and carefully lower the shielding cone over the drive so that only the bottom piece protrudes affix the shielding cone by attaching the cone to the drive body with epoxy. After the cone is attached, strip a small piece of stainless steel wire and pin it to the EIB.

Scratch the inner aluminum part of the cone with a needle and ground the steel wire to the cone using silver paint. Once the silver paint has dried, reinforce it with a dab of epoxy. Here is an image of a freely moving mouse with the hyperdrive implanted.

And these are the examples of two single unit waveform recordings from this mouse. Shown here is a coronal section of the mouse brain highlighting the lateral genant nucleus where some of the electrodes were lowered. And here is an example of the para stimulus time histograms of two LGN neurons aligned to visual stimulation.

Here is the coronal section highlighting the hippocampus where another set of electrodes were lowered. An example of local field potential recording of a hippocampal ripple is shown here With the proper experience, a new hyperdrive can be assembled within one day. The drives developed in this procedure may be combined with other techniques such as optogenetics in order to stimulate and record from identified subpopulations of neurons.