fabrication of flat-interface nerve electrodes for recording neural activity

Fabrication of Flat-Interface Nerve Electrodes for Recording Neural Activity

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&#39; 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.

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1. Electrode Components Preparation
<ol>
	<li>Gather four electrode components that require precision cutting (laser cutting was used; please refer to the Materials List) before manufacturing. These components are (Figure 1): 
	Contacts array frame: This frame comprises a 125 &#181;m thick Polyether ether ketone (PEEK) sheet. It covers the entire width of the cuff and holds the middle contacts and has serpentine-shaped edges (Figure 1B). The middle contacts are wrapped in the guide channels; hence the exposed width of the contacts is limited by the width of the channels and the spacing is determined by the spacing between the channels. 
	The middle contacts strips: The middle contacts are formed by wrapping these strips around the contacts array frame (Figure 1B). Cut the strips out of the Platinum/10% Iridium sheet to the width of the guiding channels and add extra length to allow them to be fully folded around the frame. Spot-weld the contact&#39;s lead at 0&#186; angle with the strip&#39;s major axis. 
	The reference contacts: Four references are needed. The long dimension of these contacts is slightly shorter than the cuff width to fully contain them inside the cuff. Spot weld each reference contact to a lead at a 90&#186; angle with the contact&#39;s major axis. 
	PEEK spacers: Spacers create a thinner region on the electrode to allow bending and closing (Figure 1C). All the spacers are made from PEEK (other materials could be used) and cut to the length of the electrode. The width of the middle space is equal to the height of the electrode.</li>
</ol>
2. Contacts Array Preparation
<ol>
	<li>Clean the components made in step 1 by sonication in ethanol for 2 min at 40 KHz and room temperature, then 2 min in distilled deionized water under the same sonication parameters. Let dry.</li>
	<li>Visually inspect the contacts for any defects like laser-cut residuals or surface deformations.</li>
	<li>Position the contacts one by one under the microscope with the welding spot facing up. Starting from the free end, hold the contact with tweezers at approximately 1/3 of its length. Elevate the lead to a 45&#186; angle while holding the contact to make the first bend.</li>
	<li>Place the pre-bent contact underneath the array frame with the weld facing up. Hold the frame down with tweezers and elevate the lead to a 45&#186; angle to make a second bend. While Continuing to hold the frame down, grab the free end of the contact with tweezers and bend at a 180&#186; angle (fold toward the middle line of the frame).</li>
	<li>Straighten and pull the contact toward the operator and then bend at a 180&#186; angle (fold to the middle line). The spot welding point should now be enclosed in between the two bent ends.</li>
	<li>Repeat steps 2.3 - 2.5 for the remaining contacts. Make it as tight as possible. Alternate the contact leads on each side of the array frame.</li>
</ol>
3. Cuff Layout Guide
<ol>
	<li>Create a 2D diagram of the cuff in a flat open position. 
	NOTE: Use any CAD (Computer-aided design) software to produce a true-scale diagram. This diagram will determine the electrode dimensions and the placement site for the various electrode components.</li>
	<li>Print the 2D diagram on regular paper to scale using an ordinary printing machine, then cut out a 5 cm by 5 cm square piece with the drawing in the center.</li>
	<li>With a scalpel, cut out a 5 cm by 5 cm square piece of the thermal transparency sheet (T1).</li>
	<li>Place the transparency piece T1 on top of the diagram paper, and then place both layers on the base plate with the diagram facing up. Tape them down to the base plate with adhesive tape.</li>
</ol>
4. Electrode Base Layer and Reference Contacts Placement
<ol>
	<li>Cut out a 5 cm by 5 cm silicone sheet with a scalpel (S1) and place it on the transparency layer. Start by dropping one corner, then slowly lower the rest of the sheet to avoid trapping air bubbles between the T1 and S1 sheets (Figure 2A).</li>
	<li>Mix approximately 2 g of uncured silicone as the manufacturer&#39;s datasheet directs. Rigorously stir the two parts together with a sterilized wooden stirring stick. Place the mix in a vacuum chamber for 3 min. Cycle the vacuum to eliminate the bubbles as they rise to the surface. Preheat the isotemp oven to 130 &#186;C. 
	Note: Latex gloves can inhibit the curing process of silicone. They also contain sulfur, which can leave contaminants on the working surfaces. It is recommended that you use nitrile gloves instead.</li>
	<li>Using the dental pick tool, apply a thin line of uncured silicone along the middle of the spacer segments where they are located on the guiding diagram.</li>
	<li>Place the spacers onto the designated regions, and then press them down against the silicone sheet S1.</li>
	<li>Partially cure the silicone in the isotemp oven for 30 min, let it cool down for 10 min.</li>
	<li>Place the reference contacts onto designated areas. Ensure that the weld points are facing up and contact leads are routed towards the midline of the cuff to exit at the far end. After ensuring correct positioning, press the contacts down onto the silicone layer S1. Deposit uncured silicone into the through-holes.</li>
	<li>Tape down the leads and then fully cure the silicone at 130 &#186;C for 90 min, or overnight at room temperature (Figure 2B).</li>
</ol>
5. Center Contacts Array Placement
<ol>
	<li>Cut out 1.5 cm by 5 cm transparency piece with a scalpel (T2). Tape down the reference leads away from the middle region to prevent them from running underneath the contacts array during the next step.</li>
	<li>Place the contact arrays on the dedicated location with the leads side facing up. Deposit uncured silicone to tack the array in place.</li>
	<li>Place the piece from 5.1 (T2) across the midline of the electrode and over the arrays to hold them down. Tape the ends while pressing down on the arrays. Manually align the array with the dedicated position. Tape down the leads outside the cuff&#39;s perimeter.</li>
	<li>Place the small fixture bar across the center of the electrode and over the transparency segment T2. Clamp it down to the base plate with moderate pressure to press the middle contacts against the base silicone layer S1.</li>
	<li>Fully cure the silicone for 90 min at 130 &#186;C or overnight at RT.</li>
</ol>
6. Embedding the Electrode Components
<ol>
	<li>Remove the small fixture bar and gently remove the transparent sheet T2 to expose the middle contact arrays. Remove all the tapes holding the leads for references and middle contacts (Figure 2C).</li>
	<li>With a scalpel, cut a square piece of the transparency sheet to the same width as the electrode and 5 cm in length (T3), and then cut a square piece of silicone sheet to cover the entire electrode surface (S2).</li>
	<li>Lay the silicone sheet (S2) on top of the transparency piece (T3) and stretch it to remove any waves or irregularities and to eliminate air bubbles from being trapped in between.</li>
	<li>Cut four pieces of silicone tubing; 5 cm long each. Place them on the exit site of the leads as assigned on the guiding diagram. Leave a 2 mm space between the electrode and tube edges. While holding down each pair of tubes with tweezers, tape down the tubes starting at 1 mm away from the tube end. Repeat for the other pair.</li>
	<li>Arrange and lead of the middle contacts and the references into bundles, and then pass them through the corresponding tube near the exit sites. Repeat for the other three tubes. (Figure 2D).</li>
	<li>Deposit a generous amount of uncured silicone over the entire electrode body. 
	NOTE: Avoid forming air bubbles during this step by either slowly pouring the uncured silicone from the vacuumed mixing container or injecting it with a syringe.</li>
	<li>Place the structure from 6.3 on top of the deposited uncured silicone with the silicone sheet S2 facing down. Align the transparency piece T3 with the electrode while keeping the silicone sheet S2 adhered to it.</li>
	<li>Tape down the transparency piece T3 and then apply pressure to channel out any trapped air bubbles. Place the large fixture bar across the center of the electrode and over the transparency segment T3. Then, clamp it down to the base plate with moderate pressure. Fully cure the silicone for 90 min at 130 &#186;C, or overnight at RT.</li>
</ol>
7. Shielding Layer Placement (Recommended for Recording Cuffs)
<ol>
	<li>Remove the large fixture bar and delaminate the transparency piece (T3) with tweezers. Place the shielding sheet in the center of each face of the electrode and apply slight pressure to press them into the electrode. Deposit uncured silicone into the through-holes.</li>
	<li>Partially cure the silicone for 30 min at 130 &#186;C, and then let it cool completely to room temperature. Place adhesive tape over the outer ends of the electrode and over the closing flanges to prevent adding extra uncured silicone to these segments.</li>
	<li>Repeat steps 6.6 through 6.8.</li>
</ol>
8. Cutting out the Finished Electrode
<ol>
	<li>Peel off and cut the excess silicone on top of the adhesive tape added in step 7.2 using a scalpel blade, then carefully remove the adhesive tape.</li>
	<li>Cut out windows through the silicone to expose the spacer segments through the S2 layer. Extract the embedded spacer segments with tweezers. This step will leave voids and form a flexible single silicone sheet at these regions (originally S1).</li>
	<li>Peel off the excess silicone on top of the adhesive tapes that cover the silicone tubes, and then cut it with a scalpel blade to level the tubes with the electrode body.</li>
	<li>Cut around the perimeter of the electrode down to the base plate.</li>
	<li>Cut out a triangle between each tube pair completely through the base plate. On the outer side, follow the guiding diagram to shape the leads&#39; exit sites. Remove all the silicone material that was detached from the electrode body during the last steps.</li>
</ol>
9. Exposing Contacts and Shielding Layers
<ol>
	<li>Cut out windows through the silicone layer S2 that covers the shielding layer. Glide the polypropylene suture filament in between the electrode base (layer S1) and the transparent layer T1 on the base plate to delaminate the finished cuff electrode.</li>
	<li>Flip the electrode so that the center contacts and the silicone layer S1 are facing up, and then expose them by cutting out windows through the base silicone layer S1. Repeat this for the outer reference contacts, exposing 1 mm wide segments along the center of the contacts. Ensure that the stabilizing through-holes at the sides of the reference contacts are fully embedded inside the electrode&#39;s body.</li>
</ol>
10. Soldering a Connector to the Leads
<ol>
	<li>Deposit the soldering substance separately onto the leads and connecter pins, and then heat and fuse both parts together with a soldering iron. 
	Note: The DFT lead wires consist of a silver core surrounded by an outer layer made from the Nickel-Cobalt base alloy MP35N. Depositing the solder substance onto these wires requires the use of specialty flux to allow adhering to the wire (please refer to the Materials List).</li>
</ol>

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Platinum-Iridium foil</td>
			<td>Alfa Aesar</td>
			<td>41802</td>
			<td>90%Platinum Iridium</td>
		</tr>
		<tr>
			<td>DFT wires</td>
			<td>Fort Wayne Metals</td>
			<td>35N LT-DFT-28%Ag</td>
			<td></td>
		</tr>
		<tr>
			<td>Lead connector</td>
			<td>Omnetics Connector Corporation</td>
			<td>MCS-27-SS</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicone sheet</td>
			<td>Speciality Silicon Fabricator</td>
			<td>0.005&#34;x12&#34;x12&#34; Silicone Sheet</td>
			<td>High durometer, vulcanized</td>
		</tr>
		<tr>
			<td>Polyether ether ketone (PEEK) sheet</td>
			<td>Peek-Optima</td>
			<td>0.005 sheet LT3 grade</td>
			<td></td>
		</tr>
		<tr>
			<td>polyester stabelizing mesh</td>
			<td>Surgicalmesh</td>
			<td>PETKM2002</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicon tubing (0.04&#34; I.D. 0.085&#34; O.D.)</td>
			<td>Silcon Medical/NewAge Industries.</td>
			<td>2810458</td>
			<td></td>
		</tr>
		<tr>
			<td>Outer shielding layer</td>
			<td>Alfa Aesar, A Johnson Matthey</td>
			<td>MFCD00003436 (11391)</td>
			<td>Gold foil, 0.004&#34; thick</td>
		</tr>
		<tr>
			<td>Transparency sheet</td>
			<td>APOLLO</td>
			<td>APOCG7060</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrasonic bath cleaner</td>
			<td>Terra Universal</td>
			<td>2603-00A-220</td>
			<td></td>
		</tr>
		<tr>
			<td>Isotemp standard lab oven</td>
			<td>Fisher Scientific</td>
			<td>13247637G</td>
			<td></td>
		</tr>
		<tr>
			<td>Optical microscope</td>
			<td>Fisher Scientific</td>
			<td>15-000-101</td>
			<td></td>
		</tr>
		<tr>
			<td>Tweezers</td>
			<td>Technik</td>
			<td>18049USA (2A-SA)</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical blade handles</td>
			<td>Aspen Surgical Products</td>
			<td>371031</td>
			<td></td>
		</tr>
		<tr>
			<td>Base frame</td>
			<td>McMaster-Carr</td>
			<td>9785K411</td>
			<td></td>
		</tr>
		<tr>
			<td>Support beam</td>
			<td>McMaster-Carr</td>
			<td>9524K359</td>
			<td></td>
		</tr>
		<tr>
			<td>Two parts silicone</td>
			<td>Nusil</td>
			<td>MED 4765</td>
			<td></td>
		</tr>
		<tr>
			<td>Soldering Flux</td>
			<td>SRA Soldering Products</td>
			<td>FLS71</td>
			<td></td>
		</tr>
		<tr>
			<td>Tape</td>
			<td>3M Healthcare</td>
			<td>1535-0 (SKUMMM15350H)</td>
			<td>Paper, hypoallergenic surgical tape</td>
		</tr>
		<tr>
			<td>Spot welding machine</td>
			<td>Unitek</td>
			<td>125 Power Supply with 101F Welding Head</td>
			<td></td>
		</tr>
		<tr>
			<td>Laser cutting platform</td>
			<td>Universal Laser Systems</td>
			<td>PLS6.150D</td>
			<td>150 watts laser</td>
		</tr>
	</tbody>
</table>

Source: Dweiri, Y. M., et al. <a href="https://app.jove.com/v/54388">Fabrication of high contact-density, flat-interface nerve electrodes for recording and stimulation applications.</a> J. Vis. Exp. (2016)
This video demonstrates the fabrication of a flat nerve-wrapping electrode. It showcases the integration of shielding metal and precise polymer layering for an effective recording surface. The process involves attaching, curing, trimming, and cutting polymer layers for optimal nerve contact and accurate signal recording.

<img alt="Figure 1" src="/files/ftp_upload/22750/22750_Figure1.jpg" /> 
Figure 1: Overview of the FINE and its Components. A) FINE in the open position and the four main building components that require precision cut. These components are: Contacts array frame (I), the middle contacts strips (II), the reference contacts (III), PEEK spacers (IV). The cuff is facing downward with respect to the contacts placement against the nerve. The spacers (IV) are...

1. Electrode Components Preparation

	Gather four electrode components that require precision cutting (laser cutting was used; please refer to the ...

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.

30 ビュー. 神経活動を記録するためのフラットインターフェース神経電極の作製

ビデオ: 神経活動を記録するためのフラットインターフェース神経電極の作製 - 実験

Fabrication of Fine Electrodes on the Tip of Hypodermic Needle Using Photoresist Spray Coating and Flexible Photomask for Biomedical Applications

We have introduced a fabrication method for electrical impedance spectroscopy (EIS)-on-a-needle (EoN: EIS-on-a-needle) to locate target tissues in the body by measuring and analyzing differences in the electrical impedance between dissimilar biotissues. This paper describes the fabrication method of fine interdigitated electrodes (IDEs) at the tip of a hypodermic needle using a photoresist spray coating and flexible film photomask in the photolithography process. A polyethylene terephthalate (PET) heat shrink tube (HST) with a wall thickness of 25 &#181;m is employed as the insulation and passivation layer. The PET HST shows a higher mechanical durability compared with poly(p-xylylene) polymers, which have been widely used as a dielectric coating material. Furthermore, the HST shows good chemical resistance to most acids and bases, which is advantageous for limiting chemical damage to the EoN. The use of the EoN is especially preferred for the characterization of chemicals/biomaterials or fabrication using acidic/basic chemicals. The fabricated gap and width of the IDEs are as small as 20 &#181;m, and the overall width and length of the IDEs are 400 &#181;m and 860 &#181;m, respectively. The fabrication margin from the tip (distance between the tip of hypodermic needle and starting point of the IDEs) of the hypodermic needle is as small as 680 &#181;m, which indicates that unnecessarily excessive invasion into biotissues can be avoided during the electrical impedance measurement. The EoN has a high potential for clinical use, such as for thyroid biopsies and anesthesia drug delivery in a spinal space. Further, even in surgery that involves the partial resection of tumors, the EoN can be employed to preserve as much normal tissue as possible by detecting the surgical margin (normal tissue that is removed with the surgical excision of a tumor) between the normal and lesion tissues.

The fabrication method for fine interdigitated electrodes (gap and width: 20 &#181;m) at the tip of a hypodermic needle (diameter: 720 &#181;m) is demonstrated using a spray coating and flexible film photomask in the photolithography process.

医用フォトレジスト スプレー塗装と柔軟なフォトマスクを使用して皮下注射針の先端の微細電極の作製

We have introduced a fabrication method for electrical impedance spectroscopy (EIS)-on-a-needle (EoN: EIS-on-a-needle) to locate target tissues in the ...

JoVE Journal

神経科学

Open-source Toolkit: Benchtop Carbon Fiber Microelectrode Array for Nerve Recording

Conventional peripheral nerve probes are primarily fabricated in a cleanroom, requiring the use of multiple expensive and highly specialized tools. This paper presents a cleanroom "light" fabrication process of carbon fiber neural electrode arrays that can be learned quickly by an inexperienced cleanroom user. This carbon fiber electrode array fabrication process requires just one cleanroom tool, a Parylene C deposition machine, that can be learned quickly or outsourced to a commercial processing facility at marginal cost. This fabrication process also includes hand-populating printed circuit boards, insulation, and tip optimization. 
The three different tip optimizations explored here (Nd:YAG laser, blowtorch, and UV laser) result in a range of tip geometries and 1 kHz impedances, with blowtorched fibers resulting in the lowest impedance. While previous experiments have proven laser and blowtorch electrode efficacy, this paper also shows that UV laser-cut fibers can record neural signals in vivo. Existing carbon fiber arrays either do not have individuated electrodes in favor of bundles or require cleanroom fabricated guides for population and insulation. The proposed arrays use only tools that can be used at a benchtop for fiber population. This carbon fiber electrode array fabrication process allows for quick customization of bulk array fabrication at a reduced price compared to commercially available probes.

Here, we describe fabrication methodology for customizable carbon fiber electrode arrays for recording in vivo in nerve and brain.

オープンソースツールキット:神経記録用のベンチトップカーボンファイバーマイクロ電極アレイ

Conventional peripheral nerve probes are primarily fabricated in a cleanroom, requiring the use of multiple expensive and highly specialized tools. This ...

生物工学

Cavernous Nerve Stimulation and Recording of Intracavernous Pressure in a Rat

The stimulation of the cavernous nerve (CN) and measurement of intracavernous pressure (ICP) have been used extensively to test and evaluate therapies for erectile dysfunction. However, the methods used vary between laboratories, and pitfalls still exist. The goal of this study was to describe a surgical technique that would provide a reliable and reproducible model. By exposing the ischiocavernosus muscle at its point of insertion on the ischial tuberosity, the penile crus could be cannulated with minimal dissection and injury to the structures involved in erectile function. Repeated stimulation of the CN, without the need for lifting and drying, was achieved by using a 125 &#181;m bipolar silver electrode and biocompatible silicon glue to isolate the electrode-nerve complex. This method prevents neuropraxia by reducing stretching and drying the nerve and provides complete isolation of the nerve, negating electrical leakage and preventing stimulation of alternative pathways.

This study describes a simplified surgical procedure and technique for performing cavernous nerve stimulation with the isolation of the nerve-electrode complex using silicone glue and intracavernous pressure measurement.

海綿神経刺激とラットの海綿静脈洞部の圧力の記録

The stimulation of the cavernous nerve (CN) and measurement of intracavernous pressure (ICP) have been used extensively to test and evaluate therapies for ...