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

Podsumowanie

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

Streszczenie

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.

Wprowadzenie

Much of neuroscience research relies upon recording neural signals using electrophysiology (ePhys). These neural signals are crucial to understanding the functions of neural networks and novel medical treatments such as brain machine and peripheral nerve interfaces^1,2,3,4,5,6. Research surrounding peripheral nerves requires custom-made or commercially available neural recording electrodes. Neural recording electrodes-unique tools with micron-scale dimensions and fragile materials-require a specialized set of skills and equipment to fabricate. A variety of specialized probes have been developed for specific end uses; however, this implies that experiments must be designed around currently available commercial probes, or a laboratory must invest in the development of a specialized probe, which is a lengthy process. Due to the wide variety of neural research in peripheral nerve, there is high demand for a versatile ePhys probe^4,7,8. An ideal ePhys probe would feature a small recording site, low impedance⁹, and a financially realistic price point for implementation in a system³.

Current commercial electrodes tend to either be extraneural or cuff electrodes (Neural Cuff¹⁰, MicroProbes Nerve Cuff Electrode¹¹), which sit outside the nerve, or intrafascicular, which penetrate the nerve and sit within the fascicle of interest. However, as cuff electrodes sit further away from the fibers, they pick up more noise from nearby muscles and other fascicles that may not be the target. These probes also tend to constrict the nerve, which can lead to biofouling-a build-up of glial cells and scar tissue-at the electrode interface while the tissue heals. Intrafascicular electrodes (such as LIFE¹², TIME¹³, and Utah Arrays¹⁴) add the benefit of fascicle selectivity and have good signal-to-noise ratios, which is important in discriminating signals for machine interfacing. However, these probes do have issues with biocompatibility, with nerves becoming deformed over time^3,15,16. When bought commercially, both these probes have static designs with no option for experiment-specific customization and are costly for newer laboratories.

In response to the high cost and biocompatibility issues presented by other probes, carbon fiber electrodes may offer an avenue for neuroscience laboratories to build their own probes without the need for specialized equipment. Carbon fibers are an alternative recording material with a small form factor that allows for low damage insertion. Carbon fibers provide better biocompatibility and considerably lower scar response than silicon^17,18,19 without the intensive cleanroom processing^5,13,14. Carbon fibers are flexible, durable, easily integrated with other biomaterials¹⁹, and can penetrate and record from nerve^7,20. Despite the many advantages of carbon fibers, many laboratories find the manual fabrication of these arrays arduous. Some groups²¹ combine carbon fibers into bundles that collectively result in a larger (~200 µm) diameter; however, to our knowledge, these bundles have not been verified in nerve. Others have fabricated individuated carbon fiber electrode arrays, although their methods require cleanroom-fabricated carbon fiber guides^22,23,24 and equipment to populate their arrays^17,23,24. To address this, we propose a method of fabricating a carbon fiber array that can be performed at the laboratory benchtop that allows for impromptu modifications. The resulting array maintains individuated electrode tips without specialized fiber populating tools. Additionally, multiple geometries are presented to match the needs of the research experiment. Building from previous work^8,17,22,25, this paper provides detailed methodologies to build and modify several styles of arrays manually with minimal cleanroom training time needed.

Protokół

All animal procedures were approved by the University of Michigan Institutional Animal Care and Use Committee.

1. Choosing a carbon fiber array

1. Choose a printed circuit board (PCB) from one of the three designs shown in Figure 1.
   NOTE: For this protocol, Flex Arrays will be the focus.
   1. Refer to PCB designs on the Chestek Lab website (https://chestekresearch.engin.umich.edu), free of charge and ready to be sent to and ordered for printing through a PCB printing house.
   2. See Table 1 for a summary of connectors for each board and their specifications to help choose the connector that will work for the specific experimental setup.

2. Soldering the connector to the circuit board

1. Set a soldering iron to 315 °C (600 °F).
2. Apply flux to all soldering pads on the PCB.
   NOTE: Flux within a tube can be squeezed across the pads, while flux in a pot can be applied with the wooden end of a cotton-tipped applicator by smearing the flux across all pads liberally.
3. Form small mounds of solder on the back pads of the Flex Array (Figure 2A).
4. Solder the bottom row of connector pins to the back row of solder pads (Figure 2B).
   NOTE: All board designs provided by the Chestek lab were designed so that the connectors would pair precisely with their designated board.
   1. To do this, solder the pins on either side of the connector with easy access to the solder mounds. Once secure, gently push the soldering iron tip between the front pins to solder the remaining connections in the back.
      NOTE: Once the back row of pins is secure, the rest of the connector will align with each pin above its assigned solder pad.
5. Solder the front row of pins to the board by applying a small amount of solder to each pin. Apply an additional layer of flux if soldering is not happening quickly.
   1. Clean excess flux away with 100% isopropyl alcohol (IPA) and a short bristle brush.
6. Encapsulate the soldered connections in delayed set epoxy (Figure 2 C,D) using a 23 G needle and 1 mL syringe placed bevel side down on the pins. Push epoxy through the syringe slowly so that it flows into and along the connections.
   1. Leave the board overnight so that the delayed set epoxy can cure.
      NOTE: While the product insert for the delayed set epoxy states that it cures in 30 min, leaving it overnight allows a more stable connection to form.
7. Secure the backside of the board to the sides of the connector by laying a small line of delayed set epoxy across the back side of the board and pulling that onto the edges of the connector.
   1. Leave the board to cure overnight again.
      ​NOTE: At this point, either store the arrays or continue the build. If pausing in the build, store the arrays in a clean, dry box at room temperature.

3. Fiber population

1. Cut a pulled glass capillary so that its tip fits between the traces of the array (Figure 3A).
   1. Using a glass puller and filament, make capillaries using the following settings: Heat = 900, Pull = 70, Velocity = 35, Time = 200, Pressure = 900.
      NOTE: Numbers are unitless and specific to this device (see the Table of Materials).
2. Use the wooden ends of two cotton-tipped applicators (one per each part of silver epoxy) to scoop a small, ~1:1 ratio of silver epoxy in a plastic dish and mix using the same sticks used to scoop. Discard the applicators after mixing.
3. Cut 2-4 mm off the end of the carbon fiber bundle onto a piece of printer paper using a razor blade. To easily separate the fibers in the bundle, which are difficult to tease apart, pull a laminated piece of paper gently over the top of the bundle.
   NOTE: The laminated piece of paper transfers static into the fibers, which will separate by themselves.
4. Apply silver epoxy between every other pair of traces on one side of the board with the glass capillary (Figure 3B).
   1. Take a small drop of epoxy onto the end of a pulled capillary. Gently apply between every other trace on the end of the board, filling the gap.
      NOTE: The gap should be filled to the top of the two traces without overflowing to touch neighboring traces. Each trace is connected to one channel. This method of epoxy population means that each fiber will have two channels connected to it. This is because two traces allow for better fiber alignment, and redundancy in channel helps ensure electrical connection.
5. Use Teflon-coated tweezers to place one carbon fiber in each epoxy trace (Figure 3C).
6. Use a clean pulled capillary to adjust the carbon fibers, so they are perpendicular to the end of the Flex Array board and buried beneath the epoxy (Figure 3D).
7. Place the arrays on a wooden block with fibered ends overhanging the edge of the block.
   NOTE: The weight of the back end will keep the array on the block.
8. Bake the wooden block and arrays at 140 °C for 20 min to cure the silver epoxy and lock the fibers into place.
9. Repeat steps 3.4-3.8 for the other side of the board.
   NOTE: Arrays can be stored after any baking step; however, static from the storage boxes may cause the fibers to pull away from the board if too little silver epoxy was applied when populating the board.
   1. Create a raised adhesive platform within a box so that the bulk of the board can be stuck to the adhesive allowing the fibered ends of the board to be suspended within the box to prevent fiber breakage. Store at room temperature.
      NOTE: If fibers pull away from the board during storage, scrape the epoxy out of the traces with a clean pulled glass capillary and repeat steps 3.1-3.8 to replace the fibers. From this point on, arrays must be stored with the fibers suspended in this manner to prevent fiber breakage.

4. Applying ultra-violet (UV) epoxy to insulate the carbon fibers

1. Use a clean capillary and apply a small droplet (~0.5 mm in diameter of UV epoxy on the exposed traces on one side of the board (Figure 4A). Continue to add UV epoxy droplets until the traces are completely covered.
   NOTE: Do not allow the UV epoxy to get on the carbon fibers past the end of the PCB to ensure a smooth insertion later.
2. Cure the UV epoxy under a UV pen light for 2 min (Figure 4B).
3. Repeat steps 4.1-4.2 for the other side of the board.
4. Cut the fibers to 1 mm using a stereoscope reticle and surgical scissors.
   NOTE: Arrays can be stored at this point until ready to proceed to the next steps. They should be stored in a box that will elevate the carbon fibers away from the box itself. Arrays can be stored at room temperature indefinitely.

5. Checking electrical connections with 1 kHz impedance scans (Figure 5)

1. Submerge carbon fibers 1 mm into 1x phosphate-buffered saline (PBS).
2. To complete the circuit, use a silver-silver chloride (Ag|AgCl) reference electrode and a stainless steel rod (counter electrode).
   1. Using a beaker clamp, suspend the Ag|AgCl electrode in the 1x PBS and connect it to the reference of the impedance system being used.
   2. Using a beaker clamp, suspend the stainless steel rod in the 1x PBS and connect to the counter electrode input of the impedance system being used.
3. Run a 1 kHz impedance scan for each fiber using a potentiostat set to a 1 kHz scan frequency at 0.01 V_rms in a single sine waveform. Set the potentiostat to 0 V at the beginning of each scan for 5 s to stabilize the recorded signal. Record the measurements via the potentiostat-associated software.
   NOTE: Measurements can be taken at any point in the build; however, they are only necessary before insulation and during tip preparation. Table 2 lists typical ranges of impedances after each build step at 1 kHz for the user's reference.
4. Rinse the fibers in deionized (DI) water by dipping them into a small beaker three times and leave them to dry at room temperature.
   NOTE: Arrays can be left in storage until the user can continue onto the next step.

6. Parylene C Insulation

NOTE: Parylene C was chosen as the insulation material for the carbon fibers as it can be deposited at room temperature over batches of arrays and provides a highly conformal coating.

1. Mask the Flex Array connector using the mating connector.
2. Place a batch of 8-12 arrays into a storage box with a raised adhesive platform so that they can be insulated in one run. Place the arrays so that the connector end of the array is on the adhesive platform with the fibered end of the array overhanging (Figure 6) to prevent the fibers from sticking to the adhesive and pulling off and to ensure a uniform Parylene coating on the fibers.
3. Coat the arrays in a Parylene C deposition system to a thickness of 800 nm in a cleanroom, wearing appropriate personal protection equipment (PPE) as defined by the individual cleanroom being used.
   NOTE: Here, PPE was defined as cleanroom shoes, suit, head covering, goggles, mask, and latex gloves. It should be noted that this is standard PPE for entering a cleanroom. This step can be outsourced to a Parylene coating company for a fee; however, a commercial service may be able to coat more arrays at one time. Each Parylene C deposition system may have different safety precautions. Contact the technician before use to ensure user safety.
4. Remove the mating connector used as a mask from the Flex Array.
5. Place the arrays into a new box for storage until ready to use.

7. Tip preparation methods

NOTE: Two tip preparations in this section use lasers to cut fibers. Proper PPE, such as goggles resistant to the wavelengths used, should always be worn when using the laser, and other lab users in the vicinity of the laser should also be in PPE. Although fiber lengths listed in these steps are recommended lengths, users may try any length that suits their needs. The user must choose one of the following tip preparation methods as scissor cutting alone will not suffice to re-expose the electrode²⁵.

1. Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser cut
   1. Cut the fibers to 550 µm with surgical scissors.
   2. Use a 532nm Nd:YAG pulsed laser (5 mJ/pulse, 5 ns duration, 900 mW) to cut 50 µm off the tip of the fibers to re-expose the carbon underneath the Parylene C (usually takes 2-3 pulses).
      1. Align the fiber tips using the built-in stereoscope that comes with this laser system.
         NOTE: This system allows the user to align a window (here, 50 µm x 20 µm (height x width)) was used to encompass the end of the fiber.
      2. Focus the stereoscope on the end of the fiber at 500x magnification for an accurate and precise cut.
         NOTE: Parylene C will ablate slightly (<10 µm) from the tip leaving a blunt, cylindrical tip.
2. Blowtorch Sharpening^25,26,27
   1. Cut the fibers to 300 µm with surgical scissors.
   2. Submerge the array in a dish of deionized water, connector side down, and secured to the bottom of the dish with a small amount of putty.
   3. Use a pen camera to align the fibers with the surface of the water so that the fibers are just barely touching the surface of the water.
   4. Adjust a butane blowtorch flame to 3-5 mm and run it over the top of the fibers in a back-and-forth motion to sharpen fibers.
      NOTE: Fiber tips will glow orange when the flame passes over them.
   5. Remove the array from the putty and inspect it under a stereoscope for pointed tips under 50x magnification.
      NOTE: If pointed tips are observed, then no further blowtorching is necessary. If tips appear blunt, repeat steps 7.2.2-7.2.5.
3. UV laser cut²⁸
   ​NOTE: UV Laser can only be used on zero insertion force (ZIF) and Wide Board designs at present due to the large focal point of the UV Laser used being larger than the pitch of the Flex Array carbon fibers.
   1. Cut the carbon fibers to 1 mm with surgical scissors.
   2. Affix a UV laser to three orthogonally configured motorized stages.
      NOTE: The UV laser is a multimode Indium Gallium Nitride (InGaN) semiconductor with 1.5 W output power and 405 nm wavelength.
      1. Ensure that the laser has a continuous beam for fast and effective alignment and cutting.
   3. Secure the array in place to keep a still, level plane of electrodes for the laser to pass over. Ensure that array is held at an appropriate distance from the laser so that the fibers will be in light with the laser's focal point. To do this, provide a lower power to the laser and adjust the distance to best focus on the fiber²⁸.
   4. Move the UV laser focal point across the fiber plane at a speed of 25 µm/s to cut the fibers to the desired length (here, all fibers are cut to 500 µm).
      ​NOTE: Fibers will emit a bright light before being cut. Store the fibers after treatment until they are ready to be coated with a conductive polymer.

8. Poly(3,4-ethylenedioxythiophene):p-toluenesulfonate (PEDOT:pTS) conductive coating for lowered impedance

1. Mix solutions of 0.01 M 3,4-ethylenedioxythiophene and 0.1 M sodium p-toluenesulfonate in 50 mL of DI water and stir overnight on a stir plate (~450 rpm) or until no particulates can be observed in the solution.
   NOTE: Store the solution in a light-resistant container. Refrigerate the solution after mixing to keep the solution useable for up to 30 days.
2. Run a 1 kHz impedance scan using the same parameters as before (steps 5.2-5.3) in 1x PBS. Note which fibers have a good connection (<1 MΩ, typically 14-16 of 16 fibers).
3. Electroplate with PEDOT:pTS to lower the impedance of the electrodes.
   1. Submerge the fiber tips in PEDOT:pTS solution.
   2. Follow the steps outlaid in step 5.2, switching the 1x PBS solution out for PEDOT:pTS and short all connections to the board to the applied current channel.
   3. Apply 600 pA per good fiber for 600 s using a potentiostat.
   4. Turn the cell off and allow it to rest for 5 s at the end of the run.
4. Remove the fibers from the solution and rinse them in DI water.
5. Retake 1 kHz impedances to check that the fibers were successfully coated (use the same parameters listed in steps 5.2-5.3).
   NOTE: Good fibers are designated as any fiber having an impedance of less than 110 kΩ.

9. Connecting ground and reference wires

1. Gently scrape away Parylene C from the ground and reference vias on the board using tweezers. Short the ground and reference vias together in pairs on this board design.
   NOTE: Ground and reference vias can be found near the connector on the Flex array and are the four small gold circles near the connectors. Users will only need to remove Parylene C from the vias closest to the carbon fibers for measurements.
2. Cut two 5 cm lengths of insulated silver wire with a razor blade. Deinsulate the ends of the wires 2-3 mm from one end to be attached to the Flex Array and ~10 mm from the opposite ends to allow for easier grounding and referencing during surgery.
3. Heat the soldering iron back to 600 °F. Apply a small amount of flux to the vias.
4. Insert one wire (2-3 mm exposed end) into each of the ePhys vias on the board. Apply solder to the top of the vias (Figure 7A). Allow the probe to cool, then flip it over to apply a small amount of solder to the backside of the via (Figure 7A).
5. Using surgical scissors, snip off any exposed wire sticking out of the back solder mound as this helps reduce noise seen in recording (Figure 7B).
6. Place the arrays back into the storage box, bending the wires back and away from the fiber. Secure the wires on the adhesive tape to prevent potential fiber-wire interactions (Figure 7C).

10. Surgical procedure

NOTE: Rat cortex was used to test the efficacy of the UV Laser-prepared fibers as this has been described previously^7,20. These probes will work in nerve due to their similar geometry and impedance levels to blowtorch prepared fibers. This surgery was performed with an abundance of caution to validate that the UV laser did not change the response of the electrodes.

1. Anesthetize an adult male Long Evans rat using a combination of ketamine (90 mg/kg) and xylazine (10 mg/kg). Confirm anesthesia with a toe pinch test. Apply ointment to the eyes to prevent the rat's eyes from drying out during the surgery.
2. Create a 2 mm x 2 mm craniotomy above the right hemisphere's motor cortex. Identify the lower left corner of the craniotomy by measuring 1 mm anterior of bregma and 1 mm lateral of midline.
3. Mount the array into a stereotaxic instrument, and zero the stereotaxic instrument at the dura by gently lowering the fibers until they touch the dura's surface. Raise the array away from the surgical site and move it to the side until it is ready for insertion.
4. Resect the dura by gently pulling a needle with a barbed end over the surface of the tissue. Once a portion of the dura opens to the brain, use a pair of fine forceps to further assist in pulling away the dura.
5. Insert the fibers into the craniotomy and 1.2 mm into the brain using a stereotaxic instrument, lowering slowly by hand.
6. Record ePhys data for 10 min with an ePhys-specific headstage and preamplifier.
   1. Set the preamplifier high-pass filter to process the signal at 2.2 Hz, antialias at 7.5 kHz, and sample at 25 kHz.
      NOTE: For these measurements, only spontaneous activity is recorded. No stimulus is applied.
7. Euthanasia
   1. Place the rat under isoflurane at 5% under 1 L/min of oxygen until signs of life have ceased (20-30 min). Confirm euthanasia with decapitation.

11. Spike sorting

1. Use spike-sorting software to sort and analyze the data using previously reported methods⁸.
2. Use a high-pass filter on all channels (250 Hz corner, 4^th order Butterworth), and set the waveform detection level to -3.5 × RMS threshold.
   1. Use a Gaussian model to cluster and spikes with similar characteristics. Combine and average clusters of at least 10 waveforms to include in further analysis.
   2. Eliminate or delete all waveforms that are not spikes from the data set.
3. Export data once all channels have been sorted and use analysis software to plot and further analyze the waveforms.

12. Scanning electron microscopic (SEM) imaging

NOTE: This step will render arrays unusable and should be used only to inspect tip treatment results to check that the arrays are being properly processed. This step does not need to be done to build a successful array. Summarized below is a general outline of the SEM process; however, users who have not previously used SEM should receive help from a trained user.

1. Snip off the fibered end of the PCB and mount it on a carbon tape-masked SEM stub. Place the arrays on a small platform of stacked carbon tape (4-5 layers) to prevent the carbon fibers from sticking to the SEM stub.
2. Sputter-coat the arrays with gold (100-300 Å) following procedures outlined by the manufacturer of the gold sputter coater.
3. To inspect the tip treatment effects, image the arrays in an SEM at a working distance of 15 mm and 20 kV beam strength.
   NOTE: Arrays can be imaged without sputter-coating under a low vacuum, as shown in Figure 8D for UV laser-cut fibers. For this setup, it is recommended to have a working distance of 11-12 mm and a 4 kV beam strength.

Wyniki

Tip validation: SEM images
Previous work²⁰ showed that scissor cutting resulted in unreliable impedances as Parylene C folded across the recording site. Scissor cutting is used here only to cut fibers to the desired length before processing with an additional finish cutting method. SEM images of the tips were used to determine the exposed carbon length and tip geometry (Figure 8).

Scissor and Nd:YAG laser-cut fibers w...

Dyskusje

Material substitutions
While all materials used are summarized in the Table of Materials, very few of the materials are required to come from specific vendors. The Flex Array board must come from the listed vendor as they are the only company that can print the flexible board. The Flex Array connector must also be ordered from the vendor listed as it is a proprietary connector. Parylene C is highly recommended as the insulation material for the fibers as it provides a conformal coa...

Materiały

Name	Company	Catalog Number	Comments
3 prong clams	05-769-6Q	Fisher	Qty: 2 Unit Cost (USD): 20
3,4-ethylenedioxythiophene (25 g) (PEDOT)	96618	Sigma-Aldrich	Qty: 1 Unit Cost (USD): 102
353ND-T Epoxy (8oz)++ (ZIF and Wide Board Only)	353ND-T/8OZ	Epoxy Technology	Qty: 1 Unit Cost (USD): 48
Ag/AgCl (3M NaCl) Reference Electrode (pack of 3)	50-854-570	Fisher	Qty: 1 Unit Cost (USD): 100
Autolab	PGSTAT12	Metrohm
Blowtorch	1WG61	Grainger	Qty: 1 Unit Cost (USD): 36
Carbon Fibers	T-650/35 3K	Cytec Thornel	Qty: 1 Unit Cost (USD): n/a
Carbon tape	NC1784521	Fisher	Qty: 1 Unit Cost (USD): 27
Cotton Tipped Applicator	WOD1002	MediChoice	Qty: 1 Unit Cost (USD): 0.57
Delayed Set Epoxy++	1FBG8	Grainger	Qty: 1 Unit Cost (USD): 3
DI Water	n/a	n/a	Qty: n/a Unit Cost (USD): n/a
Dumont Tweezers #5	50-822-409	Fisher	Qty: 1 Unit Cost (USD): 73
Flex Array**	n/a	MicroConnex	Qty: 1 Unit Cost (USD): 68
Flux	SMD291ST8CC	DigiKey	Qty: 1 Unit Cost (USD): 13
Glass Capillaries (pack of 350)	50-821-986	Fisher	Qty: 1 Unit Cost (USD): 60
Glass Dish	n/a	n/a	Qty: 1 Unit Cost (USD): n/a
Hirose Connector (ZIF Only)	H3859CT-ND	DigiKey	Qty: 2 Unit Cost (USD): 2
Light-resistant Glass Bottle	n/a	Fisher	Qty: 1 Unit Cost (USD): n/a
Micropipette Heating Filiment	FB315B	Sutter Instrument Co	Qty: 1 Unit Cost (USD): n/a
Micropipette Puller	P-97	Sutter Instrument Co	Qty: 1 Unit Cost (USD): n/a
Nitrile Gloves (pack of 200)	19-041-171C	Fisher	Qty: 1 Unit Cost (USD): 47
Offline Sorter software	n/a	Plexon	Qty: 1 Unit Cost (USD): n/a
Omnetics Connector* (Flex Array Only)	A79025-001	Omnetics Inc	Qty: 1 Unit Cost (USD): 35
Omnetics Connector* (Flex Array Only)	A79024-001	Omnetics Inc	Qty: 1 Unit Cost (USD): 35
Omnetics to ZIF connector	ZCA-OMN16	Tucker-Davis Technologies	Qty: 1 Unit Cost (USD): n/a
Pin Terminal Connector (Wide Board Only)	ED11523-ND	DigiKey	Qty: 16 Unit Cost (USD): 10
Probe storage box	G2085	Melmat	Qty: 1 Unit Cost (USD): 2
Razor Blade	4A807	Grainger	Qty: 1 Unit Cost (USD): 2
SEM post	16327	lnf	Qty: 1 Unit Cost (USD): 3
Silver Epoxy (1oz)++	H20E/1OZ	Epoxy Technology	Qty: 1 Unit Cost (USD): 125
Silver GND REF wires	50-822-122	Fisher	Qty: 1 Unit Cost (USD): 423.2
Sodium p-toulenesulphonate(pTS)- 100g	152536	Sigma-Aldrich	Qty: 1 Unit Cost (USD): 59
Solder	24-6337-9703	DigiKey	Qty: 1 Unit Cost (USD): 60
Soldering Iron Tip	T0054449899N-ND	Digikey	Qty: 1 Unit Cost (USD): 13
Soldering Station	WD1002N-ND	Digikey	Qty: 1 Unit Cost (USD): 374
SpotCure-B UV LED Cure System	n/a	FusionNet LLC	Qty: 1 Unit Cost (USD): 895
Stainless steel rod	n/a	n/a	Qty: 1 Unit Cost (USD): n/a
Stir Plate	n/a	Fisher	Qty: 1 Unit Cost (USD): n/a
Surgical Scissors	08-953-1B	Fisher	Qty: 1 Unit Cost (USD): 100
TDT Shroud (ZIF Only)	Z3_ZC16SHRD_RSN	TDT	Qty: 1 Unit Cost (USD): 3.5
Teflon Tweezers	50-380-043	Fisher	Qty: 1 Unit Cost (USD): 47
UV & Visible Light Safety Glassees	92522	Loctite	Qty: 1 Unit Cost (USD): 45
UV Epoxy (8oz)++ (Flex Array Only)	OG142-87/8OZ	Epoxy Technology	Qty: 1 Unit Cost (USD): 83
UV Laser	n/a	WER	Qty: 1 Unit Cost (USD): 30
Weigh boat (pack of 500)	08-732-112	Fisher	Qty: 1 Unit Cost (USD): 58
Wide Board+	n/a	Advanced Circuits	Qty: 1 Unit Cost (USD): 3
ZIF Active Headstage	ZC16	Tucker-Davis Technologies	Qty: 1 Unit Cost (USD): 925
ZIF Passive Headstage	ZC16-P	Tucker-Davis Technologies	Qty: 1 Unit Cost (USD): 625
ZIF*	n/a	Coast to Coast Circuits	Qty: 1 Unit Cost (USD): 9