We presently offer three different electrode configurations at this time, although we have fabricated many custom designs for customers in the past. As you observe what our part numbers look like for our probes, as seen under our Product section, you will notice they have a part number like WE30031.0A5. The 00 portion of the part number specifies the microprobe configuration.
Monopolar Electrodes - 00
Implies no special mounting with the sharpened probe being insulated with Parylene-C, having the length, width, tip profile and impedance as specified in the tables for ordering your electrodes.
Polyimide Tubing - PT
Electrodes which have been mounted into polyimide tubing in order to increase the stiffness and provide additional insulation thickness. This mounting is typically recommended when fairly high impedance electrodes must penetrate deeper layers of the brain or spinal cord.
ST
Specifies our bipolar or stereotrodes. These electrodes when ordered with impedances less than 0.5 meohms are excellent for localizing stimulation current fields. Higher impedance stereotrodes are excellent for enhancing the isolation of single neural elements by simultaneous recording of multiple units on two closely spaced microelectrodes. The tip spacing is typically equal to the shaft diameter of one of the electrodes used in making the stereotrode. Different tip spacing is available upon request.
The M201 pin connectors are attached to the distal end of our electrodes. You can purchase these connectors as well as the mating connector, M202, by clicking here and going to our Accessory Page. Many users prefer to use our electrodes without any connector, which is fine. We will simply remove the connectors for you if requested. There is no discount for this since the connectors are attached at the beginning our fabrication process.
Tip exposures for Heat Tapered "H" tip profiles have approximately 15 to 20 percent MORE exposure.
Tip exposures for Blunted "B" tip profiles have approximately 15 to 20 percent LESS exposure.
Tip exposures for Extra Fine "F" tip profiles have approximately 10 to 15 percent MORE exposure.
Based on your selected options, a unique part number will be assigned to reflect the customized specifications. Reference this part number to place your order, or to correspond with our team members in Customer Service or Tech Support . See below for a part number example.
Yes, electrodes within any one array can be fabricated at any length between 0.5 mm and 10 mm. Use the FMA Design Sheet to specify individual lengths by their position in the array.
At this time we are offering either platinum/iridium (70/30%) or pure iridium as the electrode’s solid core conductors. Although tungsten is slightly stiffer it is not considered by most investigators to be as inert or biocompatible.
Selectable impedance values may range anywhere between 10 kilohm and 2.5 megohm, depending on your application. Impedance values may also differ for individual electrodes within an array. Also, it is possible to include an electrode with virtually zero impedance for ground or common, which is an un-insulated electrode.
Typically, the microelectrode tips are between 2 and 3 microns for most Platinum/Iridium electrodes. This may be varied for special applications, however. For example, we are currently supplying pure iridium electrodes for a visual prosthesis study that have a diameter range of 5 to 6 microns.
The microelectrodes are insulated with Parylene-C, a biocompatible polymer that has been successfully used for many years as the primary insulator for countless implantable devices and electrodes.
For FMAs requiring microelectrode lengths less than 2 mm, we recommend that at least 2 electrodes have lengths of 2.5 mm to act as anchoring pins. The anchoring pins provide necessary support to ensure that the array remains securely attached in the brain or spinal cord. These longer electrodes are typically chosen to be the reference and/or ground electrodes.
Yes. Although the FMAs were primarily designed for long-term chronic studies, they may also be used for acute studies where one needs to insure that the array will float with the brain during recording or stimulation protocols. If brain movement is not an issue, investigators typically use our Multi-Electrode Arrays.
Yes. Four is the minimum number of electrodes that may be ordered within a single FMA.
At this time we can guarantee the specified electrode length to be within 200 microns.
You can reuse an array that has been used for acute studies. It is recommended you clean the array in 50% bleach/distilled water. Chronically used FMAs are typically not reused because of tightly bound connective tissue around the FMA and cable.
Yes. You can specify different layout geometries that also require a different number of electrodes. We have provided custom-designed ceramic substrates for customers. There is a one-time non-reoccurring engineering (NRE) charge of $3800 to $7500 (typical) to have your own layout and implant geometry designed for your particular application. Inner electrode spacing must be within 250 to 1000 micron constraints. Please allow 2 to 3 months for delivery of FMAs with custom designed ceramic substrates.
No. At this time we use custom nano connectors made by Omnetics Corp., designed for the sonic bonding techniques needed to attach the fine gold wires from the FMA. We may provide interface cables that can be attached between the Omnetics A8141-001 type design of the FMA and your headstage amplifier connector.
Cable lengths may be specified from 1.5 cm to 12 cm.
Putting a slight kink in the cable between the point where the cable exits the bone edge and the implanted array will help provide necessary slack during potential brain to skull movements. Also many investigators have found that applying a very small amount of highly viscous biocompatible cyanoacrylate glue over the cable about 2 to 3 mm from the implanted array and securing the cable to the pial surface is very effective in eliminating movement of the device.
Keeping the subject relatively immobile during the first few days after implant is also recommended. This assists in the natural encapsulation of the array at the surface of the brain owing to normal tissue adhesions that occur around any foreign body implant.
The primary concern when handling the FMA prior to and during implantation is to ensure that the microelectrodes do not touch anything other than soft tissue. The microelectrode tips are very fragile and may bend if allowed to come in contact with bone or any other hard surface. It is imperative that the microelectrodes be implanted perpendicular to the surface of the brain to ensure minimal tissue disruption during insertion. We offer a vacuum inserter system, described in the user instructions, which is the preferred method of inserting the arrays.
It is recommended that the FMAs be inserted very slowly. The FMA should be lowered until there is just a small amount of dimpling of the brain. Allow the electrodes to penetrate the pial membrane before advancing the FMA further. Slowly lower the FMA into the brain, stopping the advancement every few hundred microns to allow the pial membrane to relax. The objective is to advance the FMA at a slow enough speed so as not to create a depression in the pial membrane, which will compress the brain tissue.
Tissue damage can be avoided by implementing the following precautions. First, try to avoid placing the electrodes over any blood vessels when making the initial positioning of the array for implantation. Second, ensure that the electrodes are as close to perpendicular to the brain’s surface as possible before lowering the array into the brain. And lastly, lower the array as slowly as possible into the brain.
It is possible to implant the array through dura for smaller animals, although this is not advised for chronic studies. One reason for this caution is that there maybe lateral relative movement between the pial and dura membranes, which may cause the electrodes tips to move, causing local adhesions near the tip.
The tubing, including the inserter wand, may be sterilized; although in most instances, it usually is only necessary to sterilize the tubing and cannula extending from the wand.
We used 0.001" (25 micron) gold wire from the ceramic substrate array to the connector. The cable is over-coated with MED6-6606 silicone elastomer for flexibility and strength.