FMA Technology | Design and Architecture | Vacuum Inserter Tool | Titanium Pedistal | FAQ | Pricing | User Instructions | Layout Specifications Floating Microprocessor Array User Instructions Please Click Here to view FMA user instructions in a printer friendly PDF format. It is recommended that the FMA not be removed from the plastic container until after sterilization. The FMA has been tested and a data sheet has been provided for each FMA listing impedance, electrode length specifications, and other pertinent information about the FMA. I. Removal of FMA from plastic box. The ceramic substrate and microelectrodes are encapsulated in carbo wax (polyethylene glycol) in order to protect the microelectrodes during shipping and storage until the FMA is ready to implant. Polyimide (Kapton) tape is used to secure the FMA ceramic substrate to the plastic container. The connector has been placed onto double-sided tape to help secure the connector and Polyimide tape is placed over the connector and onto the plastic container to insure it does not move during shipping. The cable and ceramic substrate/electrode assembly have been made secure by taping a small piece of waxed paper over the cable near the ceramic substrate to insure the ceramic substrate does not move around during shipping. To release the FMA from the Polyimide tape, first completely remove the tape securing the cable. Next remove the tape that is over the connector and then grabbing onto the connector only (never grab onto the connector and cable at the same time) lift the connector off the double-sided tape by tilting the connector towards the ceramic substrate and simultaneously twisting the connector until it comes loose. Lay the connector on its side. Using a syringe flush the base of the ceramic substrate with isopropyl alcohol trying not to dissolve the carbo wax. The alcohol with dissolve the glue on the Polyimide tape releasing the ceramic substrate from the tape. The FMA assembly may now be lifted from the plastic container for testing or implantation. II. Dissolving the carbo wax away from the array Carbo wax can be easily dissolved in distilled water at room temperature. Heating the distilled water to 50 centigrade will decrease the time necessary to dissolve the carbo wax away from the substrate and electrodes. If the FMA needs to be used for testing or examination before implantation it is suggested that carbo wax be re-applied to the microelectrodes to protect it during storage, sterilization, and initial surgical implantation. To remove the carbo wax lower the ceramic substrate portion of the FMA into warm distilled water until all the carbo wax dissolves away. The FMA should always be held at the connector when handling. At 50 degrees centigrade the carbo wax should completely dissolve away in about 3 to 5 minutes. If the carbo wax is being dissolved at the time of surgery sterile water or saline should be used to dissolve the carbo wax. To re-apply carbo wax to the electrodes, heat the carbo wax powder in an aluminum dish at about 120° F. Use a thin, about 0.003” diameter, wire by collecting some of the dissolved carbo wax and message the drop of the melted carbo wax to the base of the ceramic substrate. Never touch the electrodes with the applicator. Continue to add additional carbo wax until all the electrodes including the tips have been encapsulated. III. Sterilization of the FMA It is recommended that the FMAs not be autoclaved. Although all the materials used to construct the FMAs are capable of withstanding autoclaving the fragile nature of the design and the need to employ a special housing to support the FMA during autoclaving make it not a desirable alternative to gas sterilization techniques. Tests, done at Cal Tech, are conclusive that the ethylene oxide will penetrate through the carbo wax and provide adequate sterilization for animal use. Proper out-gassing time (approx. 24 hours) should be allowed in order to insure all the gas has been eliminated from the FMA assembly and microelectrodes. IV. Implanting the FMA and using the vacuum inserter device The primary concern when handling the FMA prior and during implantation is to insure that the microelectrodes do not touch anything other than soft tissue. The microelectrode tips are very fragile and may bend if the electrode tips are allowed to come in contact with bone or any other hard surfaces. Our web site; www.microprobes.com, has a link to a recent paper by S. Musallam, et al, ref.1, that describes an implantation protocol for the FMAs, which may provide some additional information. In most cases the microelectrodes will want to be pointing 90 degrees relative to the top of the connector, however due to the curvature of the brain and bone it may be necessary to rotate the ceramic substrate relative to the connector. Before fixing the connector or titanium pedestal to the bone insure the microelectrodes will be pointing orthogonally to the surface of the neural tissue where the FMA will be implanted. The carbo wax does not have to be removed for this test. If the electrode shafts are not pointing in the desired direction for implantation the ceramic substrate can be rotated by holding onto the connector with one hand and carefully grabbing the cable with the thumb and index finger about 1 cm from the substrate and twisting the cable about 2 complete turns. Carefully release the cable and the substrate should assume a new position. Repeat as necessary to insure the microelectrodes are pointing in the correct direction relative to the surface of the neural tissue. The carbo wax should be dissolved after the connector has been secured to the bone by continual rinsing with warm saline or ringers solution. Make sure that the ceramic substrate and microelectrodes are being supported above the brain during this process. Although carbo wax is biocompatible and will flush away from the neural tissue it may be more convenient to lay a piece of sterile gauze over the tissue while the carbo wax is being dissolved from the FMA substrate. If the carbo wax has already been dissolved, supporting the ceramic substrate above the brain while securing the connector to the bone is essential to ensure that the delicate microelectrode tips are suspended in air and are protected during this process. Position the connector and manipulate the cable to ensure the array is over the intended location of insertion so that there will not be any forces on the array after it has been implanted. It is imperative that the microelectrodes be inserted perpendicular to the surface of the neural tissue. Attach the 16 gauge SS tube from the vacuum inserter system to an appropriated micro-drive system. The SS tube and Tygon tube attached to the SS tube should be disconnected from the coupling and sterilized prior to implantation. After the FMA connector or titanium pedestal have been secured to the bone, position the 16 gauge SS tube attached to the vacuum pump over the top of the substrate and turn the pump on. The top of the FMA array should be secured to the SS tube. Remove the support device used to keep the electrode off the brain and position the FMA over the area of the brain where the electrodes are to be lowered. Recent studies by several investigators working with the Utah array as well as MicroProbes’ Multi-electrode arrays have determined that the arrays should be inserted either at very high speeds (10 m/sec as with the insertion tool used with the Utah Arrays) or at very slow speeds. It is recommended that the FMAs be inserted very slowly. The FMA should be lowered until there is only a small amount of dimpling of the brain, about 3 mm or less. 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 after insertion. The concept of this procedure is to advance the FMA at a slow enough speed so as not to depress the pial membrane, which will compress the brain, during insertion of the electrodes. After the FMA has been totally implanted and the bottom of the ceramic substrate is flush against the pial surface, turn the vacuum pump off and slowly raise the SS tube off the top of the ceramic substrate. Several investigators have applied a very small drop of Medical Grade high viscosity biocompatible cyanoacrylate such as the Loctite #454 on the cable approximately 2 to 4 mm from the substrate or Dural edge to provide a strain relief for the cable. Refer to any number of current publications as to how to best secure and protect the intra-cranial vault and FMA implants after all the FMAs have been implanted. MicroProbes for Life Science will soon offer Polycarbonate clear chambers with standard trephine diameters, which will allow one to completely seal off the craniotomy. The chambers will have a fill hole at the top to allow injection of the sterile ringers solution within the chamber in order to re-establish the closed intracranial vault. These chambers will be clear also allowing one to visualize the implant site for the entire period of the implant, ref. 2 & 3. It is also very important to protect that portion of the cable that is implanted between the skull and skin assuming cranial cement will not be totally encapsulating the cable between the connector or pedestal and the craniotomy. Although additional silicone elastomer has been placed over this portion of the cable it may be a vulnerable point at which external forces imposed primarily by the animal that could jeopardize the integrity of the cable. V. Daily Impedance Checking It is highly recommended that the impedance values of the individual electrodes be checked on daily bases or when testing the animal. This will provide a day to day monitor of the integrity of the electrode tips in-vivo as well as provide an indicator as to other possible problems that sometime occur with chronic implants. Testing the impedance will indicate a sudden drop in impedance values across all the electrodes which many times is a result of the connector on the animal’s head getting dirty or moist from either the environment or the animal touching the connector. Cleaning the connector with alcohol and then air drying with can air will usually remove most contaminants and eliminate electrical shunting that can sometimes drastically reduce the signal to noise ratio of your recordings. Our optional titanium pedestals have screw on covers that utilize a silicone gasket to keep the connector free from contaminants. MicroProbes for Life Science offers a multi-channel impedance tester that can be used for up to 18 channels, model IMP-2MC. It can also be operated as a single electrode impedance tester. This will make daily impedance checks of the electrodes much quicker and easier. Polycarbonate Chamber References: 1. Salcman, M. and Bak, M. J. (1976) A new chronic recording intracortical microelectrode. Med. Biol. Eng., 14, 42-50. 2. Schmidt, E. M., Bak M. J. and McIntosh, J. L. (1976) Long-term chronic recording form cortical neurons. Exp. Neurol., 52, 496-506. Reference for FMA: Musallam, S., Bak, M., Troyk, P., and Andersen, R., “A Floating Metal Microelectrode Array for Chronic Implantation”, J. Neuroscience Methods 10.1016, 2006.09.005.