Brain tissue reaction to some chronically implanted metals
TL;DR: The toxicity of certain metals was evaluated histologically following chronic implantation for 2 months in the brains of cats and all but silver were found to be nontoxic.
Abstract: ✓ The toxicity of certain metals, namely, platinum, platinum-8% tungsten, platinum-10% rhodium, platinum-10% iridium, platinum-10% nickel, platinized platinum, a gold-nickel-chromium alloy, a gold-palladium-rhodium alloy, a chromium-nickel-molybdenum alloy (Vitallium), stainless steel, silver, rhenium, and gold, was evaluated histologically following chronic implantation for 2 months in the brains of cats. Of the above metals, all but silver were found to be nontoxic. Boron was also evaluated and found to be nontoxic.
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TL;DR: The physical basis for electrical stimulation of excitable tissue, as used by electrophysiological researchers and clinicians in functional electrical stimulation, is presented with emphasis on the fundamental mechanisms of charge injection at the electrode/tissue interface.
1,875 citations
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...The noble metals, including platinum (Pt), gold (Au), ir um (Ir), palladium (Pd), and rhodium (Rh), have been c only used for electrical stimulation, largely due to th elative resistance to corrosion (Dymond et al., 1970; Whit nd Gross, 1974; Johnson and Hench, 1977)....
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...Dymond et al. (1970)tested the toxicity of several metals implanted into the cat cerebral cortex for 2 months....
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TL;DR: Persistent ED1 up-regulation and neuronal loss was not observed in microelectrode stab controls indicating that the phenotype did not result from the initial mechanical trauma of electrode implantation, but was associated with the foreign body response.
834 citations
Cites background from "Brain tissue reaction to some chron..."
...…that is similar to that observed following the implantation of other materials in the brain and spinal cord (Aebischer et al., 1988; Campioni et al., 1998; Dymond et al., 1970; Edell et al., 1992; Powell et al., 1990; Stensaas and Stensaas, 1976, 1978; Winn et al., 1989; Yuen and Agnew, 1995)....
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...Our findings suggest a potential new mechanism for chronic recording failure that involves neuronal cell loss, which we speculate is caused by chronic inflammation at the microelectrode brain tissue interface....
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TL;DR: Results of pitch-matching experiments with the unilaterally deaf volunteer were consistent with tonotopic maps of the cochlea, and experiments indicated that a pitch continuum may be achieved by combining place and periodicity pitch modulation.
Abstract: Although single-channel electrode arrays implanted in the scala tympani of deaf patients are useful as an aid to lip reading and for distinguishing some environmental sounds, they do not transmit intelligible speech. However, multichannel electrode arrays, which take advantage of the cochlea's tonotopic organization, may be capable of generating the complex patterns of neural activity necessary for speech discrimination. In this study, multichannel electrodes were implanted in the cochleas of four volunteers, with access to the connecting wires made through the skin via a percutaneous connector. The major portion of the data presented is from two of these subjects: one has been bilaterally deaf since birth and the other has been unilaterally deaf for 15 years. Preliminary results of experiments with two more recently implanted subjects are described as well as experiments with a fifth volunteer who was implanted with five electrodes by House in 1969. Data on pitch and loudness discrimination as well as the effects of stimulation parameters on threshold, impedance, and electrode interaction are presented. Place pitch and periodicity pitch were observed in all five volunteers. The results of pitch-matching experiments with the unilaterally deaf volunteer were consistent with tonotopic maps of the cochlea, and experiments indicated that a pitch continuum may be achieved by combining place and periodicity pitch modulation. Preliminary experiments in tune recognition with one subject demonstrate his ability to recognize simple melodies based on periodicity pitch cues. These results, coupled with the finding that subjective sensations remain stable over the long-term, support the feasibility of providing artificial hearing with a multichannel cochlear stimulation system.
346 citations
TL;DR: Three conceptually safe methods of injecting charge from a noble metal into tissue: modification of the electrical double layer at the interface and coupling via either of two symmetrical surface-layer oxidation-reduction processes.
Abstract: Electrical stimulation of the nervous system is of increasing importance for a variety of prospective neural prostheses. Electrochemical reactions which may occur at Pt or other noble metal-tissue interfaces are reviewed. Use of stimulus waveforms with a net direct current component increases the probability of tissue damage. There are three conceptually safe methods of injecting charge from a noble metal into tissue: modification of the electrical double layer at the interface and coupling via either of two symmetrical surface-layer oxidation-reduction processes. These reactions may be addressed with stimulus waveforms without a direct current component and with controlled charge densities.
329 citations
TL;DR: This review provides a comprehensive reflection on the current understanding of the key failure modes that may impact intracortical microelectrode performance and presents the vision on the future directions of materials-based treatments for neural interfacing.
Abstract: To ensure long-term consistent neural recordings, next-generation intracortical microelectrodes are being developed with an increased emphasis on reducing the neuro-inflammatory response. The increased emphasis stems from the improved understanding of the multifaceted role that inflammation may play in disrupting both biologic and abiologic components of the overall neural interface circuit. To combat neuro-inflammation and improve recording quality, the field is actively progressing from traditional inorganic materials towards approaches that either minimizes the microelectrode footprint or that incorporate compliant materials, bioactive molecules, conducting polymers or nanomaterials. However, the immune-privileged cortical tissue introduces an added complexity compared to other biomedical applications that remains to be fully understood. This review provides a comprehensive reflection on the current understanding of the key failure modes that may impact intracortical microelectrode performance. In addition, a detailed overview of the current status of various materials-based approaches that have gained interest for neural interfacing applications is presented, and key challenges that remain to be overcome are discussed. Finally, we present our vision on the future directions of materials-based treatments to improve intracortical microelectrodes for neural interfacing.
319 citations
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96 citations
TL;DR: The investigation has thrown light on certain factors controlling gliosis and points to a fundamental principle involved in surgery of the brain.
Abstract: In a series of experimental punctures of the brain performed by one of us, 1 it was observed that, in addition to the usual scar composed of connective tissue and neuroglia, open tracks which did not contain any connective tissue and which were surrounded by little if any gliosis occasionally resulted. In the hope of explaining these variations, we have compared the result obtained from leaving injured brain tissue in place with the result following removal of an equal portion of such tissue. The investigation has thrown light on certain factors controlling gliosis and points to a fundamental principle involved in surgery of the brain. LITERATURE In general, the literature shows that wounds produced in experimental puncture of the brain have frequently been made by heated blunt needles (Tschistowitsch, 2 Coen, 3 Macklin and Macklin 4 and others). This produces a wide zone of injured tissue. The conclusions reached by
80 citations
TL;DR: A review of the literature has failed to reveal a detailed chronological study of the finer microscopic changes in the central nervous system that take place consequent to implanted electrodes, and the neurophysiological literature contains a paucity of detailed histopathological examinations of sacrificed experimental animals.
Abstract: W ITIt the introduction of the Horsley-Clarke 13 stereotaxic instrument in 1908, a method became available for the investigation of the physiology of the central nervous system which has the advantage of precise localization to specific structures. Implantation of electrodes provided neurophysiologists with a useful method in studying neuronal mechanisms. With the development of the chronic electrode technique by Loucks 1~ and its wide application in animals by Hess, ~2 it became possible to study the relation of functions to structures of the nervous system in animals avoiding anesthesia, chemical restraint and extensive trauma. This technique has been further extended recently to humans suffering from neurological and psychiatric diseases. 2'3'8'~~176 One of the questions that has arisen out of the technique of implanting electrodes, and which has stimulated the present work, is the extent and the amount of tissue destruction and reaction caused by the insertion of electrodes into brain tissue and the effect of the prolonged presence of such a foreign body. This problem has assumed paramount importance since features of this destruction must be kept to a minimum if analyses of the physiologic results are to be meaningful, particularly in reference to possible residual damage in humans. Although of prime importance to investigators, a review of the literature has failed to reveal a detailed chronological study of the finer microscopic changes in the central nervous system that take place consequent to implanted electrodes. The neurophysiological literature contains a paucity of detailed histopathological examinations of sacrificed experimental animals. Many investigators have described the pathology in such general and nondescript statements as a \"slight,\" \"moderate,\" or \"mild\" gliosis for varying distances around the electrode track, while others have given no account of the histopathological characteristics of the electrode tracks and surrounding tissue. Fisher and Sayre 9 found evidence in studies on animals that the reaction around the electrode may occur within 1 mm. from the track. Dodge et al. s have recently reported minimal microscopic changes in 1 human 19 months after intracerebral electrography.
72 citations
TL;DR: Conclusions 6, 7, and 8 indicate that the presence of electrodes disturbs the brain activity very little, or at least, that the experimental conditions do not change during the period of observation.
64 citations
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