Organic electrode coatings for next-generation neural interfaces

Traditional neuronal interfaces utilize metallic electrodes which in recent years have reached a plateau in terms of the ability to provide safe stimulation at high resolution or rather with high densities of microelectrodes with improved spatial selectivity. To achieve higher resolution it has become clear that reducing the size of electrodes is required to enable higher electrode counts from the implant device. The limitations of interfacing electrodes including low charge injection limits, mechanical mismatch and foreign body response can be addressed through the use of organic electrode coatings which typically provide a softer, more roughened surface to enable both improved charge transfer and lower mechanical mismatch with neural tissue. Coating electrodes with conductive polymers or carbon nanotubes offers a substantial increase in charge transfer area compared to conventional platinum electrodes. These organic conductors provide safe electrical stimulation of tissue while avoiding undesirable chemical reactions and cell damage. However, the mechanical properties of conductive polymers are not ideal, as they are quite brittle. Hydrogel polymers present a versatile coating option for electrodes as they can be chemically modified to provide a soft and conductive scaffold. However, the in vivo chronic inflammatory response of these conductive hydrogels remains unknown. A more recent approach proposes tissue engineering the electrode interface through the use of encapsulated neurons within hydrogel coatings. This approach may provide a method for activating tissue at the cellular scale, however, several technological challenges must be addressed to demonstrate feasibility of this innovative idea. The review focuses on the various organic coatings which have been investigated to improve neural interface electrodes

Chronic multichannel neural recordings from soft regenerative microchannel electrodes during gait

Reliably interfacing a nerve with an electrode array is one of the approaches to restore motor and sensory functions after an injury to the peripheral nerve. Accomplishing this with current technologies is challenging as the electrode-neuron interface often degrades over time, and surrounding myoelectric signals contaminate the neuro-signals in awake, moving animals. The purpose of this study was to evaluate the potential of microchannel electrode implants to monitor over time and in freely moving animals, neural activity from regenerating nerves. We designed and fabricated implants with silicone rubber and elastic thin-film metallization. Each implant carries an eight-by-twelve matrix of parallel microchannels (of 120\u2009 7\u2009110\u2009\u3bcm2 cross-section and 4\u2009mm length) and gold thin-film electrodes embedded in the floor of ten of the microchannels. After sterilization, the soft, multi-lumen electrode implant is sutured between the stumps of the sciatic nerve. Over a period of three months and in four rats, the microchannel electrodes recorded spike activity from the regenerating sciatic nerve. Histology indicates mini-nerves formed of axons and supporting cells regenerate robustly in the implants. Analysis of the recorded spikes and gait kinematics over the ten-week period suggests firing patterns collected with the microchannel electrode implant can be associated with different phases of gait

Robust penetrating microelectrodes for neural interfaces realized by titanium micromachining

Neural prosthetic interfaces based upon penetrating microelectrode devices have broadened our understanding of the brain and have shown promise for restoring neurological functions lost to disease, stroke, or injury. However, the eventual viability of such devices for use in the treatment of neurological dysfunction may be ultimately constrained by the intrinsic brittleness of silicon, the material most commonly used for manufacture of penetrating microelectrodes. This brittleness creates predisposition for catastrophic fracture, which may adversely affect the reliability and safety of such devices, due to potential for fragmentation within the brain. Herein, we report the development of titanium-based penetrating microelectrodes that seek to address this potential future limitation. Titanium provides advantage relative to silicon due to its superior fracture toughness, which affords potential for creation of robust devices that are resistant to catastrophic failure. Realization of these devices is enabled by recently developed techniques which provide opportunity for fabrication of high-aspect-ratio micromechanical structures in bulk titanium substrates. Details are presented regarding the design, fabrication, mechanical testing, in vitro functional characterization, and preliminary in vivo testing of devices intended for acute recording in rat auditory cortex and thalamus, both independently and simultaneously

FMRP associates with cytoplasmic granules at the onset of meiosis in the human oocyte

Germ cell development and primordial follicle formation during fetal life is critical in establishing the pool of oocytes that subsequently determines the reproductive lifespan of women. Fragile X-associated primary ovarian insufficiency (FXPOI) is caused by inheritance of the FMR1 premutation allele and approximately 20% of women with the premutation allele develop ovarian dysfunction and premature ovarian insufficiency. However, the underlying disease mechanism remains obscure, and a potential role of FMRP in human ovarian development has not been explored. We have characterised the expression of FMR1 and FMRP in the human fetal ovary at the time of germ cell entry into meiosis through to primordial follicle formation. FMRP expression is exclusively in germ cells in the human fetal ovary. Increased FMRP expression in germ cells coincides with the loss of pluripotency-associated protein expression, and entry into meiosis is associated with FMRP granulation. In addition, we have uncovered FMRP association with components of P-bodies and stress granules, suggesting it may have a role in mRNA metabolism at the time of onset of meiosis. Therefore, this data support the hypothesis that FMRP plays a role regulating mRNAs during pivotal maturational processes in fetal germ cells, and ovarian dysfunction resulting from FMR1 premutation may have its origins during these stages of oocyte development

Fireflies in the night: Indigenous metaphor in Zapatista folktales

The intent of this comparative hermeneutic study is to examine how Subcomandante Marcos, spokesperson for the Zapatista Army of National Liberation (EZLN), expresses an indigenous worldview rooted in the Popol Vuh as a foundation for Zapatismo through the Viejo Antonio tales. The dissertation has two parts: the study itself and the English translations of the tales. The research is based upon the notion that folktales play a role in defining a people's culture and worldview, and that such texts create and maintain ethnic identity. It is also based upon Lakoff and Johnson's cognitive approach to metaphor which argues that metaphor influences one's perceptions of the world. The cognitive approach provides a rationale for understanding how indigenous oral stories and myth-histories furnish the metaphors that Subcomandante Marcos employs in the Viejo Antonio texts, called historias or "neo-myths" in this document, to impart an indigenous legitimacy to Zapatismo. The historias are classified as neo-indigenista literature, literature written to portray indigenous culture as a source of values that offer alternative perspectives for political and economic policy. Through Ricoeur's hermeneutic method employing distanciation and appropriation, this study extracts metaphors from the historias that are then compared to similar metaphors found in Tzotzil folktales and the Popol Vuh. The study shows that while Mayan narrative techniques and cultural references are found in the historias, most establish indigenous authority through the re-creation of themes and scenes in the Popol Vuh. Underlying these references are indigenous metaphors that describe the Zapatistas as both objects and actors embodying key Zapatista values. In particular, the Popol Vuh's theme of dawning, of light piercing the darkness, is used as a metaphor for the indigenous themselves in several historias. Through this metaphor, the indigenous are charged with the task of initiating and embodying a new world based upon the memory of the past. This study suggests that metaphorical analyses of the rhetoric of indigenous rights movements may illuminate connections to indigenous folktales and myth-histories that define a movement's objectives and participants. As in Ricoeur's methodology, the final section represents a personal experience of the texts as expanding one's personal horizons