Improving the Selectivity of an Osseointegrated Neural Interface: Proof of Concept For Housing Sieve Electrode Arrays in the Medullary Canal of Long Bones.

Sieve electrodes stand poised to deliver the selectivity required for driving advanced prosthetics but are considered inherently invasive and lack the stability required for a chronic solution. This proof of concept experiment investigates the potential for the housing and engagement of a sieve electrode within the medullary canal as part of an osseointegrated neural interface (ONI) for greater selectivity toward improving prosthetic control. The working hypotheses are that (A) the addition of a sieve interface to a cuff electrode housed within the medullary canal of the femur as part of an ONI would be capable of measuring efferent and afferent compound nerve action potentials (CNAPs) through a greater number of channels; (B) that signaling improves over time; and (C) that stimulation at this interface generates measurable cortical somatosensory evoked potentials through a greater number of channels. The modified ONI was tested in a rabbit (n = 1) amputation model over 12 weeks, comparing the sieve component to the cuff, and subsequently compared to historical data. Efferent CNAPs were successfully recorded from the sieve demonstrating physiological improvements in CNAPs between weeks 3 and 5, and somatosensory cortical responses recorded at 12 weeks postoperatively. This demonstrates that sieve electrodes can be housed and function within the medullary canal, demonstrated by improved nerve engagement and distinct cortical sensory feedback. This data presents the conceptual framework for housing more sophisticated sieve electrodes in bone as part of an ONI for improving selectivity with percutaneous connectivity toward improved prosthetic control.

Experimental Basis for Creating an Osseointegrated Neural Interface for Prosthetic Control: A Pilot Study in Rabbits.

INTRODUCTION: While debate persists over how to best prevent or treat amputation neuromas, the more pressing question of how to best marry residual nerves to state-of-the-art robotic prostheses for naturalistic control of a replacement limb has come to the fore. One potential solution involves the transposition of terminal nerve ends into the medullary canal of long bones, creating the neural interface within the bone. Nerve transposition into bone is a long-practiced, clinically relevant treatment for painful neuromas. Despite neuropathic pain relief, the physiological capacity of transposed nerves to conduct motor and sensory signals required for prosthesis control remains unknown. This pilot study addresses the hypotheses that (1) bone provides stability to transposed nerves and (2) nerves transposed into bone remain physiologically active, as they relate to the creation of an osseointegrated neural interface. METHODS: New Zealand white rabbits received transfemoral amputation, with the sciatic nerve transposed into the femur. RESULTS: Morphological examination demonstrates that nerves remain stable within the medullary canal, while compound nerve action potentials evoked by electrical stimulation of the residual nerve within the bone could be achieved at 12 weeks (p < 0.0005). CONCLUSION: Transposed nerves retain a degree of physiological function suitable for creating an osseointegrated neural interface.

Methodology for creating a chronic osseointegrated neural interface for prosthetic control in rabbits.

BACKGROUND: Chronic stability and high degrees of selectivity are both essential but somewhat juxtaposed components for creating an implantable bi-directional PNI capable of controlling of a prosthetic limb. While the more invasive implantable electrode arrays provide greater specificity, they are less stable over time due to compliance mismatch with the dynamic soft tissue environment in which the interface is created. NEW METHOD: This paper takes the surgical approach of transposing nerves into bone to create neural interface within the medullary canal of long bones, an osseointegrated neural interface, to provide greater stability for implantable electrodes. In this context, we describe the surgical model for transfemoral amputation with transposition of the sciatic nerve into the medullary canal in rabbits. We investigate the capacity to create a neural interface within the medullary canal histolomorphologically. In a separate proof of concept experiment, we quantify the chronic physiological capacity of transposed nerves to conduct compound nerve action potentials evoked via an Osseointegrated Neural Interface. COMPARISON WITH EXISTING METHOD(S): The rabbit serves as an important animal model for both amputation neuroma and osseointegration research, but is underutilized for the exploration neural interfacing in an amputation setting. RESULTS: Our findings demonstrate that transposed nerves remain stable over 12 weeks. Creating a neural interface within the medullary canal is possible and does not impede nerve regeneration or physiological capacity. CONCLUSIONS: This article represents the first evidence that an Osseointegrated Neural Interface can be surgically created, capable of chronic stimulation/recording from amputated nerves required for future prosthetic control.

µECoG Recordings Through a Thinned Skull.

The studies described in this paper for the first time characterize the acute and chronic performance of optically transparent thin-film micro-electrocorticography (µECoG) grids implanted on a thinned skull as both an electrophysiological complement to existing thinned skull preparation for optical recordings/manipulations, and a less invasive alternative to epidural or subdurally placed µECoG arrays. In a longitudinal chronic study, µECoG grids placed on top of a thinned skull maintain impedances comparable to epidurally placed µECoG grids that are stable for periods of at least 1 month. Optogenetic activation of cortex is also reliably demonstrated through the optically transparent µECoG grids acutely placed on the thinned skull. Finally, spatially distinct electrophysiological recordings were evident on µECoG electrodes placed on a thinned skull separated by 500-750 µm, as assessed by stimulation evoked responses using optogenetic activation of cortex as well as invasive and epidermal stimulation of the sciatic and median nerve at chronic time points. Neural signals were collected through a thinned skull in mice and rats, demonstrating potential utility in neuroscience research applications such as in vivo imaging and optogenetics.

Flexible, multichannel cuff electrode for selective electrical stimulation of the mouse trigeminal nerve.

The trigeminal nerve (cranial nerve V), along with other cranial nerves, has in recent years become a popular target for bioelectric medicine due to its direct access to neuromodulatory centers. Trigeminal nerve stimulation is currently being evaluated as an adjunctive treatment for various neurodegenerative and neuropsychiatric diseases despite the mechanism of action being in question. In this work, we describe the development and validation of a novel neural interface for the infraorbital branch of the trigeminal nerve utilizing a thin film (TF) nerve cuff containing multiple electrode sites allowing for more selective stimulation of the nerve. We characterized the properties of the device using electrochemical impedance spectroscopy, cyclic voltammetry, voltage excursions, and in vivo testing. Electrochemical measurements demonstrate that the platinum-based electrodes possess a capacitive charge carrying mechanism suitable for stimulation of biological tissue with a safe charge injection limit of 73.13 µC/cm2. In vivo stimulation experiments show that the TF cuff can reliably stimulate nerve targets eliciting cortical responses similar to a silicone cuff electrode. Furthermore, selecting different pairs of stimulation electrodes on the TF cuff modulated the magnitude and/or spatial pattern of cortical responses suggesting that the device may be able to selectively stimulate different parts of the nerve. These results suggest that the TF cuff is a viable neural interface for stimulation of the infraorbital branch of the trigeminal nerve that enables future research examining the therapeutic mechanisms of trigeminal nerve stimulation.

Progress in the Field of Micro-Electrocorticography.

Since the 1940s electrocorticography (ECoG) devices and, more recently, in the last decade, micro-electrocorticography (µECoG) cortical electrode arrays were used for a wide set of experimental and clinical applications, such as epilepsy localization and brain⁻computer interface (BCI) technologies. Miniaturized implantable µECoG devices have the advantage of providing greater-density neural signal acquisition and stimulation capabilities in a minimally invasive fashion. An increased spatial resolution of the µECoG array will be useful for greater specificity diagnosis and treatment of neuronal diseases and the advancement of basic neuroscience and BCI research. In this review, recent achievements of ECoG and µECoG are discussed. The electrode configurations and varying material choices used to design µECoG arrays are discussed, including advantages and disadvantages of µECoG technology compared to electroencephalography (EEG), ECoG, and intracortical electrode arrays. Electrode materials that are the primary focus include platinum, iridium oxide, poly(3,4-ethylenedioxythiophene) (PEDOT), indium tin oxide (ITO), and graphene. We discuss the biological immune response to µECoG devices compared to other electrode array types, the role of µECoG in clinical pathology, and brain⁻computer interface technology. The information presented in this review will be helpful to understand the current status, organize available knowledge, and guide future clinical and research applications of µECoG technologies.

Characterizing cortical responses evoked by electrical stimulation of the mouse infraorbital nerve.

In recent years, the trigeminal nerve (CN V) has become a popular target for neuromodulation therapies to treat of a variety of diseases due to its access to neuromodulatory centers. Despite promising preclinical and clinical data, the mechanism of action of trigeminal nerve stimulation (TNS) remains in question. In this work, we describe the development and evaluation of a neural interface targeting the mouse trigeminal nerve with the goal of enabling future mechanistic research on TNS. We performed experiments designed to evaluate the ability of a peripheral nerve interface (i.e. cuff electrode) to stimulate the infraorbital branch of the trigeminal nerve. We found that both artificial and naturalistic stimulation of the trigeminal nerve elicited robust cortical responses in the somatosensory cortex that scaled with increases in stimulus amplitude. These results suggest that an infraorbital nerve interface is a suitable candidate for examining the neural mechanisms of TNS in the mouse.

Single-neuronal cell culture and monitoring platform using a fully transparent microfluidic DEP device.

Dielectrophoresis using multi-electrode arrays allows a non-invasive interface with biological cells for long-term monitoring of electrophysiological parameters as well as a label-free and non-destructive technique for neuronal cell manipulation. However, experiments for neuronal cell manipulation utilizing dielectrophoresis have been constrained because dielectrophoresis devices generally function outside of the controlled environment (i.e. incubator) during the cell manipulation process, which is problematic because neurons are highly susceptible to the properties of the physiochemical environment. Furthermore, the conventional multi-electrode arrays designed to generate dielectrophoretic force are often fabricated with non-transparent materials that confound live-cell imaging. Here we present an advanced single-neuronal cell culture and monitoring platform using a fully transparent microfluidic dielectrophoresis device for the unabated monitoring of neuronal cell development and function. The device is mounted inside a sealed incubation chamber to ensure improved homeostatic conditions and reduced contamination risk. Consequently, we successfully trap and culture single neurons on a desired location and monitor their growth process over a week. The proposed single-neuronal cell culture and monitoring platform not only has significant potential to realize an in vitro ordered neuronal network, but also offers a useful tool for a wide range of neurological research and electrophysiological studies of neuronal networks.

Optogenetic interrogation of neurovascular coupling in the cerebral cortex of transgenic mice.

OBJECTIVE: We introduce an engineering approach to study spatiotemporal correlations between vasodynamics and the nearby neural activity in open-loop and closed-loop paradigms. APPROACH: We integrated optogenetic technology with optical coherence tomography to apply spatiotemporal patterns of optical neurostimulation to the cortex of transgenic optogenetic mice and measure blood flow-rate, velocity, and diameter changes of selected middle cerebral artery branches. MAIN RESULTS: The spatiotemporal characteristics of blood flow-rate, velocity, and vessel diameter responses to localized neurostimulation light pulses were measured. It was observed that the location of stimulation relative to the surrounding vascular topology had notable effects on temporal patterns of vasodynamic responses. This effect was studied by creating velocity, flow-rate, and diameter sensitivity maps for selected arteries. Generally, neural stimulation in the vicinity of downstream capillaries of an artery evoked a fast transient increase in the blood flow-rate, velocity, and vessel diameter which was followed by a long-lasting secondary peak-response. The temporal span of the flow-rate response was quasi-linearly proportional to the length of stimulation. When neural stimulation was delivered to the area in the vicinity of one daughter branch of an artery, in other branches, we observed some drop in blood velocity and/or flow-rate and concurring increase of the vessel diameter. To examine the reliability of the coupling between neural activity and regional blood flow, a closed-loop feedback controller was implemented which is capable of maintaining blood flow-rate at any desired level for relatively longer periods by continuously adjusting the width of stimulation pulses. SIGNIFICANCE: The proposed approach opens new lines of research with potential applications in understanding the role of different cell types in the cerebrovascular regulatory mechanisms and the study of the adaptive process of angiogenesis in the cerebral cortex. The observation of incoherent responses of vessel diameter, blood flow-rate, and velocity suggests that such detailed information is necessary to obtain an accurate interpretation of the data acquired via hemodynamic based functional imaging techniques.

Neuroma Implantation into Long Bones: Clinical Foundation for a Novel Osseointegrated Peripheral Nerve Interface.

Symptomatic neuroma after major extremity amputation is a challenging clinical problem for which there are many described treatment options. Neuroma excision and implantation into the medullary canal of long bones offers durability and insulation, and minimizes chronic pain. Another challenge in amputees is impaired function and an ongoing need for accessible and functional prostheses that are "bidirectional," in that they provide both fine motor control and sensory feedback. Drawing on clinical experience with neuroma implantation into the medullary canal of long bones, the authors propose a novel neural interface whereby a terminal nerve end is redirected into the medullary canal of a nearby long bone and interfaced with an electrode array. The osseointegrated neural interface aims to exploit electrical signals from peripheral nerves to control advanced prosthetic devices for amputees. The purpose of this article is to present 2 clinical cases of nerve translocation into bone that serve as the clinical foundation of the osseointegrated neural interface as an innovative interface for prosthetic control.

Electrical Neural Stimulation and Simultaneous in Vivo Monitoring with Transparent Graphene Electrode Arrays Implanted in GCaMP6f Mice.

Electrical stimulation using implantable electrodes is widely used to treat various neuronal disorders such as Parkinson's disease and epilepsy and is a widely used research tool in neuroscience studies. However, to date, devices that help better understand the mechanisms of electrical stimulation in neural tissues have been limited to opaque neural electrodes. Imaging spatiotemporal neural responses to electrical stimulation with minimal artifact could allow for various studies that are impossible with existing opaque electrodes. Here, we demonstrate electrical brain stimulation and simultaneous optical monitoring of the underlying neural tissues using carbon-based, fully transparent graphene electrodes implanted in GCaMP6f mice. Fluorescence imaging of neural activity for varying electrical stimulation parameters was conducted with minimal image artifact through transparent graphene electrodes. In addition, full-field imaging of electrical stimulation verified more efficient neural activation with cathode leading stimulation compared to anode leading stimulation. We have characterized the charge density limitation of capacitive four-layer graphene electrodes as 116.07-174.10 µC/cm2 based on electrochemical impedance spectroscopy, cyclic voltammetry, failure bench testing, and in vivo testing. This study demonstrates the transparent ability of graphene neural electrodes and provides a method to further increase understanding and potentially improve therapeutic electrical stimulation in the central and peripheral nervous systems.

Quantification of Collagen Organization after Nerve Repair.

BACKGROUND: Clinical outcomes after nerve injury and repair remain suboptimal. Patients may be plagued by poor functional recovery and painful neuroma at the repair site, characterized by disorganized collagen and sprouting axons. Collagen deposition during wound healing can be intrinsically imaged using second harmonic generation (SHG) microscopy. The purpose of this study was to develop a protocol for SHG imaging of nerves and to assess whether collagen alignment can be quantified after nerve repair. METHODS: Sciatic nerve transection and epineural repair was performed in male rats. The contralateral nerves were used as intra-animal controls. Ten-millimeter nerve segments were harvested and fixed onto slides. SHG images were collected using a 20× objective on a multiphoton microscope. Collagen fiber alignment was calculated using CurveAlign software. Alignment was calculated on a scale from 0 to 1, where 1 represents perfect alignment. Statistical analysis was performed using a linear mixed-effects model. RESULTS: Eight male rats underwent right sciatic nerve repair using 9-0 Nylon suture. There were gross variations in collagen fiber organization in the repaired nerves compared with the controls. Quantitatively, collagen fibers were more aligned in the control nerves (mean alignment 0.754, SE 0.055) than in the repairs (mean alignment 0.413, SE 0.047; P < 0.001). CONCLUSIONS: SHG microscopy can be used to quantitate collagen after nerve repair via fiber alignment. Given that the development of neuroma likely reflects aberrant wound healing, ex vivo and/or in vivo SHG imaging may be useful for further investigation of the variables predisposing to neuroma.

Fabrication and utility of a transparent graphene neural electrode array for electrophysiology, in vivo imaging, and optogenetics.

Transparent graphene-based neural electrode arrays provide unique opportunities for simultaneous investigation of electrophysiology, various neural imaging modalities, and optogenetics. Graphene electrodes have previously demonstrated greater broad-wavelength transmittance (∼90%) than other transparent materials such as indium tin oxide (∼80%) and ultrathin metals (∼60%). This protocol describes how to fabricate and implant a graphene-based microelectrocorticography (µECoG) electrode array and subsequently use this alongside electrophysiology, fluorescence microscopy, optical coherence tomography (OCT), and optogenetics. Further applications, such as transparent penetrating electrode arrays, multi-electrode electroretinography, and electromyography, are also viable with this technology. The procedures described herein, from the material characterization methods to the optogenetic experiments, can be completed within 3-4 weeks by an experienced graduate student. These protocols should help to expand the boundaries of neurophysiological experimentation, enabling analytical methods that were previously unachievable using opaque metal-based electrode arrays.

Una tabla salvavidas para los padres / A lifesaver table for parents

El mejor tiempo para planificar la estrategia referente a la crianza de los niños, es antes de que el primer hijo nazca. ¿Cuál es el propósito de traer niños al mundo? ¿Cuáles son los valores éticos y educativos para los padres? ¿Cuál será su relación con los niños? ¿Cómo se comunicarán? ¿Cómo serán disciplinados? Estas y muchas otras preguntas deberían ser hechas por los que van a ser padres. ¿Qué pasaría si la pareja descubre algunas diferencias básicas en la educación de los hijos? ¿Será mejor descubrirlas a tiempo y antes que produzcan una crisis matrimonial posterior? Aunque no es necesario que ambos padres estén de acuerdo en el 100% de las veces, es crucial conocer estas diferencias y resolverlas cooperativamente. En efecto, los niños que crecen en un hogar donde papá y mamá están comprometidos uno con el otro, están aprendiendo una experiencia importante en la vida. A continuación, el psiquiatra infantil norteamericano, Joseph R. Novello, Profesor en la Universidad de Georgetown, Washinton D.C., contestará, en forma sencilla, las principales preguntas que los padres habitualmente plantean al médico y que suelen ser una fuente de conflictos conyugales, y que todo pediatra debe saber su respuesta

Tabla salvavidas para los padres / Lifesaver table for parents

El mejor tiempo para planificar la estrategia referente a la crianza de los niños, es antes de que el primer hijo nazca. ¿Cuál es el propósito de traer niños al mundo? ¿Cuáles son los valores éticos y educativos de los padres? ¿Cuál será su relación con los niños? ¿Cómo se comunicarán? ¿Cómo serán disciplinados? Estas y muchas otras preguntas deberían ser hechas por los que van a ser padres. ¿Qué pasaría si la pareja descubre algunas diferencias básicas en la educación de los hijos? Será mejor descubrirlas a tiempo y antes que produzcan una crisis matrimonial posterior. Aunque no es necesario que ambos padres estén de acuerdo en el 100% de las veces, es crucial conocer estas diferencias y resolverlas cooperativamente. En efecto, los niños que crecen en un hogar donde papá y mamá están comprometidos uno con el otro, están aprendiendo una experiencia importante en la vida. A continuación el psiquiatra infantil norteamericano Joseph R. Novello, Profesor en la Universidad de Georgetown, Washington D.C., contestará en forma sencilla las principales preguntas que los padres habitualmente plantean al médico y que suelen ser una fuente de conflictos conyugales, y que todo pediatra debe saber su respuesta

Una tabla salvavidas para los padres / A lifesaves table for the parents

El mejor tiempo para planificar la estrategia referente a la crianza de los niños, es antes de que el primer hijo nazca. ¿Cual es el propósito de traer niños al mundo? ¿Cuáles son los valores éticos y educativos de los padres? ¿Cual será su relación con los niños? ¿Cómo se comunicarán? ¿Cómo serán disciplinados? Estas y muchas otras preguntas deberían ser hechas por los que van a ser padres. ¿Qué pasaría si la pareja descubre algunas diferencias básicas en la educación de los hijos? Será mejor descubrirlas a tiempo y antes que produzcan una crisis matrimonial posterior. Aunque no es necesario que ambos padres estén de acuerdo en el 100% de las veces, es crucial conocer estas diferencias y resolverlas cooperativamente. En efecto, los niños que crecen en un hogar donde papá y mamá están comprometidos uno con el otro, están aprendiendo una experiencia importante en la vida. A continuación el psiquiatra infantil norteamericano Joseph R. Novello, Profesor en la Universidad de Georgetown, Washington D.C., contestará en forma sencilla las principales preguntas que los padres habitualmente plantean al médico y que suelen ser una fuente de conflictos conyugales, y que todo pediatra debe saber su respuesta.