The Use of Skeletal Muscle to Amplify Action Potentials in Transected Peripheral Nerves

Upper limb amputees suffer with problems associated with control and attachment of prostheses. Skin-surface electrodes placed over the stump, which detect myoelectric signals, are traditionally used to control hand movements. However, this method is unintuitive, the electrodes lift-off, and signal selectivity can be an issue. One solution to these limitations is to implant electrodes directly on muscles. Another approach is to implant electrodes directly into the nerves that innervate the muscles. A significant challenge with both solutions is the reliable transmission of biosignals across the skin barrier. In this thesis, I investigated the use of implantable muscle electrodes in an ovine model using myoelectrodes in combination with a bone-anchor, acting as a conduit for signal transmission. High-quality readings were obtained which were significantly better than skin-surface electrode readings. I further investigated the effect of electrode configurations to achieve the best signal quality. For direct recording from nerves, I tested the effect of adsorbed endoneural basement membrane proteins on nerve regeneration in vivo using microchannel neural interfaces implanted in rat sciatic nerves. Muscle and nerve signal recordings were obtained and improvements in sciatic nerve function were observed. Direct skeletal fixation of a prosthesis to the amputation stump using a bone-anchor has been proposed as a solution to skin problems associated with traditional socket-type prostheses. However, there remains a concern about the risk of infection between the implant and skin. Achieving a durable seal at this interface is therefore crucial, which formed the final part of the thesis. Bone-anchors were optimised for surface pore size and coatings to facilitate binding of human dermal fibroblasts to optimise skin-implant seal in an ovine model. Implants silanised with Arginine-Glycine-Aspartic Acid experienced significantly increased dermal tissue infiltration. This approach may therefore improve the soft tissue seal, and thus success of bone-anchored implants. By addressing both the way prostheses are attached to the amputation stump, by way of direct skeletal fixation, as well as providing high fidelity biosignals for high-level intuitive prosthetic control, I aim to further the field of limb loss rehabilitation

Topographic guidance scaffolds for peripheral nerve interfacing

In response to high and rising amputation rates, significant advances have been made in the field of prosthetic limb design. Unfortunately, there exists a lag in the neural interfacing technology required to provide an adequate link between the nervous system and this emerging generation of advanced prosthetic devices. Novel approaches to peripheral nerve interfacing are required to establish the stable, high channel count connections necessary to provide natural, thought driven control of an external prosthesis. Here, a tissue engineering-based approach has been used to create a device capable of interfacing with a regenerated portion of amputated nerve. As part of this work, a nerve guidance channel design, in which small amounts of interior scaffolding material could be precisely positioned, was evaluated. Guidance channels containing a single thin-film sheet of aligned scaffolding were shown to support robust functional nerve regeneration across extended injury gaps by minimally supplementing natural repair mechanisms. Significantly, these "thin-film enhanced nerve guidance channels" also provided the capability to guide the course of axons regenerating from a cut nerve. This capability to control axonal growth was next leveraged to create "regenerative scaffold electrodes (RSEs)" able to interface with axons regenerating from an amputated nerve. In the RSE design, low-profile arrays of interfacing electrodes were embedded within layers of aligned scaffolding material, such that regenerating axons were topographically guided by the scaffolding through the device and directly across the embedded electrodes. Chronically implanted RSEs were successfully used to record evoked neural activity from amputated nerves in an animal model. These results demonstrate that the use of topographic cues within a nerve guidance channel might offer the potential to influence the course of nerve regeneration to the advantage of a peripheral nerve interface suitable for limb amputees.PhDCommittee Chair: Ravi Bellamkonda; Committee Member: Arthur English; Committee Member: Pamela Bhatti; Committee Member: Robert Butera; Committee Member: Robert Le

Restoring Upper Extremity Mobility through Functional Neuromuscular Stimulation using Macro Sieve Electrodes

The last decade has seen the advent of brain computer interfaces able to extract precise motor intentions from cortical activity of human subjects. It is possible to convert captured motor intentions into movement through coordinated, artificially induced, neuromuscular stimulation using peripheral nerve interfaces. Our lab has developed and tested a new type of peripheral nerve electrode called the Macro-Sieve electrode which exhibits excellent chronic stability and recruitment selectivity. Work presented in this thesis uses computational modeling to study the interaction between Macro-Sieve electrodes and regenerated peripheral nerves. It provides a detailed understanding of how regenerated fibers, both on an individual level and on a population level respond differently to functional electrical stimulation compared to non-disrupted axons. Despite significant efforts devoted to developing novel regenerative peripheral interfaces, the degree of spatial clustering between functionally related fibers in regenerated nerves is poorly understood. In this thesis, bioelectrical modeling is also used to predict the degree of topographical organization in regenerated nerve trunks. In addition, theoretical limits of the recruitment selectivity of the device is explored and a set of optimal stimulation paradigms used to selectively activate fibers in different regions of the nerve are determined. Finally, the bioelectrical model of the interface/nerve is integrated with a biomechanical model of the macaque upper limb to study the feasibility of using macro-sieve electrodes to achieve upper limb mobilization

Conformable transistors for bioelectronics

The diversity of network disruptions that occur in patients with neuropsychiatric disorders creates a strong demand for personalized medicine. Such approaches often take the form of implantable bioelectronic devices that are capable of monitoring pathophysiological activity for identifying biomarkers to allow for local and responsive delivery of intervention. They are also required to transmit this data outside of the body for evaluation of the treatment’s efficacy. However, the ability to perform these demanding electronic functions in the complex physiological environment with minimum disruption to the biological tissue remains a big challenge. An optimal fully implantable bioelectronic device would require each component from the front-end to the data transmission to be conformable and biocompatible. For this reason, organic material-based conformable electronics are ideal candidates for components of bioelectronic circuits due to their inherent flexibility, and soft nature. In this work, first an organic mixed-conducting particulate composite material (MCP) able to form functional electronic components and non-invasively acquire high–spatiotemporal resolution electrophysiological signals by directly interfacing human skin is presented. Secondly, we introduce organic electrochemical internal ion-gated transistors (IGTs) as a high-density, high-amplification sensing component as well as a low leakage, high-speed processing unit. Finally, a novel wireless, battery-free strategy for electrophysiological signal acquisition, processing, and transmission that employs IGTs and an ionic communication circuit (IC) is introduced. We show that the wirelessly-powered IGTs are able to acquire and modulate neurophysiological data in-vivo and transmit them transdermally, eliminating the need for any hard Si-based electronics in the implant

Index to NASA tech briefs, 1971

The entries are listed by category, subject, author, originating source, source number/Tech Brief number, and Tech Brief number/source number. There are 528 entries

Sensorimotor content of multi-unit activity in the paramedian lobule of the cerebellum

Based on Center for Disease Control and Prevention report 2016, around 39.5 million people in the United States suffer from motor disabilities. These disabilities are due to traumatic conditions like traumatic brain injury (TBI), neurological diseases such as amyotrophic lateral sclerosis (ALS), or congenital conditions. One of the approaches for restoring the lost motor function is to extract the volitional information from the central nervous system (CNS) and control a mechanical device that can replace the function of a paralyzed limb through systems called Brain-Computer Interfaces (BCI). One of the major challenges being faced in BCIs and also in general neural recording field is the limitations of the microelectrodes. In this study, as the first aim, a custom-made micro-electrode array (MEA) using carbon fibers is developed. After ex vivo testing, they are implanted into the paramedian lobule (PML) of the rat cerebellum to record the multi-unit activity from its cortex. Following animal termination, tissue samples are examined with histological techniques for the assessment of tissue damage caused by the electrodes. Another challenge in the BCI field is extracting the control information regarding the intended motor function from the CNS. The way the cerebellar cortex encodes sensorimotor information and contributes to motor coordination has been a topic of discussion for decades. Recent studies have revealed high correlations between Purkinje cell simple spikes and the forelimb kinematics in experimental animals. However, tracking single spike activity in long-term implants with multi-channel electrodes has well-known challenges. Therefore, as the second aim of this study, the correlation of multi-unit neural signals from the paramedian lobule (PML) of the cerebellar cortex to the forelimb muscle activities (EMG) in rats during behavior was investigated. Linear regression is performed to predict the EMG signal envelopes using the cerebellar activity for various time shifts of the data (±10, ±50, ±100, and ±200 ms) to determine if the neural signals are primarily motor or sensory. The highest correlations (~0.6 on average) between neural and EMG envelopes are observed when the EMG signals are either shifted only about ±10 ms or not shifted at all with respect to the neural signals. There were however still correlations above the chance level for larger shifts in time. The results suggest that PML cortex contains both motor and sensory information in relation to the forelimb activity, and also that the extraction of motor information is feasible from multi-unit neural recordings from the cerebellar cortex. Increased prediction success was observed in reaching and retrieval phases compared to grasping phase when predictions were tested on three phases of the behavior separately. When EMG and neural signal envelopes were clustered, they showed patterns of surges of activity in all three phases. The neural signals showed higher activity in the reaching phase. The 300-1000Hz components of neural signals contributed to the predictions more than the other frequency bands. The results of this study supports the feasibility of a BCI based on MUA extracted from the cerebellar cortex using MEAs

Design and development of an implantable biohybrid device for muscle stimulation following lower motor neuron injury

In the absence of innervation caused by complete lower motor neuron injuries, skeletal muscle undergoes an inexorable course of degeneration and atrophy. The most apparent and debilitating clinical outcome of denervation is the immediate loss of voluntary use of muscle. However, these injuries are associated with secondary complications of bones, skin and cardiovascular system that, if untreated, may be fatal. Electrical stimulation has been implemented as a clinical rehabilitation technique in patients with denervated degenerated muscles offering remarkable improvements in muscle function. Nevertheless, this approach has limitations and side effects triggered by the delivery of high intensity electrical pulses. Combining innovative approaches in the fields of cell therapy and implanted electronics offers the opportunity to develop a biohybrid device to stimulate muscles in patients with lower motor neuron injuries. Incorporation of stem cell-derived motor neurons into implantable electrodes, could allow muscles to be stimulated in a physiological manner and circumvent problems associated with direct stimulation of muscle. The hypothesis underpinning this project is that artificially-grown motor neurons can serve as an intermediate between stimulator and muscle, converting the electrical stimulus into a biological action potential and re-innervating muscle via neuromuscular interaction. Here, a suitable stem cell candidate with therapeutic potential was identified and a differentiation protocol developed to generate motor neuron-like cells. Thick-film technology and laser micromachining were implemented to manufacture electrode arrays with features and dimensions suitable for implantation. Manufactured electrodes were electrochemically characterised, and motor neuron-like cells incorporated to create biohybrid devices. In vitro results indicate manufactured electrodes support motor neuron-like cell growth and neurite extension. Moreover, electrochemical characterisation suggests electrodes are suitable for stimulation. Preliminary in vivo testing explored implantation in a rat muscle denervation model. Overall, this thesis demonstrates initial development of a novel approach for fabricating biohybrid devices that may improve stimulation of denervated muscles

Implantable Electrodes for Upper Limb Prosthetic Control

This thesis describes a study investigating implantable interfaces with muscles and peripheral nerves. Current prostheses for upper limb amputees do not provide intuitive control over hand, wrist and elbow motion. By implanting electrodes for recording and stimulating onto muscles and into nerves in the amputation stump a greater number of control signals may be made available, signals which will be used to control dextrous hand movements. An implantable epimysial interface was developed using a bone-anchored device to hard-wire signals across the skin barrier. In a single ovine model pilot study the bone-anchor was implanted transtibially and the epimysial electrode was place superficially to m. peroneus teritus. Physiological signals were obtained over 12 weeks during treadmill walking. The external connector on the bone-anchor failed at 12 weeks, correlating with a drop in signal quality in an otherwise robust interface integrated with bone and skin tissue. The ovine bone-anchor model was repeated in 6 sheep for 19 weeks, with epimysial recordings made regularly. Increasing signal quality was seen during the study and was significantly greater from implanted electrodes compared with skin surface electrodes at 19 weeks (p = 0.016). Some complications with skin-implant integration were observed in proximally located implants. Crosstalk between muscles was assessed using pre-terminal nerve stimulation, and was found to be dependent upon muscle location and innervation. The ovine m. peroneus teritus model was used to assess recovery following targeted muscle reinnervation. Muscle signal recovery was observed approximately one month after surgery correlating with the start of functional recovery (assessed by force plate analysis). These studies indicate that a suitably modified bone-anchored device may be suitable for signal transmission in human patients, providing a stable, long-term solution to both prosthesis attachment and control. The potential of nerve interfaces for prosthetic control was investigated. The microchannel neural interface (MNI) was chosen because it overcomes limitations with other neural microarray designs: signal strength; cross-talk, and the locations of Nodes of Ranvier. MNIs confine regenerating nerves to small, ∼ 100 µm diameter, insulating tubes, this increases the length within which nerve signals can be recorded and amplifies the recorded signals. However, in vivo MNIs can become occluded by fibrosis that reduces or prevents axon regeneration. Two in vitro studies of neurocompatibility were carried out to investigate strategies for improving axon regeneration within microchannels. The first in vitro study compared the effect of different adsorbed endoneurial basement membrane proteins on PC-12 cell neurite extension on silicone substrates. The optimal protein coating concentrations for poly-D-lysine, collagen-IV and laminin-2,(-4) were determined. The optimal concentrations were compared with mixtures of basement membrane proteins, the effect of mixture coating order and constitution were investigated. It was found that endoneurial BM proteins significantly enhance neurite outgrowth compared with controls. Two coatings were suggested as most suited for improving neural regeneration within microchannels: a single layer coating of 10 µg/cm2 collagen-IV; and a mixed coating of 10 µg/cm2 collagen-IV, 1 µg/cm2 laminin-2,(-4), and 0.175 µg/cm2 nidogen-1. The second in vitro study investigated the effect of grooved, roughened and multi-scale silicone surfaces on on PC-12 cell neurite extension. Deeper, narrower grooves were shown to increase the extent of neurite alignment, while resulting in fewer, longer, neurites. Roughening surfaces was shown to increase the amount of protein (collagen-IV) which adsorbed from solution and increase the number of neurites each cell extended. Surfaces with multiscale topographies synergistically increased the number and length of neurites and guided neurite growth along the groove direction. MNIs were manufactured for in vivo testing. These MNIs were used to determine the effect of adsorbed endoneurial basement membrane proteins on nerve regeneration in vivo, but the multiscale topographies were not applied during manufacturing. Four alternative manufacturing methods were investigated and iterative improvements were made to create a stacked interface with multiple microchannel layers. Microchannel layers were created by laser patterning silicone and metal foil components, followed by plasma bonding to create a 3-dimensional structure with 150 µm deep, 200 µm wide microchannels. Electrode impedances of 27.2 ± 19.8 kΩ at 1kHz were achieved by DC etching. The method overcomes some current limitations on electrode connectivity and microchannel sealing, and may improve recording capabilities over single layer designs by increasing the ratio of electrodes to microchannels. Manufactured MNIs were tested in a rat sciatic nerve transection model. Following implantation nerves were allowed to regenerate for one and two months. First, suture and fibrin glue were compared as MNI fixation methods for one month, the nerve regenerated within the fibrin glue, outside the interface lumen, therefore sutures were chosen as a long term fixation method. The influence of endoneurial basement membrane protein coatings, identified previously, on nerve regeneration with MNIs was investigated. Nerves regenerated through the MNIs over two months and began to reinnervate the distal limb. Improvements in the sciatic function index were observed over two months, with no significant differences between protein coated and control interfaces. Some weak histological evidence for the use of protein coatings was found, with axon diameters increased distal to protein coated MNIs. Electromyographic and electroneurographic recordings demonstrated similar signal amplitudes to previous studies. In order to bring the research described in this thesis to clinical practice further engineering improvements to the design and manufacture of electrodes, which utilise materials or coatings to enhance neurocompatibility, is required. Avenues for further research are discussed and additional experiments and investigations are described. By combining developments in implantable muscle and nerve interfaces with surgical techniques and improvements in neurocompatibility the promise of upper limb prosthetic control may be realised