Materials and technologies for soft implantable neuroprostheses

Implantable neuroprostheses are engineered systems designed to restore or substitute function for individuals with neurological deficits or disabilities. These systems involve at least one uni-or bidirectional interface between a living neural tissue and a synthetic structure, through which information in the form of electrons, ions or photons flows. Despite a few notable exceptions, the clinical dissemination of implantable neuroprostheses remains limited, because many implants display inconsistent long-term stability and performance, and are ultimately rejected by the body. Intensive research is currently being conducted to untangle the complex interplay of failure mechanisms. In this Review, we emphasize the importance of minimizing the physical and mechanical mismatch between neural tissues and implantable interfaces. We explore possible materials solutions to design and manufacture neurointegrated prostheses, and outline their immense therapeutic potential

Epidural Stimulation Induced Modulation of Spinal Locomotor Networks in Adult Spinal Rats

The importance of the in vivo dynamic nature of the circuitries within the spinal cord that generate locomotion is becoming increasingly evident. We examined the characteristics of hindlimb EMG activity evoked in response to epidural stimulation at the S1 spinal cord segment in complete midthoracic spinal cord-transected rats at different stages of postlesion recovery. A progressive and phase-dependent modulation of monosynaptic (middle) and long-latency (late) stimulation-evoked EMG responses was observed throughout the step cycle. During the first 3 weeks after injury, the amplitude of the middle response was potentiated during the EMG bursts, whereas after 4 weeks, both the middle and late responses were phase-dependently modulated. The middle- and late-response magnitudes were closely linked to the amplitude and duration of the EMG bursts during locomotion facilitated by epidural stimulation. The optimum stimulation frequency that maintained consistent activity of the long-latency responses ranged from 40 to 60 Hz, whereas the short-latency responses were consistent from 5 to 130 Hz. These data demonstrate that both middle and late evoked potentials within a motor pool are strictly gated during in vivo bipedal stepping as a function of the general excitability of the motor pool and, thus, as a function of the phase of the step cycle. These data demonstrate that spinal cord epidural stimulation can facilitate locomotion in a time-dependent manner after lesion. The long-latency responses to epidural stimulation are correlated with the recovery of weight-bearing bipedal locomotion and may reflect activation of interneuronal central pattern-generating circuits

Undirected compensatory plasticity contributes to neuronal dysfunction after severe spinal cord injury

Severe spinal cord injury in humans leads to a progressive neuronal dysfunction in the chronic stage of the injury. This dysfunction is characterized by premature exhaustion of muscle activity during assisted locomotion, which is associated with the emergence of abnormal reflex responses. Here, we hypothesize that undirected compensatory plasticity within neural systems caudal to a severe spinal cord injury contributes to the development of neuronal dysfunction in the chronic stage of the injury. We evaluated alterations in functional, electrophysiological and neuromorphological properties of lumbosacral circuitries in adult rats with a staggered thoracic hemisection injury. In the chronic stage of the injury, rats exhibited significant neuronal dysfunction, which was characterized by co-activation of antagonistic muscles, exhaustion of locomotor muscle activity, and deterioration of electrochemically-enabled gait patterns. As observed in humans, neuronal dysfunction was associated with the emergence of abnormal, long-latency reflex responses in leg muscles. Analyses of circuit, fibre and synapse density in segments caudal to the spinal cord injury revealed an extensive, lamina-specific remodelling of neuronal networks in response to the interruption of supraspinal input. These plastic changes restored a near-normal level of synaptic input within denervated spinal segments in the chronic stage of injury. Syndromic analysis uncovered significant correlations between the development of neuronal dysfunction, emergence of abnormal reflexes, and anatomical remodelling of lumbosacral circuitries. Together, these results suggest that spinal neurons deprived of supraspinal input strive to re-establish their synaptic environment. However, this undirected compensatory plasticity forms aberrant neuronal circuits, which may engage inappropriate combinations of sensorimotor networks during gait executio

Differential effects of anti-Nogo-A antibody treatment and treadmill training in rats with incomplete spinal cord injury

Locomotor training on treadmills can improve recovery of stepping in spinal cord injured animals and patients. Likewise, lesioned rats treated with antibodies against the myelin associated neurite growth inhibitory protein, Nogo-A, showed increased regeneration, neuronal reorganization and behavioural improvements. A detailed kinematic analysis showed that the hindlimb kinematic patterns that developed in anti-Nogo-A antibody treated versus treadmill trained spinal cord injured rats were significantly different. The synchronous combined treatment group did not show synergistic effects. This lack of synergistic effects could not be explained by an increase in pain perception, sprouting of calcitonin gene-related peptide (CGRP) positive fibres or by interference of locomotor training with anti-Nogo-A antibody induced regeneration and sprouting of descending fibre tracts. The differential mechanisms leading to behavioural recovery during task-specific training and in regeneration or plasticity enhancing therapies have to be taken into account in designing combinatorial therapies so that their potential positive interactive effects can be fully expresse

A neurorobotic platform for locomotor prosthetic development in rats and mice

Objectives. We aimed to develop a robotic interface capable of providing finely-tuned, multidirectional trunk assistance adjusted in real-time during unconstrained locomotion in rats and mice. Approach. We interfaced a large-scale robotic structure actuated in four degrees of freedom to exchangeable attachment modules exhibiting selective compliance along distinct directions. This combination allowed high-precision force and torque control in multiple directions over a large workspace. We next designed a neurorobotic platform wherein real-time kinematics and physiological signals directly adjust robotic actuation and prosthetic actions. We tested the performance of this platform in both rats and mice with spinal cord injury. Main Results. Kinematic analyses showed that the robotic interface did not impede locomotor movements of lightweight mice that walked freely along paths with changing directions and height profiles. Personalized trunk assistance instantly enabled coordinated locomotion in mice and rats with severe hindlimb motor deficits. Closed-loop control of robotic actuation based on ongoing movement features enabled real-time control of electromyographic activity in anti-gravity muscles during locomotion. Significance. This neurorobotic platform will support the study of the mechanisms underlying the therapeutic effects of locomotor prosthetics and rehabilitation using high-resolution genetic tools in rodent models

Training locomotor networks

For a complete adult spinal rat to regain some weight-bearing stepping capability, it appears that a sequence of specific proprioceptive inputs that are similar, but not identical, from step to step must be generated over repetitive step cycles. Furthermore, these cycles must include the activation of specific neural circuits that are intrinsic to the lumbosacral spinal cord segments. For these sensorimotor pathways to be effective in generating stepping, the spinal circuitry must be modulated to an appropriate excitability level. This level of modulation is sustained from supraspinal input in intact, but not spinal, rats. In a series of experiments with complete spinal rats, we have shown that an appropriate level of excitability of the spinal circuitry can be achieved using widely different means. For example, this modulation level can be acquired pharmacologically, via epidural electrical stimulation over specific lumbosacral spinal cord segments, and/or by use-dependent mechanisms such as step or stand training. Evidence as to how each of these treatments can “tune” the spinal circuitry to a “physiological state” that enables it to respond appropriately to proprioceptive input will be presented. We have found that each of these interventions can enable the proprioceptive input to actually control extensive details that define the dynamics of stepping over a range of speeds, loads, and directions. A series of experiments will be described that illustrate sensory control of stepping and standing after a spinal cord injury and the necessity for the “physiological state” of the spinal circuitry to be modulated within a critical window of excitability for this control to be manifested. The present findings have important consequences not only for our understanding of how the motor pattern for stepping is formed, but also for the design of rehabilitation intervention to restore lumbosacral circuit function in humans following a spinal cord injury

Evaluating Nutraceuticals for Selective Toxicity Toward Leukemia Stem Cells

Targeting leukemia stem cells (LSCs) is critical to improving the poor outcome of acute myeloid leukemia (AML) patients. Nutraceuticals (i.e., food derived bioactive compounds) provide a wealthy resource for novel anti-cancer, and specifically anti-AML drug discovery. With the advent of novel LSC cell lines, preliminary screening of these compounds against LSC-like cells can be achieved rapidly. To identify potential novel anti-LSC therapeutics, we created and screened a unique library consisting of 288 nutraceuticals in an MTS assay against TEX leukemia cells, a surrogate LSC line and K562, a control cell line which does not possess LSC activity. Here, we identified diosmetin, a flavonoid found in citrus fruits and various green plants, as a novel anti- LSC agent (EC50: 6.0 ± 1.7μM). To confirm its activity, diosmetin (10μM) reduced clonogenic growth of primary AML cells (n = 4) with no effect on normal CD34 positive bone marrow derived stem cells (n = 3) observed in colony forming cell assays. A dose-response and time course analysis performed via the Annexin/PI assay and flow cytometry revealed that diosmetin induced apoptosis, as evidenced by the accumulation of ANN+/PI- cells. Apoptosis was further confirmed by a subG1 peak after performing cell cycle analysis. Utilizing the Database for Annotation, Visualization and Integrated Discovery (DAVID) tool, we determined that the estrogen receptor (ER) was a potential molecular target for diosmetin’s anti-leukemia activity. To assess the role of estrogen receptors, we measured ERα and ERβ protein levels in diosmetin sensitive and insensitive cell lines. Interestingly, diosmetin sensitive cell lines display significantly elevated ERβ protein levels compared to diosmetin insensitive cells. However, this pattern was not observed for ERα. Similar results were observed through quantitative PCR measures, as TEX cells displayed levels of ESR2 (ERβ) mRNA, with no observed levels of ESR1 (ERα) mRNA levels. The opposite results were observed in K562 cells. Through ER reporter assays, it was demonstrated that diosmetin acts as a partial agonist in ERβ reporter cells, increasing luciferase activity with increasing doses of diosmetin in ERβ reporter cells. Moreover, we find that caspase 8 but not caspase 9 is elevated following diosmetin treatment, consistent with the extrinsic pathway of apoptosis and our observed increased in TNF-α, similar to previous reports highlighting the link between ERβ agonists and cancer cell death. In summary, these studies highlight that estrogen receptors, specifically ERβ, is a novel LSC therapeutic target, and the potential role of nutraceuticals as promising compounds for future drug discovery endeavours

Wireless Neurosensor for Full-Spectrum Electrophysiology Recordings during Free Behavior

SummaryBrain recordings in large animal models and humans typically rely on a tethered connection, which has restricted the spectrum of accessible experimental and clinical applications. To overcome this limitation, we have engineered a compact, lightweight, high data rate wireless neurosensor capable of recording the full spectrum of electrophysiological signals from the cortex of mobile subjects. The wireless communication system exploits a spatially distributed network of synchronized receivers that is scalable to hundreds of channels and vast environments. To demonstrate the versatility of our wireless neurosensor, we monitored cortical neuron populations in freely behaving nonhuman primates during natural locomotion and sleep-wake transitions in ecologically equivalent settings. The interface is electrically safe and compatible with the majority of existing neural probes, which may support previously inaccessible experimental and clinical research

Rehabilitative Soft Exoskeleton for Rodents

Robotic exoskeletons provide programmable, consistent and controllable active therapeutic assistance to patients with neurological disorders. Here we introduce a prototype and preliminary experimental evaluation of a rehabilitative gait exoskeleton that enables compliant yet effective manipulation of the fragile limbs of rats. To assist the displacements of the lower limbs without impeding natural gait movements, we designed and fabricated soft pneumatic actuators (SPAs). The exoskeleton integrates two customizable SPAs that are attached to a limb. This configuration enables a 1 N force load, a range of motion exceeding 80 mm in the major axis, and speed of actuation reaching two gait cycles/s. Preliminary experiments in rats with spinal cord injury validated the basic features of the exoskeleton. We propose strategies to improve the performance of the robot and discuss the potential of SPAs for the design of other wearable interfaces