Blood brain barrier (BBB)-disruption in intracortical silicon microelectrode implants

Comprehensive proteomic analysis of the differential expression of 62 proteins following intracortical microelectrode implantation

Intracortical microelectrodes (IMEs) are devices designed to be implanted into the cerebral cortex for various neuroscience and neuro-engineering applications. A critical feature of IMEs is their ability to detect neural activity from individual neurons. Currently, IMEs are limited by chronic failure, largely considered to be caused by the prolonged neuroinflammatory response to the implanted devices. Over the past few years, the characterization of the neuroinflammatory response has grown in sophistication, with the most recent advances focusing on mRNA expression following IME implantation. While gene expression studies increase our broad understanding of the relationship between IMEs and cortical tissue, advanced proteomic techniques have not been reported. Proteomic evaluation is necessary to describe the diverse changes in protein expression specific to neuroinflammation, neurodegeneration, or tissue and cellular viability, which could lead to the further development of targeted intervention strategies designed to improve IME functionality. In this study, we have characterized the expression of 62 proteins within 180 μm of the IME implant site at 4-, 8-, and 16-weeks post-implantation. We identified potential targets for immunotherapies, as well as key pathways that contribute to neuronal dieback around the IME implant.

Advanced age is not a barrier to chronic intracortical single-unit recording in rat cortex

Introduction

Available evidence suggests that as we age, our brain and immune system undergo changes that increase our susceptibility to injury, inflammation, and neurodegeneration. Since a significant portion of the potential patients treated with a microelectrode-based implant may be older, it is important to understand the recording performance of such devices in an aged population.

Methods

We studied the chronic recording performance and the foreign body response (FBR) to a clinically used microelectrode array implanted in the cortex of 18-month-old Sprague Dawley rats.

Results and discussion

To the best of our knowledge, this is the first preclinical study of its type in the older mammalian brain. Here, we show that single-unit recording performance was initially robust then gradually declined over a 12-week period, similar to what has been previously reported using younger adult rats and in clinical trials. In addition, we show that FBR biomarker distribution was similar to what has been previously described for younger adult rats implanted with multi-shank recording arrays in the motor cortex. Using a quantitative immunohistochemcal approach, we observed that the extent of astrogliosis and tissue loss near the recording zone was inversely related to recording performance. A comparison of recording performance with a younger cohort supports the notion that aging, in and of itself, is not a limiting factor for the clinical use of penetrating microelectrode recording arrays for the treatment of certain CNS disorders.

Receptor-Assisted Nanotherapeutics for Overcoming the Blood-Brain Barrier

Blood-brain barrier (BBB) is a distinguishing checkpoint that segregates peripheral organs from neural compartment. It protects the central nervous system from harmful ambush of antigens and pathogens. Owing to such explicit selectivity, the BBB hinders passage of various neuroprotective drug molecules that escalates into poor attainability of neuroprotective agents towards the brain. However, few molecules can surpass the BBB and gain access in the brain parenchyma by exploiting surface transporters and receptors. For successful development of brain-targeted therapy, understanding of BBB transporters and receptors is crucial. This review focuses on the transporter and receptor-based mechanistic pathway that can be manoeuvred for better comprehension of reciprocity of receptors and nanotechnological vehicle delivery. Nanotechnology has emerged as one of the expedient noninvasive approaches for brain targeting via manipulating the hurdle of the BBB. Various nanovehicles are being reported for brain-targeted delivery such as nanoparticles, nanocrystals, nanoemulsion, nanolipid carriers, liposomes and other nanovesicles. Nanotechnology-aided brain targeting can be a strategic approach to circumvent the BBB without altering the inherent nature of the BBB.

Insertional effect following electrode implantation: an underreported but important phenomenon

Deep brain stimulation has revolutionized the treatment of movement disorders and is gaining momentum in the treatment of several other neuropsychiatric disorders. In almost all applications of this therapy, the insertion of electrodes into the target has been shown to induce some degree of clinical improvement prior to stimulation onset. Disregarding this phenomenon, commonly referred to as 'insertional effect', can lead to biased results in clinical trials, as patients receiving sham stimulation may still experience some degree of symptom amelioration. Similar to the clinical scenario, an improvement in behavioural performance following electrode implantation has also been reported in preclinical models. From a neurohistopathologic perspective, the insertion of electrodes into the brain causes an initial trauma and inflammatory response, the activation of astrocytes, a focal release of gliotransmitters, the hyperexcitability of neurons in the vicinity of the implants, as well as neuroplastic and circuitry changes at a distance from the target. Taken together, it would appear that electrode insertion is not an inert process, but rather triggers a cascade of biological processes, and, as such, should be considered alongside the active delivery of stimulation as an active part of the deep brain stimulation therapy.

Exosome Heterogeneity Affects the Distal "Barrier-Crossing" Trafficking of Exosome Encapsulated Quantum Dots

The biological activities of nanoparticles (NPs), which include endocytosis by macrophages and subsequent intracellular degradation and/or release, transfer to other cells, or translocation across tissue barriers, highly depend on their fate in living organisms. Yet, translocation across barriers, especially the distal "barrier-crossing" trafficking of NPs, is still unclear. The exosome (Exo) plays a crucial role in intercellular communication and biological barrier trafficking. Here, we report that ZnCdSe@ZnS quantum dots (QDs), as a representation of NPs in biomedical applications, could cross the blood-brain barrier and approach the mouse brain via active Exo encapsulation. By employing multiple techniques, we demonstrated that QDs were internalized by macrophages (J774A.1) and tumor cells (HeLa) and then released to the extracellular environment along with Exo. Exo encapsulation facilitates the distal barrier-crossing trafficking of QDs in vivo, while Exo biogenesis inhibitor GW4869 suppressed the QDs enriched in the brains of mice with a 4T1-Luc breast cancer xenograft. Interestingly, Exo heterogeneity affects the distal trafficking of enveloped QDs. Exo derived from tumorous HeLa cells, not macrophages, that were enriched in functional proteins with cell adhesion, cell migration, axon guidance, and cell motility, showed a better capacity for the remote trafficking of QDs. This study proposes Exo as a vehicle to deliver exogenous NPs to translocate across the distal barrier and provides further information for biomedical application and the risk assessment of NPs.

Comprehensive Proteomic Analysis of the Differential Expression of 83 Proteins Following Intracortical Microelectrode Implantation

Intracortical microelectrodes (IMEs) are devices designed to be implanted into the cerebral cortex for various neuroscience and neuro-engineering applications. A critical feature of these devices is their ability to detect neural activity from individual neurons. Currently, IMEs are limited by chronic failure, largely considered to be caused by the prolonged neuroinflammatory response to the implanted devices. Over the decades, characterization of the neuroinflammatory response has grown in sophistication, with the most recent advances including advanced genomics and spatially resolved transcriptomics. While gene expression studies increase our broad understanding of the relationship between IMEs and cortical tissue, advanced proteomic techniques have not been reported. Proteomic evaluation is necessary to describe the diverse changes in protein expression specific to neuroinflammation, neurodegeneration, or tissue and cellular viability, which could lead to the development of more targeted intervention strategies designed to improve IME function. In this study, we have characterized the expression of 83 proteins within 180 μm of the IME implant site at 4-, 8-, and 16-weeks post-implantation. We identified potential targets for immunotherapies, as well as key pathways and functions that contribute to neuronal dieback around the IME implant.

Bacteria Invade the Brain Following Sterile Intracortical Microelectrode Implantation

Brain-machine interface performance is largely affected by the neuroinflammatory responses resulting in large part from blood-brain barrier (BBB) damage following intracortical microelectrode implantation. Recent findings strongly suggest that certain gut bacterial constituents penetrate the BBB and are resident in various brain regions of rodents and humans, both in health and disease. Therefore, we hypothesized that damage to the BBB caused by microelectrode implantation could amplify dysregulation of the microbiome-gut-brain axis. Here, we report that bacteria, including those commonly found in the gut, enter the brain following intracortical microelectrode implantation in mice implanted with single-shank silicon microelectrodes. Systemic antibiotic treatment of mice implanted with microelectrodes to suppress bacteria resulted in differential expression of bacteria in the brain tissue and a reduced acute inflammatory response compared to untreated controls, correlating with temporary improvements in microelectrode recording performance. Long-term antibiotic treatment resulted in worsening microelectrode recording performance and dysregulation of neurodegenerative pathways. Fecal microbiome composition was similar between implanted mice and an implanted human, suggesting translational findings. However, a significant portion of invading bacteria was not resident in the brain or gut. Together, the current study established a paradigm-shifting mechanism that may contribute to chronic intracortical microelectrode recording performance and affect overall brain health following intracortical microelectrode implantation.

The effect of a Mn(III)tetrakis(4-benzoic acid)porphyrin (MnTBAP) coating on the chronic recording performance of planar silicon intracortical microelectrode arrays

Intracortical microelectrode arrays (MEAs) are used to record neural activity. However, their implantation initiates a neuroinflammatory cascade, involving the accumulation of reactive oxygen species, leading to interface failure. Here, we coated commercially-available MEAs with Mn(III)tetrakis(4-benzoic acid)porphyrin (MnTBAP), to mitigate oxidative stress. First, we assessed the in vitro cytotoxicity of modified sample substrates. Then, we implanted 36 rats with uncoated, MnTBAP-coated ("Coated"), or (3-Aminopropyl)triethoxysilane (APTES)-coated devices - an intermediate step in the coating process. We assessed electrode performance during the acute (1-5 weeks), sub-chronic (6-11 weeks), and chronic (12-16 weeks) phases after implantation. Three subsets of animals were euthanized at different time points to assess the acute, sub-chronic and chronic immunohistological responses. Results showed that MnTBAP coatings were not cytotoxic in vitro, and their implantation in vivo improved the proportion of electrodes during the sub-chronic and chronic phases; APTES coatings resulted in failure of the neural interface during the chronic phase. In addition, MnTBAP coatings improved the quality of the signal throughout the study and reduced the neuroinflammatory response around the implant as early as two weeks, an effect that remained consistent for months post-implantation. Together, these results suggest that MnTBAP coatings are a potentially useful modification to improve MEA reliability.

Cell-specific alterations in autophagy-lysosomal activity near the chronically implanted microelectrodes

Intracortical microelectrodes that can record and stimulate brain activity have become a valuable technique for basic science research and clinical applications. However, long-term implantation of these microelectrodes can lead to progressive neurodegeneration in the surrounding microenvironment, characterized by elevation in disease-associated markers. Dysregulation of autophagy-lysosomal degradation, a major intracellular waste removal process, is considered a key factor in the onset and progression of neurodegenerative diseases. It is plausible that similar dysfunctions in autophagy-lysosomal degradation contribute to tissue degeneration following implantation-induced focal brain injury, ultimately impacting recording performance. To understand how the focal, persistent brain injury caused by long-term microelectrode implantation impairs autophagy-lysosomal pathway, we employed two-photon microscopy and immunohistology. This investigation focused on the spatiotemporal characterization of autophagy-lysosomal activity near the chronically implanted microelectrode. We observed an aberrant accumulation of immature autophagy vesicles near the microelectrode over the chronic implantation period. Additionally, we found deficits in autophagy-lysosomal clearance proximal to the chronic implant, which was associated with an accumulation of autophagy cargo and a reduction in lysosomal protease level during the chronic period. Furthermore, our evidence demonstrates reactive astrocytes have myelin-containing lysosomes near the microelectrode, suggesting its role of myelin engulfment during acute implantation period. Together, this study sheds light on the process of brain tissue degeneration caused by long-term microelectrode implantation, with a specific focus on impaired intracellular waste degradation.

Advancing the interfacing performances of chronically implantable neural probes in the era of CMOS neuroelectronics

Tissue penetrating microelectrode neural probes can record electrophysiological brain signals at resolutions down to single neurons, making them invaluable tools for neuroscience research and Brain-Computer-Interfaces (BCIs). The known gradual decrease of their electrical interfacing performances in chronic settings, however, remains a major challenge. A key factor leading to such decay is Foreign Body Reaction (FBR), which is the cascade of biological responses that occurs in the brain in the presence of a tissue damaging artificial device. Interestingly, the recent adoption of Complementary Metal Oxide Semiconductor (CMOS) technology to realize implantable neural probes capable of monitoring hundreds to thousands of neurons simultaneously, may open new opportunities to face the FBR challenge. Indeed, this shift from passive Micro Electro-Mechanical Systems (MEMS) to active CMOS neural probe technologies creates important, yet unexplored, opportunities to tune probe features such as the mechanical properties of the probe, its layout, size, and surface physicochemical properties, to minimize tissue damage and consequently FBR. Here, we will first review relevant literature on FBR to provide a better understanding of the processes and sources underlying this tissue response. Methods to assess FBR will be described, including conventional approaches based on the imaging of biomarkers, and more recent transcriptomics technologies. Then, we will consider emerging opportunities offered by the features of CMOS probes. Finally, we will describe a prototypical neural probe that may meet the needs for advancing clinical BCIs, and we propose axial insertion force as a potential metric to assess the influence of probe features on acute tissue damage and to control the implantation procedure to minimize iatrogenic injury and subsequent FBR.

Antioxidant Dimethyl Fumarate Temporarily but Not Chronically Improves Intracortical Microelectrode Performance

Intracortical microelectrode arrays (MEAs) can be used in a range of applications, from basic neuroscience research to providing an intimate interface with the brain as part of a brain-computer interface (BCI) system aimed at restoring function for people living with neurological disorders or injuries. Unfortunately, MEAs tend to fail prematurely, leading to a loss in functionality for many applications. An important contributing factor in MEA failure is oxidative stress resulting from chronically inflammatory-activated microglia and macrophages releasing reactive oxygen species (ROS) around the implant site. Antioxidants offer a means for mitigating oxidative stress and improving tissue health and MEA performance. Here, we investigate using the clinically available antioxidant dimethyl fumarate (DMF) to reduce the neuroinflammatory response and improve MEA performance in a rat MEA model. Daily treatment of DMF for 16 weeks resulted in a significant improvement in the recording capabilities of MEA devices during the sub-chronic (Weeks 5-11) phase (42% active electrode yield vs. 35% for control). However, these sub-chronic improvements were lost in the chronic implantation phase, as a more exacerbated neuroinflammatory response occurs in DMF-treated animals by 16 weeks post-implantation. Yet, neuroinflammation was indiscriminate between treatment and control groups during the sub-chronic phase. Although worse for chronic use, a temporary improvement (<12 weeks) in MEA performance is meaningful. Providing short-term improvement to MEA devices using DMF can allow for improved use for limited-duration studies. Further efforts should be taken to explore the mechanism behind a worsened neuroinflammatory response at the 16-week time point for DMF-treated animals and assess its usefulness for specific applications.

Pro-myelinating clemastine administration improves recording performance of chronically implanted microelectrodes and nearby neuronal health

Intracortical microelectrodes have become a useful tool in neuroprosthetic applications in the clinic and to understand neurological disorders in basic neurosciences. Many of these brain-machine interface technology applications require successful long-term implantation with high stability and sensitivity. However, the intrinsic tissue reaction caused by implantation remains a major failure mechanism causing loss of recorded signal quality over time. Oligodendrocytes remain an underappreciated intervention target to improve chronic recording performance. These cells can accelerate action potential propagation and provides direct metabolic support for neuronal health and functionality. However, implantation injury causes oligodendrocyte degeneration and leads to progressive demyelination in surrounding brain tissue. Previous work highlighted that healthy oligodendrocytes are necessary for greater electrophysiological recording performance and the prevention of neuronal silencing around implanted microelectrodes over the chronic implantation period. Thus, we hypothesize that enhancing oligodendrocyte activity with a pharmaceutical drug, Clemastine, will prevent the chronic decline of microelectrode recording performance. Electrophysiological evaluation showed that the promyelination Clemastine treatment significantly elevated the signal detectability and quality, rescued the loss of multi-unit activity, and increased functional interlaminar connectivity over 16-weeks of implantation. Additionally, post-mortem immunohistochemistry showed that increased oligodendrocyte density and myelination coincided with increased survival of both excitatory and inhibitory neurons near the implant. Overall, we showed a positive relationship between enhanced oligodendrocyte activity and neuronal health and functionality near the chronically implanted microelectrode. This study shows that therapeutic strategy that enhance oligodendrocyte activity is effective for integrating the functional device interface with brain tissue over chronic implantation period.

Platelets and hemostatic proteins are co-localized with chronic neuroinflammation surrounding implanted intracortical microelectrodes

Intracortical microelectrodes induce vascular injury upon insertion into the cortex. As blood vessels rupture, blood proteins and blood-derived cells (including platelets) are introduced into the 'immune privileged' brain tissues at higher-than-normal levels, passing through the damaged blood-brain barrier. Blood proteins adhere to implant surfaces, increasing the likelihood of cellular recognition leading to activation of immune and inflammatory cells. Persistent neuroinflammation is a major contributing factor to declining microelectrode recording performance. We investigated the spatial and temporal relationship of blood proteins fibrinogen and von Willebrand Factor (vWF), platelets, and type IV collagen, in relation to glial scarring markers for microglia and astrocytes following implantation of non-functional multi-shank silicon microelectrode probes into rats. Together with type IV collagen, fibrinogen and vWF augment platelet recruitment, activation, and aggregation. Our main results indicate blood proteins participating in hemostasis (fibrinogen and vWF) persisted at the microelectrode interface for up to 8-weeks after implantation. Further, type IV collagen and platelets surrounded the probe interface with similar spatial and temporal trends as vWF and fibrinogen. In addition to prolonged blood-brain barrier instability, specific blood and extracellular matrix proteins may play a role in promoting the inflammatory activation of platelets and recruitment to the microelectrode interface. STATEMENT OF SIGNIFICANCE: Implanted microelectrodes have substantial potential for restoring function to people with paralysis and amputation by providing signals that feed into natural control algorithms that drive prosthetic devices. Unfortunately, these microelectrodes do not display robust performance over time. Persistent neuroinflammation is widely thought to be a primary contributor to the devices' progressive decline in performance. Our manuscript reports on the highly local and persistent accumulation of platelets and hemostatic blood proteins around the microelectrode interface of brain implants. To our knowledge neuroinflammation driven by cellular and non-cellular responses associated with hemostasis and coagulation has not been rigorously quantified elsewhere. Our findings identify potential targets for therapeutic intervention and a better understanding of the driving mechanisms to neuroinflammation in the brain.

Chemically revised conducting polymers with inflammation resistance for intimate bioelectronic electrocoupling

Conducting polymers offer attractive mixed ionic-electronic conductivity, tunable interfacial barrier with metal, tissue matchable softness, and versatile chemical functionalization, making them robust to bridge the gap between brain tissue and electronic circuits. This review focuses on chemically revised conducting polymers, combined with their superior and controllable electrochemical performance, to fabricate long-term bioelectronic implants, addressing chronic immune responses, weak neuron attraction, and long-term electrocommunication instability challenges. Moreover, the promising progress of zwitterionic conducting polymers in bioelectronic implants (≥4 weeks stable implantation) is highlighted, followed by a comment on their current evolution toward selective neural coupling and reimplantable function. Finally, a critical forward look at the future of zwitterionic conducting polymers for in vivo bioelectronic devices is provided.

Activation of inflammasomes and their effects on neuroinflammation at the microelectrode-tissue interface in intracortical implants

Invasive neuroprosthetics rely on microelectrodes (MEs) to record or stimulate the activity of large neuron assemblies. However, MEs are subjected to tissue reactivity in the central nervous system (CNS) due to the foreign body response (FBR) that contribute to chronic neuroinflammation and ultimately result in ME failure. An endogenous, acute set of mechanisms responsible for the recognition and targeting of foreign objects, called the innate immune response, immediately follows the ME implant-induced trauma. Inflammasomes are multiprotein structures that play a critical role in the initiation of an innate immune response following CNS injuries. The activation of inflammasomes facilitates a range of innate immune response cascades and results in neuroinflammation and programmed cell death. Despite our current understanding of inflammasomes, their roles in the context of neural device implantation remain unknown. In this study, we implanted a non-functional Utah electrode array (UEA) into the rat somatosensory cortex and studied the inflammasome signaling and the corresponding downstream effects on inflammatory cytokine expression and the inflammasome-mediated cell death mechanism of pyroptosis. Our results not only demonstrate the continuous activation of inflammasomes and their contribution to neuroinflammation at the electrode-tissue interface but also reveal the therapeutic potential of targeting inflammasomes to attenuate the FBR in invasive neuroprosthetics.

Spatiotemporal Expression of RNA-Seq Identified Proteins at the Electrode Interface

Implantation of electrodes in the brain can be used to record from or stimulate neural tissues to treat neurological disease and injury. However, the tissue response to implanted devices can limit their functional longevity. Recent RNA-seq datasets identify hundreds of genes associated with gliosis, neuronal function, myelination, and cellular metabolism that are spatiotemporally expressed in neural tissues following the insertion of microelectrodes. To validate mRNA as a predictor of protein expression, this study evaluates a sub-set of RNA-seq identified proteins (RSIP) at 24-hours, 1-week, and 6-weeks post-implantation using quantitative immunofluorescence methods. This study found that expression of RSIPs associated with glial activation (Glial fibrillary acidic protein (GFAP), Polypyrmidine tract binding protein-1 (Ptbp1)), neuronal structure (Neurofilament heavy chain (Nefh), Proteolipid protein-1 (Plp1), Myelin Basic Protein (MBP)), and iron metabolism (Transferrin (TF), Ferritin heavy chain-1 (Fth1)) reinforce transcriptional data. This study also provides additional context to the cellular distribution of RSIPs using a MATLAB-based approach to quantify immunofluorescence intensity within specific cell types. Ptbp1, TF, and Fth1 were found to be spatiotemporally distributed within neurons, astrocytes, microglia, and oligodendrocytes at the device interface relative to distal and contralateral tissues. The altered distribution of RSIPs relative to distal tissue is largely localized within 100µm of the device injury, which approaches the functional recording range of implanted electrodes. This study provides evidence that RNA-sequencing can be used to predict protein-level changes in cortical tissues and that RSIPs can be further investigated to identify new biomarkers of the tissue response that influence signal quality. STATEMENT OF SIGNIFICANCE: : Microelectrode arrays implanted into the brain are useful tools that can be used to study neuroscience and to treat pathological conditions in a clinical setting. The tissue response to these devices, however, can severely limit their functional longevity. Transcriptomics has deepened the understandings of the tissue response by revealing numerous genes which are differentially expressed following device insertion. This manuscript provides validation for the use of transcriptomics to characterize the tissue response by evaluating a subset of known differentially expressed genes at the protein level around implanted electrodes over time. In additional to validating mRNA-to-protein relationships at the device interface, this study has identified emerging trends in the spatiotemporal distribution of proteins involved with glial activation, neuronal remodeling, and essential iron binding proteins around implanted silicon devices. This study additionally provides a new MATLAB based methodology to quantify protein distribution within discrete cell types at the device interface which may be used as biomarkers for further study or therapeutic intervention in the future.

Pro-myelinating Clemastine administration improves recording performance of chronically implanted microelectrodes and nearby neuronal health

Intracortical microelectrodes have become a useful tool in neuroprosthetic applications in the clinic and to understand neurological disorders in basic neurosciences. Many of these brain-machine interface technology applications require successful long-term implantation with high stability and sensitivity. However, the intrinsic tissue reaction caused by implantation remains a major failure mechanism causing loss of recorded signal quality over time. Oligodendrocytes remain an underappreciated intervention target to improve chronic recording performance. These cells can accelerate action potential propagation and provides direct metabolic support for neuronal health and functionality. However, implantation injury causes oligodendrocyte degeneration and leads to progressive demyelination in surrounding brain tissue. Previous work highlighted that healthy oligodendrocytes are necessary for greater electrophysiological recording performance and the prevention of neuronal silencing around implanted microelectrodes over chronic implantation. Thus, we hypothesize that enhancing oligodendrocyte activity with a pharmaceutical drug, Clemastine, will prevent the chronic decline of microelectrode recording performance. Electrophysiological evaluation showed that the promyelination Clemastine treatment significantly elevated the signal detectability and quality, rescued the loss of multi-unit activity, and increased functional interlaminar connectivity over 16-weeks of implantation. Additionally, post-mortem immunohistochemistry showed that increased oligodendrocyte density and myelination coincided with increased survival of both excitatory and inhibitory neurons near the implant. Overall, we showed a positive relationship between enhanced oligodendrocyte activity and neuronal health and functionality near the chronically implanted microelectrode. This study shows that therapeutic strategy that enhance oligodendrocyte activity is effective for integrating the functional device interface with brain tissue over chronic implantation period.

Abstract Figure

Laminin Adsorption and Adhesion of Neurons and Glial Cells on Carbon Implanted Titania Nanotube Scaffolds for Neural Implant Applications

Interfacing neurons persistently to conductive matter constitutes one of the key challenges when designing brain-machine interfaces such as neuroelectrodes or retinal implants. Novel materials approaches that prevent occurrence of loss of long-term adhesion, rejection reactions, and glial scarring are highly desirable. Ion doped titania nanotube scaffolds are a promising material to fulfill all these requirements while revealing sufficient electrical conductivity, and are scrutinized in the present study regarding their neuron-material interface. Adsorption of laminin, an essential extracellular matrix protein of the brain, is comprehensively analyzed. The implantation-dependent decline in laminin adsorption is revealed by employing surface characteristics such as nanotube diameter, ζ-potential, and surface free energy. Moreover, the viability of U87-MG glial cells and SH-SY5Y neurons after one and four days are investigated, as well as the material's cytotoxicity. The higher conductivity related to carbon implantation does not affect the viability of neurons, although it impedes glial cell proliferation. This gives rise to novel titania nanotube based implant materials with long-term stability, and could reduce undesirable glial scarring.

Effects of central nervous system electrical stimulation on non-neuronal cells

Over the past few decades, much progress has been made in the clinical use of electrical stimulation of the central nervous system (CNS) to treat an ever-growing number of conditions from Parkinson's disease (PD) to epilepsy as well as for sensory restoration and many other applications. However, little is known about the effects of microstimulation at the cellular level. Most of the existing research focuses on the effects of electrical stimulation on neurons. Other cells of the CNS such as microglia, astrocytes, oligodendrocytes, and vascular endothelial cells have been understudied in terms of their response to stimulation. The varied and critical functions of these cell types are now beginning to be better understood, and their vital roles in brain function in both health and disease are becoming better appreciated. To shed light on the importance of the way electrical stimulation as distinct from device implantation impacts non-neuronal cell types, this review will first summarize common stimulation modalities from the perspective of device design and stimulation parameters and how these different parameters have an impact on the physiological response. Following this, what is known about the responses of different cell types to different stimulation modalities will be summarized, drawing on findings from both clinical studies as well as clinically relevant animal models and in vitro systems.

Cleanroom strategies for micro- and nano-fabricating flexible implantable neural electronics

Implantable electronic neural interfaces typically take the form of probes and are made with rigid materials such as silicon and metals. These have advantages such as compatibility with integrated microchips, simple implantation and high-density nanofabrication but tend to be lacking in terms of biointegration, biocompatibility and durability due to their mechanical rigidity. This leads to damage to the device or, more importantly, the brain tissue surrounding the implant. Flexible polymer-based probes offer superior biocompatibility in terms of surface biochemistry and better matched mechanical properties. Research which aims to bring the fabrication of electronics on flexible polymer substrates to the nano-regime is remarkably sparse, despite the push for flexible consumer electronics in the last decade or so. Cleanroom-based nanofabrication techniques such as photolithography have been used as pattern transfer methods by the semiconductor industry to produce single nanometre scale devices and are now also used for making flexible circuit boards. There is still much scope for miniaturizing flexible electronics further using photolithography, bringing the possibility of nanoscale, non-invasive, high-density flexible neural interfacing. This work explores the fabrication challenges of using photolithography and complementary techniques in a cleanroom for producing flexible electronic neural probes with nanometre-scale features. This article is part of the theme issue 'Advanced neurotechnologies: translating innovation for health and well-being'.

S1PR3, as a Core Protein Related to Ischemic Stroke, is Involved in the Regulation of Blood–Brain Barrier Damage

Background: Ischemic stroke is the most common stroke incident. Sphingosine-1-phosphate (S1P) receptor 3 (S1PR3) is a member of the downstream G protein-coupled receptor family of S1P. The effect of S1PR3 on ischemic stroke remains elusive.

Methods: We downloaded two middle cerebral artery occlusion (MCAO) microarray datasets from the Gene Expression Omnibus (GEO) database and screened differentially expressed genes (DEGs). Then, we performed a weighted gene coexpression network analysis (WGCNA) and identified the core module genes related to ischemic stroke. We constructed a protein–protein interaction (PPI) network for the core genes in which DEGs and WGCNA intersected. Finally, we discovered that S1PR3 was involved as the main member of the red proteome. Then, we explored the mechanism of S1PR3 in the mouse tMCAO model. The S1PR3-specific inhibitor CAY10444 was injected into the abdominal cavity of mice after cerebral ischemia/reperfusion (I/R) injury, and changes in the expression of blood–brain barrier-related molecules were measured using PCR, western blotting, and immunofluorescence staining.

Results: Both GEO datasets showed that S1PR3 was upregulated during cerebral I/R in mice. WGCNA revealed that the light yellow module had the strongest correlation with the occurrence of IS. We determined the overlap with DEGs, identified 146 core genes that are potentially related to IS, and constructed a PPI network. Finally, S1PR3 was found to be the main member of the red proteome. In the mouse cerebral I/R model, S1PR3 expression increased 24 h after ischemia. After the administration of CAY10444, brain edema and neurological deficits in mice were ameliorated. CAY10444 rescued the decreased expression of the tight junction (TJ) proteins zonula occludens 1 (ZO1) and occludin after ischemia induced by transient MCAO (tMCAO) and reduced the increase in aquaporin 4 (AQP4) levels after tMCAO, preserving the integrity of the BBB. Finally, we found that S1PR3 is involved in regulating the mitogen-activated protein kinase (MAPK) and (phosphatidylinositol-3 kinase/serine-threonine kinase) PI3K-Akt signaling pathways.

Conclusion: S1PR3 participates in the regulation of blood–brain barrier damage after cerebral I/R. S1PR3 is expected to be an indicator and predictor of cerebral ischemia, and drugs targeting S1PR3 may also provide new ideas for clinical medications.

Investigation of the Feasibility of Ventricular Delivery of Resveratrol to the Microelectrode Tissue Interface

(1) Background: Intracortical microelectrodes (IMEs) are essential to basic brain research and clinical brain-machine interfacing applications. However, the foreign body response to IMEs results in chronic inflammation and an increase in levels of reactive oxygen and nitrogen species (ROS/RNS). The current study builds on our previous work, by testing a new delivery method of a promising antioxidant as a means of extending intracortical microelectrodes performance. While resveratrol has shown efficacy in improving tissue response, chronic delivery has proven difficult because of its low solubility in water and low bioavailability due to extensive first pass metabolism. (2) Methods: Investigation of an intraventricular delivery of resveratrol in rats was performed herein to circumvent bioavailability hurdles of resveratrol delivery to the brain. (3) Results: Intraventricular delivery of resveratrol in rats delivered resveratrol to the electrode interface. However, intraventricular delivery did not have a significant impact on electrophysiological recordings over the six-week study. Histological findings indicated that rats receiving intraventricular delivery of resveratrol had a decrease of oxidative stress, yet other biomarkers of inflammation were found to be not significantly different from control groups. However, investigation of the bioavailability of resveratrol indicated a decrease in resveratrol accumulation in the brain with time coupled with inconsistent drug elution from the cannulas. Further inspection showed that there may be tissue or cellular debris clogging the cannulas, resulting in variable elution, which may have impacted the results of the study. (4) Conclusions: These results indicate that the intraventricular delivery approach described herein needs further optimization, or may not be well suited for this application.

Development and Characterization of Novel Conductive Sensing Fibers for In Vivo Nerve Stimulation

Advancements in electrode technologies to both stimulate and record the central nervous system's electrical activities are enabling significant improvements in both the understanding and treatment of different neurological diseases. However, the current neural recording and stimulating electrodes are metallic, requiring invasive and damaging methods to interface with neural tissue. These electrodes may also degrade, resulting in additional invasive procedures. Furthermore, metal electrodes may cause nerve damage due to their inherent rigidity. This paper demonstrates that novel electrically conductive organic fibers (ECFs) can be used for direct nerve stimulation. The ECFs were prepared using a standard polyester material as the structural base, with a carbon nanotube ink applied to the surface as the electrical conductor. We report on three experiments: the first one to characterize the conductive properties of the ECFs; the second one to investigate the fiber cytotoxic properties in vitro; and the third one to demonstrate the utility of the ECF for direct nerve stimulation in an in vivo rodent model.

Long-term in vivo two-photon imaging of the neuroinflammatory response to intracortical implants and micro-vessel disruptions in awake mice

Our understanding of biomaterials in the brain have been greatly enhanced by advancements in in vivo imaging technologies such as two-photon microscopy. However, when applied to chronic studies, two-photon microscopy enables high-resolution imaging only in superficial regions due to inflammatory responses introduced by the craniotomy and insertion of foreign biomaterials. Microprisms provide a unique vertical view from brain surface to ~1 mm deep or more (depending on the size of the microprisms) which may break through this limitation on imaging depth. Although microprism has been used in the field of neuroscience, the in vivo foreign body responses to the microprism implant have yet to be fully elucidated. This is of important concern in broader applications of this approach, especially for neuroinflammation-sensitive studies. In this work, we first assessed the activation of microglia/macrophages for 16 weeks after microprism implantation using two-photon microscopy in awake CX3CR1-GFP mice. The imaging window became clear from bleedings after ~2 weeks and the maximum imaging distance (in the horizontal direction) stabilized at around 500 μm after ~5 weeks. We also quantified the microglial morphology from week 3 to week 16 post-implantation. Compared to non-implant controls, microglia near the microprism showed higher cell density, smaller soma, and shorter and less branched processes in the early-chronic phase. After week 5, microglial morphology further than 100 μm from the microprism was generally similar to microglia in the control group. In addition, time-lapse imaging confirmed that microglial processes were surveying normally from week 3, even for microglia as close as 50 μm away. These morphological analyses and dynamic imaging results suggest that microglia around chronically implanted microprism eventually exhibit inactive phenotypes. Next, we examined microglial/macrophage responses following laser induced micro-vessel disruptions as an example application of microprism implantation for neuroinflammation related studies. Through the microprism, we captured microglial/macrophage polarization and migration, as well as blood flow changes after the insult for additional 16 weeks. To our surprise, microglia/macrophage aggregation around the insult site was sustained over the 16-week observation period. This work demonstrates the feasibility of using microprisms for long-term characterizations of inflammatory responses to other injuries including implantable devices at deeper depths than that achievable by conventional two-photon microscopy.

Intracortical Microelectrode Array Unit Yield under Chronic Conditions: A Comparative Evaluation

While microelectrode arrays (MEAs) offer the promise of elucidating functional neural circuitry and serve as the basis for a cortical neuroprosthesis, the challenge of designing and demonstrating chronically reliable technology remains. Numerous studies report “chronic” data but the actual time spans and performance measures corresponding to the experimental work vary. In this study, we reviewed the experimental durations that constitute chronic studies across a range of MEA types and animal species to gain an understanding of the widespread variability in reported study duration. For rodents, which are the most commonly used animal model in chronic studies, we examined active electrode yield (AEY) for different array types as a means to contextualize the study duration variance, as well as investigate and interpret the performance of custom devices in comparison to conventional MEAs. We observed wide-spread variance within species for the chronic implantation period and an AEY that decayed linearly in rodent models that implanted commercially-available devices. These observations provide a benchmark for comparing the performance of new technologies and highlight the need for consistency in chronic MEA studies. Additionally, to fully derive performance under chronic conditions, the duration of abiotic failure modes, biological processes induced by indwelling probes, and intended application of the device are key determinants.

Increase of blood-brain barrier leakage is related to cognitive decline in vascular mild cognitive impairment

BACKGROUND

Blood-brain barrier (BBB) breakdown, as an early biomarker for vascular mild cognitive impairment (vMCI), has only been validated by a few studies. The aim of this study was to investigate whether compromised BBB integrity is involved in vMCI patients, and detect the relationship between BBB breakdown and cognitive function. BBB leakage in vMCI was explored, and the relationship between BBB leakage and cognitive function was discussed in this study.

METHODS

This is a cross-sectional study involving 26 vMCI patients and 21 sex- and age-matched healthy controls. Dynamic contrast-enhanced-magnetic resonance imaging was performed for all participants, to determine BBB leakage. Leakage volume, leakage rate, and fractional blood plasma volume (Vp) in the grey and white matter were evaluated. Neuropsychological tests were used to determine cognitive function. Leakage rate, leakage volume, and Vp in different brain locations, including deep grey matter, cortical grey matter, white matter hyperintensity, and normal-appearing white matter were compared between the two groups.

RESULTS

Multivariable linear regression analyses revealed that in all regions of interest, the leakage rate was significantly higher in vMCI patients relative to controls. Leakage volume in normal-appearing white matter and white matter hyperintensity were significantly higher, while Vp in normal-appearing white matter, deep grey matter, and cortical grey matter were significantly lower in vMCI patients. Moreover, Montreal Cognitive Assessment scores decreased with the increase of leakage rate in white matter hyperintensity.

CONCLUSION

Increased BBB permeability was detected in vMCI patients and was related to cognitive decline, which suggested that BBB breakdown might be involved in cognitive dysfunction pathogenesis.

Advances in Carbon-Based Microfiber Electrodes for Neural Interfacing

Neural interfacing devices using penetrating microelectrode arrays have emerged as an important tool in both neuroscience research and medical applications. These implantable microelectrode arrays enable communication between man-made devices and the nervous system by detecting and/or evoking neuronal activities. Recent years have seen rapid development of electrodes fabricated using flexible, ultrathin carbon-based microfibers. Compared to electrodes fabricated using rigid materials and larger cross-sections, these microfiber electrodes have been shown to reduce foreign body responses after implantation, with improved signal-to-noise ratio for neural recording and enhanced resolution for neural stimulation. Here, we review recent progress of carbon-based microfiber electrodes in terms of material composition and fabrication technology. The remaining challenges and future directions for development of these arrays will also be discussed. Overall, these microfiber electrodes are expected to improve the longevity and reliability of neural interfacing devices.

Tembusu Virus entering the central nervous system caused nonsuppurative encephalitis without disrupting the blood-brain barrier

Tembusu Virus (TMUV) is an emerging and re-emerging zoonotic pathogen that adversely affects poultry industry in recent years. TMUV disease is characterized by nonsuppurative encephalitis in ducklings. The duckling infection model was established to study the mechanism of TMUV crossing the blood-brain barrier (BBB) into the central nervous system (CNS). Here, we showed that no obvious clinical symptoms and enhancement of BBB permeability occurred at the early stage of infection (3∼5 dpi). While simultaneously virus particles were observed by transmission electron microscopy in the brain, inducing the accumulation of inflammatory cytokines. Neurological symptoms and disruption of BBB appeared at the intermediate stage of infection (7∼9 dpi). It was confirmed that TMUV could survive and propagate in brain microvascular endothelial cells (BMECs), but did not affect the permeability of BBB in vivo and in vitro at an early date. In conclusion, TMUV enters the CNS then causes encephalitis, and finally destruct the BBB, which may be due to the direct effect of TMUV on BMECs and the subsequent response of "inflammatory storm".IMPORTANCE The TMUV disease has caused huge losses to the poultry industry in Asia, which is potentially harmful to public health. Neurological symptoms and their sequelae are the main characters of this disease. However, the mechanism of how this virus enters the brain and causes encephalitis is unclear. In this study, we confirmed that the virus entered the CNS and then massively destroyed BBB and the BBB damage was closely associated with the subsequent outbreak of inflammation. TMUV may enter the CNS through the transcellular and "Trojan horse" pathways. These findings can fill the knowledge gap in the pathogenesis of TMUV-infected poultry and be benefit for the treatment of TMUV disease. What's more, TMUV is a representative to study the infection of avian flavivirus. Therefore, our studies have significances both for understanding of the full scope of mechanisms of TMUV and other flavivirus infection, and conceivably, for therapeutics.

The complement cascade at the Utah microelectrode-tissue interface

Devices implanted within the central nervous system (CNS) are subjected to tissue reactivity due to the lack of biocompatibility between implanted material and the cells' microenvironment. Studies have attributed blood-brain barrier disruption, inflammation, and oxidative stress as main contributing factors that lead to electrode recording failure. The complement cascade is a part of the innate immunity that focuses on recognizing and targeting foreign objects; however, its role in the context of neural implants is substantially unknown. In this study, we implanted a non-functional 4x4 Utah microelectrode array (UEA) into the somatosensory cortex and studied the complement cascade via combined gene and immunohistochemistry quantification at acute (48-h), sub-acute (1-week), and early chronic (4-weeks) time points. The results of this study demonstrate the activation and continuation of the complement cascade at the electrode-tissue interface, illustrating the therapeutic potential of modulating the foreign body response via the complement cascade.

In Vivo Neuroelectrophysiological Monitoring of Atomically Precise Au25 Clusters at an Ultrahigh Injected Dose

Atomically precise Au₂₅(SG)₁₈ clusters have shown great promise in near-infrared II cerebrovascular imaging, X-ray imaging, and cancer radiotherapy due to their high atomic number, unique molecular-like electronic structure, and renal clearable properties. Therefore, it is important to study the in vivo toxicity of Au₂₅ clusters. Unfortunately, previous toxicological investigations focused on low injected doses (<100 mg kg^-1) and routine research methods, such as blood chemistry and biochemistry, which cannot reflect neurotoxicity or tiny changes in neural activity. In this work, in vivo neuroelectrophysiology of Au₂₅ clusters at ultrahigh injected doses (200, 300, and 500 mg kg^-1) was investigated. Local field potential showed that the Au₂₅-treated mice showed a spike in delta rhythm and moved to lower frequency over time. The power spectrum showed a 38.3% reduction in the peak value at 10 h post-injection of Au₂₅ clusters compared with 3 h post-injection, which gradually became close to the normal level, indicating no permanent damage to the nervous system. Moreover, no significant structural changes were found in both neurons and glial cells at the histological level. These results of in vivo neuroelectrophysiology will encourage scientists to make more exciting discoveries on nervous system diseases by employing Au₂₅ clusters even at ultrahigh injected doses.

Investigating the Association between Motor Function, Neuroinflammation, and Recording Metrics in the Performance of Intracortical Microelectrode Implanted in Motor Cortex

Long-term reliability of intracortical microelectrodes remains a challenge for increased acceptance and deployment. There are conflicting reports comparing measurements associated with recording quality with postmortem histology, in attempts to better understand failure of intracortical microelectrodes (IMEs). Our group has recently introduced the assessment of motor behavior tasks as another metric to evaluate the effects of IME implantation. We hypothesized that adding the third dimension to our analysis, functional behavior testing, could provide substantial insight on the health of the tissue, success of surgery/implantation, and the long-term performance of the implanted device. Here we present our novel analysis scheme including: (1) the use of numerical formal concept analysis (nFCA) and (2) a regression analysis utilizing modern model/variable selection. The analyses found complimentary relationships between the variables. The histological variables for glial cell activation had associations between each other, as well as the neuronal density around the electrode interface. The neuronal density had associations to the electrophysiological recordings and some of the motor behavior metrics analyzed. The novel analyses presented herein describe a valuable tool that can be utilized to assess and understand relationships between diverse variables being investigated. These models can be applied to a wide range of ongoing investigations utilizing various devices and therapeutics.

Toward Standardization of Electrophysiology and Computational Tissue Strain in Rodent Intracortical Microelectrode Models

Progress has been made in the field of neural interfacing using both mouse and rat models, yet standardization of these models' interchangeability has yet to be established. The mouse model allows for transgenic, optogenetic, and advanced imaging modalities which can be used to examine the biological impact and failure mechanisms associated with the neural implant itself. The ability to directly compare electrophysiological data between mouse and rat models is crucial for the development and assessment of neural interfaces. The most obvious difference in the two rodent models is size, which raises concern for the role of device-induced tissue strain. Strain exerted on brain tissue by implanted microelectrode arrays is hypothesized to affect long-term recording performance. Therefore, understanding any potential differences in tissue strain caused by differences in the implant to tissue size ratio is crucial for validating the interchangeability of rat and mouse models. Hence, this study is aimed at investigating the electrophysiological variances and predictive device-induced tissue strain. Rat and mouse electrophysiological recordings were collected from implanted animals for eight weeks. A finite element model was utilized to assess the tissue strain from implanted intracortical microelectrodes, taking into account the differences in the depth within the cortex, implantation depth, and electrode geometry between the two models. The rat model demonstrated a larger percentage of channels recording single unit activity and number of units recorded per channel at acute but not chronic time points, relative to the mouse model Additionally, the finite element models also revealed no predictive differences in tissue strain between the two rodent models. Collectively our results show that these two models are comparable after taking into consideration some recommendations to maintain uniform conditions for future studies where direct comparisons of electrophysiological and tissue strain data between the two animal models will be required.

Therapeutic hypothermia reduces cortical inflammation associated with utah array implants

OBJECTIVE

Neuroprosthetics hold tremendous promise to restore function through brain-computer interfaced devices. However, clinical applications of implantable microelectrodes remain limited given the challenges of maintaining neuronal signals for extended periods of time and with multiple biological mechanisms negatively affecting electrode performance. Acute and chronic inflammation, oxidative stress, and blood brain barrier disruption contribute to inconsistent electrode performance. We hypothesized that therapeutic hypothermia (TH) applied at the microelectrode insertion site will positively modulate both inflammatory and apoptotic pathways, promoting neuroprotection and improved performance in the long-term.

APPROACH

A custom device and thermoelectric system were designed to deliver controlled TH locally to the cortical implant site at the time of microelectrode array insertion and immediately following surgery. The TH paradigm was derived from in vivo cortical temperature measurements and finite element modeling of temperature distribution profiles in the cortex. Male Sprague-Dawley rats were implanted with non-functional Utah microelectrodes arrays (UMEA) consisting of 4 × 4 grid of 1.5 mm long parylene-coated silicon shanks. In one group, TH was applied to the implant site for two hours following the UMEA implantation, while the other group was implanted under normothermic conditions without treatment. At 48 h, 72 h, 7 d and 14 d post-implantation, mRNA expression levels for genes associated with inflammation and apoptosis were compared between normothermic and hypothermia-treated groups.

MAIN RESULTS

The custom system delivered controlled TH to the cortical implant site and the numerical models confirmed that the temperature decrease was confined locally. Furthermore, a one-time application of TH post UMEA insertion significantly reduced the acute inflammatory response with a reduction in the expression of inflammatory regulating cytokines and chemokines.

SIGNIFICANCE

This work provides evidence that acutely applied hypothermia is effective in significantly reducing acute inflammation post intracortical electrode implantation.

Changes in Physiological and Pathological Behaviours Produced by Deep Microelectrode Implantation Surgery in Rats: A Temporal Analysis

Physiological behaviours such as the sleep-wake cycle and exploratory behaviours are important parameters in intact and sham-operated animals and are usually thought to be unaffected by experimental protocols in which neurosurgery is performed. However, there is insufficient evidence in the literature on the behavioural and cognitive effects observed after deep microelectrode implantation surgery in animal models of neurological diseases. Similarly, in studies that utilize animal models of neurological diseases, the impact of surgery on the pathological phenomena being studied is often minimized. Based on these considerations, we performed a temporal analysis of the effects of deep microelectrode implantation surgery in the hippocampus of rats on quiet wakefulness, sleep, and exploratory activity and the pathological behaviours such as convulsive seizures according to the Racine scale. Male Wistar rats (210-300 g) were used and grouped in sham and epileptic animals. Single doses of pilocarpine hydrochloride (2.4 mg/2 μl; i.c.v.) were administered to the animals to generate spontaneous and recurrent seizures. Deep microelectrode implantation surgeries in both groups and analysis of Fast ripples were performed. Physiological and pathological behaviours were recorded through direct video monitoring of animals (24/7). Our principal findings showed that in epileptic animals, one of the main behaviours affected by surgery is sleep; as a consequence of this behavioural change, a decrease in exploratory activity was also found as well as the mean time spent daily in seizures of scale 4 and the number of seizure events of scales 4 and 5 was increased after surgery. No significant correlations between the occurrence of FR and seizure events of scale 4 (rho 0.63, p value 0.25) or 5 (rho -0.7, p value 0.18) were observed. In conclusion, microelectrode implantation surgeries modified some physiological and pathological behaviours; therefore, it is important to consider this fact when it is working with animal models.

Differential expression of genes involved in the acute innate immune response to intracortical microelectrodes

Higher order tasks in development for brain-computer interfacing applications require the invasiveness of intracortical microelectrodes. Unfortunately, the resulting inflammatory response contributes to the decline of detectable neural signal. The major components of the neuroinflammatory response to microelectrodes have been well-documented with histological imaging, leading to the identification of broad pathways of interest for its inhibition such as oxidative stress and innate immunity. To understand how to mitigate the neuroinflammatory response, a more precise understanding is required. Advancements in genotyping have led the development of new tools for developing temporal gene expression profiles. Therefore, we have meticulously characterized the gene expression profiles of the neuroinflammatory response to mice implanted with non-functional intracortical probes. A time course of differential acute expression of genes of the innate immune response were compared to naïve sham mice, identifying significant changes following implantation. Differential gene expression analysis revealed 22 genes that could inform future therapeutic targets. Particular emphasis is placed on the largest changes in gene expression occurring 24 h post-implantation, and in genes that are involved in multiple innate immune sets including Itgam, Cd14, and Irak4. STATEMENT OF SIGNIFICANCE: Current understanding of the cellular response contributing to the failure of intracortical microelectrodes has been limited to the evaluation of cellular presence around the electrode. Minimal research investigating gene expression profiles of these cells has left a knowledge gap identifying their phenotype. This manuscript represents the first robust investigation of the changes in gene expression levels specific to the innate immune response following intracortical microelectrode implantation. To understand the role of the complement system in response to implanted probes, we performed gene expression profiling over acute time points from implanted subjects and compared them to no-surgery controls. This manuscript provides valuable insights into inflammatory mechanisms at the tissue-probe interface, thus having a high impact on those using intracortical microelectrodes to study and treat neurological diseases and injuries.

Microtubule destabilization caused by silicate via HDAC6 activation contributes to autophagic dysfunction in bone mesenchymal stem cells

BACKGROUND

Silicon-modified biomaterials have been extensively studied in bone tissue engineering. In recent years, the toxicity of silicon-doped biomaterials has gradually attracted attention but requires further elucidation. This study was designed to explore whether high-dose silicate can induce a cytotoxicity effect in bone mesenchymal stem cells (BMSCs) and the role of autophagy in its cytotoxicity and mechanism.

METHODS

Morphologic changes and cell viability of BMSCs were detected after different doses of silicate exposure. Autophagic proteins (LC3, p62), LC3 turnover assay, and RFP-GFP-LC3 assay were applied to detect the changes of autophagic flux following silicate treatment. Furthermore, to identify the potential mechanism of autophagic dysfunction, we tested the acetyl-α-tubulin protein level and histone deacetylase 6 (HDAC6) activity after high-dose silicate exposure as well as the changes in microtubule and autophagic activity after HDAC6 siRNA was applied.

RESULTS

It was found that a high dose of silicate could induce a decrease in cell viability; LC3-II and p62 simultaneously increased after high-dose silicate exposure. A high concentration of silicate could induce autophagic dysfunction and cause autophagosomes to accumulate via microtubule destabilization. Results showed that acetyl-α-tubulin decreased significantly with high-dose silicate treatment, and inhibition of HDAC6 activity can restore microtubule structure and autophagic flux.

CONCLUSIONS

Microtubule destabilization caused by a high concentration of silicate via HDAC6 activation contributed to autophagic dysfunction in BMSCs, and inhibition of HDAC6 exerted a cytoprotection effect through restoration of the microtubule structure and autophagic flux.

Blood-brain barrier disruption and inflammation reaction in mice after chronic exposure to Microcystin-LR

Microcystin-leucine-arginine (MC-LR), which produced by toxic cyanobacteria and widely present in eutrophic waters, has been shown to have potent acute hepatotoxicity. MC-LR has been revealed to inflict damage to brain, while the neurotoxicity of chronic exposure to MC-LR and mechanisms underlying it are still confusing. Here, the mice were exposed to MC-LR dissolved in drinking water at dose of 1, 7.5, 15, and 30 μg/L for consecutive 180 days. MC-LR accumulated in mouse brains and impaired the blood-brain barrier by inducing the expression of matrix metalloproteinase-8 (MMP-8), which was regulated by NF-κB, c-Fos and c-Jun. Furthermore, MC-LR exposure induced microglial and astrocyte activation and resultant neuroinflammatory response. This study highlights the risks to human health of the current microcystin exposure.

A Critical Review of Microelectrode Arrays and Strategies for Improving Neural Interfaces

Though neural interface systems (NISs) can provide a potential solution for mitigating the effects of limb loss and central nervous system damage, the microelectrode array (MEA) component of NISs remains a significant limiting factor to their widespread clinical applications. Several strategies can be applied to MEA designs to increase their biocompatibility. Herein, an overview of NISs and their applications is provided, along with a detailed discussion of strategies for alleviating the foreign body response (FBR) and abnormalities seen at the interface of MEAs and the brain tissue following MEA implantation. Various surface modifications, including natural/synthetic surface coatings, hydrogels, and topography alterations, have shown to be highly successful in improving neural cell adhesion, reducing gliosis, and increasing MEA longevity. Different MEA surface geometries, such as those seen in the Utah and Michigan arrays, can help alleviate the resultant FBR by reducing insertion damage, while providing new avenues for improving MEA recording performance and resolution. Increasing overall flexibility of MEAs as well as reducing their stiffness is also shown to reduce MEA induced micromotion along with FBR severity. By combining multiple different properties into a single MEA, the severity and duration of an FBR postimplantation can be reduced substantially.

High Concentration of Sodium Metasilicate Impairs Autophagic Flux and Induces Apoptosis in Human Umbilical Vein Endothelial Cells

Silicon-doped materials have been widely used in bone regeneration research; however, a consensus on the safety range of silicon ions has not been reached and its toxicity mechanism remains to be further elucidated. This study aims to explore whether high level of sodium metasilicate can induce toxicity effect in human umbilical vein endothelial cells (HUVEC) and the role of autophagy and apoptosis in its toxic mechanism. HUVEC was treated with different level of high silicon and then investigated with respect to morphologic change, cell viability, immunofluorescence, the level of autophagy, and apoptosis-related protein. Moreover, bafilomycin A1 (Baf A1) was applied to detect whether autophagic flux is disrupted, and 3-methyladenine (3-MA, an autophagy inhibitor) was used to determine the relationship between autophagy and apoptosis. Results demonstrated that high-level silicon induced cell viability to decrease; LC3-II, p62, and apoptosis-related proteins were up-regulated after exposure to high-dose silicon (sodium metasilicate concentration more than 1 mM). There is no significant difference in LC3-II and p62 between Baf A1 and sodium metasilicate-exposed group. Besides, 3-MA further increased the apoptotic rate by inhibiting autophagy after high silicon exposure. Collectively, high concentration of silicon can impair autophagy and induce apoptosis in human umbilical vein endothelial cells, and autophagy may play a protective role in HUVEC apoptosis. Furthermore, silicon concentration used in HUVEC should not be more than 1 mM.

Understanding the Role of Innate Immunity in the Response to Intracortical Microelectrodes

Intracortical microelectrodes exhibit enormous potential for researching the nervous system, steering assistive devices and functional electrode stimulation systems for severely paralyzed individuals, and augmenting the brain with computing power. Unfortunately, intracortical microelectrodes often fail to consistently record signals over clinically useful periods. Biological mechanisms, such as the foreign body response to intracortical microelectrodes and self-perpetuating neuroinflammatory cascades, contribute to the inconsistencies and decline in recording performance. Unfortunately, few studies have directly correlated microelectrode performance with the neuroinflammatory response to the implanted devices. However, of those select studies that have, the role of the innate immune system remains among the most likely links capable of corroborating the results of different studies, across laboratories. Therefore, the overall goal of this review is to highlight the role of innate immunity signaling in the foreign body response to intracortical microelectrodes and hypothesize as to appropriate strategies that may become the most relevant in enabling brain-dwelling electrodes of any geometry, or location, for a range of clinical applications.

Boosting often overlooked long wavelength emissions of rare-earth nanoparticles for NIR-II fluorescence imaging of orthotopic glioblastoma

Rare-earth nanoparticles (RE NPs) with narrow long wavelength emissions have been recently investigated for their potential application for fluorescence imaging in the second near-infrared window (NIR-II). Previously these RE NPs have a very limited application in the diagnosis and treatment of deep-seated tumors such as brain tumors, due to their weak fluorescence in the range of 1300-1700 nm. Herein, we report a significant enhancement of more than 10 times regular emission of NaNdF₄ nanoparticles at 1340 nm wavelength by coating them with an inert layer of NaLuF₄, followed by sensitizing with a near-infrared dye (IR-808). We deliver these highly bright nanoparticles into the brain by using focused ultrasound to temporarily open the blood-brain barrier (BBB), and then detect the orthotopic glioblastoma by fluorescence imaging at 1340 nm. The images obtained from long wavelength fluorescence (i.e. 1340 nm) exhibited better resolution and contrast compared to the short wavelength fluorescence (i.e. 1060 nm). Our study not only provides insights for enhancing often overlooked emissions of rare-earth nanoparticles for NIR-II fluorescence imaging of deep-seated tumors, but also demonstrates great potential of focused ultrasound based technology in delivering nanotheranostic agents.

Tissue Response to Neural Implants: The Use of Model Systems Toward New Design Solutions of Implantable Microelectrodes

The development of implantable neuroelectrodes is advancing rapidly as these tools are becoming increasingly ubiquitous in clinical practice, especially for the treatment of traumatic and neurodegenerative disorders. Electrodes have been exploited in a wide number of neural interface devices, such as deep brain stimulation, which is one of the most successful therapies with proven efficacy in the treatment of diseases like Parkinson or epilepsy. However, one of the main caveats related to the clinical application of electrodes is the nervous tissue response at the injury site, characterized by a cascade of inflammatory events, which culminate in chronic inflammation, and, in turn, result in the failure of the implant over extended periods of time. To overcome current limitations of the most widespread macroelectrode based systems, new design strategies and the development of innovative materials with superior biocompatibility characteristics are currently being investigated. This review describes the current state of the art of in vitro, ex vivo, and in vivo models available for the study of neural tissue response to implantable microelectrodes. We particularly highlight new models with increased complexity that closely mimic in vivo scenarios and that can serve as promising alternatives to animal studies for investigation of microelectrodes in neural tissues. Additionally, we also express our view on the impact of the progress in the field of neural tissue engineering on neural implant research.

Bioactive Neuroelectronic Interfaces

Within the neural engineering field, next-generation implantable neuroelectronic interfaces are being developed using biologically-inspired and/or biologically-derived materials to improve upon the stability and functional lifetime of current interfaces. These technologies use biomaterials, bioactive molecules, living cells, or some combination of these, to promote host neuronal survival, reduce the foreign body response, and improve chronic device-tissue integration. This article provides a general overview of the different strategies, milestones, and evolution of bioactive neural interfaces including electrode material properties, biological coatings, and "decoration" with living cells. Another such biohybrid approach developed in our lab uses preformed implantable micro-tissue featuring long-projecting axonal tracts encased within carrier biomaterial micro-columns. These so-called "living electrodes" have been engineered with carefully tailored material, mechanical, and biological properties to enable natural, synaptic based modulation of specific host circuitry while ultimately being under computer control. This article provides an overview of these living electrodes, including design and fabrication, performance attributes, as well as findings to date characterizing in vitro and in vivo functionality.

Restraint Stress Induced Hyperpermeability and Damage of the Blood-Brain Barrier in the Amygdala of Adult Rats

Intense or prolonged exposure to stress can damage various brain structures, including the amygdala and hippocampus, which are associated with emotional-cognitive functions. Furthermore, this deterioration has been linked to a myriad of neurodegenerative and psychiatric disorders, in particular through disruption of the blood-brain barrier (BBB). However, insights remain scarce concerning the effects and mechanisms associated with stress on the BBB in the amygdala. This study explored the effects of restraint stress on the permeability and integrity of the BBB in the amygdala of male adult SD rats. Serum levels of corticosterone (CORT) and S100B were determined through ELISA. The permeability of the BBB was assessed by measuring Evans Blue (EB) leakage in tissue samples from the rats’ amygdala. These samples were immunostained for markers of tight junctions (Claudin-5, Occludin, ZO-1) and adherens junctions (VE-cadherin), as well as GLUT-1 and AQP-4. Staining was evaluated through confocal microscopy, and the level of expression of these proteins was quantified using the Western Blot (WB) technique. The ultrastructure of brain microvascular endothelial cells was assessed with transmission electron microscopy. Moreover, interleukin-1 beta (IL-1β) content in serum and amygdalar tissues were determined by employing ELISA. Exposure to restraint stress was associated with higher serum levels of S100B and EB leakage in amygdala tissues, especially in days 14 and 21 of the experiment, indicating increased permeability of the BBB. After restraint stress, significant decreases in protein expression were detected for tight junctions, adherens junctions and GLUT-1, while a significant increase was observed for AQP-4. The variation trends of fluorescence intensity generally paralleled these results. Following restraint stress, transmission electron microscopy ascertained enlarged gaps in tight junctions and thickened basal membranes in amygdalar capillaries. In addition, increased IL-1β contents in serum and amygdalar tissues were observed in the restraint-stressed groups. These findings suggest that restraint stress mediates time-dependent alterations in the permeability of the BBB, with modifications in the expression of proteins from tight junctions and adherens junctions, as well as ultrastructural changes in brain microvascular endothelial cells. And it was associated with the inflammation. These alterations may be associated with behavioral and cognitive dysfunctions and neurodegenerative disorders.

Developing Next-generation Brain Sensing Technologies - A Review

Advances in sensing technology raise the possibility of creating neural interfaces that can more effectively restore or repair neural function and reveal fundamental properties of neural information processing. To realize the potential of these bioelectronic devices, it is necessary to understand the capabilities of emerging technologies and identify the best strategies to translate these technologies into products and therapies that will improve the lives of patients with neurological and other disorders. Here we discuss emerging technologies for sensing brain activity, anticipated challenges for translation, and perspectives for how to best transition these technologies from academic research labs to useful products for neuroscience researchers and human patients.

Neuroinflammation, oxidative stress, and blood-brain barrier (BBB) disruption in acute Utah electrode array implants and the effect of deferoxamine as an iron chelator on acute foreign body response

The use of intracortical microelectrode arrays has gained significant attention in being able to help restore function in paralysis patients and study the brain in various neurological disorders. Electrode implantation in the cortex causes vasculature or blood-brain barrier (BBB) disruption and thus elicits a foreign body response (FBR) that results in chronic inflammation and may lead to poor electrode performance. In this study, a comprehensive insight into the acute molecular mechanisms occurring at the Utah electrode array-tissue interface is provided to understand the oxidative stress, neuroinflammation, and neurovascular unit (astrocytes, pericytes, and endothelial cells) disruption that occurs following microelectrode implantation. Quantitative real time polymerase chain reaction (qRT-PCR) was used to quantify the gene expression at acute time-points of 48-hr, 72-hr, and 7-days for factors mediating oxidative stress, inflammation, and BBB disruption in rats implanted with a non-functional 4 × 4 Utah array in the somatosensory cortex. During vascular disruption, free iron released into the brain parenchyma can exacerbate the FBR, leading to oxidative stress and thus further contributing to BBB degradation. To reduce the free iron released into the brain tissue, the effects of an iron chelator, deferoxamine mesylate (DFX), was also evaluated.

The role of inflammation on the functionality of intracortical microelectrodes

OBJECTIVE

Neuroinflammation has long been associated with the performance decline of intracortical microelectrodes (IMEs). Consequently, several strategies, including the use of anti-inflammatories, have been employed to mitigate the inflammation surrounding IMEs. However, these strategies have had limited success towards achieving a chronically viable cortical neural interface, questioning the efficacy of anti-inflammatory approach.

APPROACH

Herein, we conducted a systematic study in rats implanted with functional devices by modulating inflammation via systemic injection of lipopolysaccharide (LPS), dexamethasone (DEX), a combination of both, or none to assess the degree of inflammation on device functionality. We hypothesized that implanted rats treated with LPS will have a negative impact, and rats treated with DEX will have a positive impact on functionality IMEs and histological outcome.

MAIN RESULTS

Contrary to our hypothesis, we did not observe adverse effects in recording metrics among different groups with LPS and/or DEX treatment despite alterations in initial pro-inflammatory markers. We also did not observe any functional benefit of anti-inflammatory treatment. Regardless of the treatment conditions, the recording quality degraded at chronic time points. In end-point histology, implanted rats that received LPS had significantly lower NeuN density and higher levels of CD68 surrounding the implant site, indicative of the pro-inflammatory effect of LPS, which, however, contradicted with the recorded results.

SIGNIFICANCE

Collectively, our results suggest that acute inflammatory events may not be the key driver for functional degradation of IMEs. Future intervention strategies geared towards improving the functional longevity of intracortical devices may benefit using multi-modal approaches rather than a single approach, such as controlling the initial inflammatory response.