Biology subjects

Cullen, D. K.

Publications and source records attributed to Cullen, D. K..

At least 19 recordsLinked to original sources

bioRxiv2026

Long-Term Functional and Histological Outcomes Following Sutureless Peripheral Nerve Repair Using Nerve Tape in Pigs

Severe peripheral nerve injuries result in incomplete recovery despite neurorrhaphy. Microsurgical suturing is technically demanding, time-intensive, and may produce variable fascicular alignment. Nerve Tape is an FDA-approved sutureless device enabling rapid, reproducible nerve coaptation. This study compared Nerve Tape with epineurial microsuturing following common peroneal nerve transection in Yucatan minipigs. Over 12 months, both groups demonstrated reinnervation of the tibialis anterior and extensor digitorum brevis, representing proximal and distal muscle targets, respectively. Tibialis anterior recovery was comparable between groups. In contrast, Nerve Tape produced greater distal motor recovery in the extensor digitorum brevis, with approximately 1.8-fold higher compound muscle action potential amplitude and 74.3% versus 46.0% recovery compared with microsutures. Compound nerve action potential amplitudes recorded from the motor branch of the deep peroneal nerve were also greater with Nerve Tape, whereas conduction velocities were comparable. Histological analysis demonstrated preserved fascicular architecture distal to the repair in both groups, with no significant differences in axon count, mean myelinated axon diameter, or g-ratio in the terminal common peroneal nerve or its distal motor branch. Clinical use was demonstrated in a representative case with progressive recovery. Nerve Tape supported durable structural and functional recovery and improved distal motor reinnervation compared with microsuturing.

neuroscience↗

bioRxiv2026

Boldine inhibits SARM1 NADase Activity and Preserves Axonal Integrity After Nerve Injury

Wallerian degeneration of anucleated axonal segments is driven by SARM1, which depletes axonal NAD+, disrupting energy metabolism and triggering self-destruction. SARM1 inhibition is an emerging therapeutic target for traumatic nerve injuries. Boldine, a natural aporphine alkaloid from Peumus boldus, modulates connexin hemichannels, oxidative stress, and inflammation. Building on our published work showing boldines neuroprotective effects in nerve injury models, we hypothesized that boldine also inhibits SARM1 directly. A fluorescence polarization assay revealed that boldine inhibits SARM1 NADase activity with an IC50 of approximately 7.5 uM. AI-assisted structural modeling (AlphaFold3-based Boltz-1 with GNINA docking) predicted two boldine binding sites on SARM1: the TIR catalytic site (Kd [~] 13.5 uM) and the ARM-TIR regulatory interface (Kd [~] 12 uM). In a sciatic nerve explant model, boldine preserved the integrity of anucleated axonal segments at 3 and 7 days post-transection relative to vehicle controls. These findings suggest boldine may act as a dual-site SARM1 inhibitor and support its development as a neuroprotective therapy after traumatic axonal injury.

neuroscience↗

bioRxiv2026

Increased CD3 Immunoreactive Cells Persist Chronically in the Brain Parenchyma in Association with Focal Cortical Contusion following Experimental TBI

While a history of TBI is associated with an increased risk of neurodegenerative disease, associated mechanisms remain largely unknown. Neuroinflammation is commonly implicated as playing a role in progressive neurodegeneration in general, yet little is known about the adaptive response of neuroinflammation in TBI or how it may contribute to progressive pathologies. To parse out components of the adaptive response, we assessed for intraparenchymal T-cell infiltration in two different translational large animal (swine) models of TBI, inertial injury and focal contusion. We characterized the extent and distribution of T cells post-injury and their association with blood-brain barrier disruption and axonal pathology. T-cell infiltration following focal TBI followed a spatiotemporal progression from gray matter at 72 hours to both gray and white matter at 6 months post-injury, consistent with recruitment into the parenchyma and then white matter. Inertial injury did not lead to substantial T-cell infiltration despite BBB breakdown and axonal pathology. We did not find a spatial correlation between blood-brain barrier breakdown or axonal pathology and T-cell infiltration in focal TBI. These data suggest that there is an active adaptive response to TBI, particularly in tissue proximal to contusions. A large animal model that reproducibly demonstrates chronic T-cell infiltration may allow for examination of the downstream effects of the adaptive response to TBI, and whether targeting this adaptive response may reduce chronic inflammation and improve recovery.

neuroscience↗

bioRxiv2025

Astrocyte Transcriptomics in a Three-Dimensional Tissue-Engineered Rostral Migratory Stream

The glial tube is a longitudinal structure predominantly composed of densely bundled, aligned astrocytes that projects from subventricular zone (SVZ) to olfactory bulb. Neural precursor cells (NPCs) generated in the SVZ migrate through this glial tube - referred to as the rostral migratory stream (RMS) - to replace olfactory bulb interneurons in the mammalian brain. RMS astrocytes have distinct morphological and functional characteristics facilitating their unique purpose as an endogenous living scaffold directing NPC migration and maturation. However, the transcriptomic factors underlying these unique structure-function attributes versus standard stellate astrocytes have not been examined. We previously developed biofabrication techniques to create the first tissue-engineered rostral migratory stream (TE-RMS) that replicates key features of the glial tube in vivo. We have shown that TE-RMS astrocytes exhibit elongated nuclei, longitudinally aligned intermediate filaments, and enrichment of key functional proteins - cytoarchitectural and surface features characteristic of native RMS astrocytes. In the current study, we performed RNAseq on TE-RMS astrocytes in comparison to planar astrocyte cultures to identify gene expression patterns that may underlie their profound morphological and functional differences. Remarkably, we found 4008 differentially expressed genes in TE-RMS astrocytes, with 2076 downregulated (e.g. LOC690251, ccn5) and 1932 upregulated (e.g. lrrc45, cntn1) compared to planar astrocytes. Moreover, there were 256 downregulated and 91 upregulated genes with >3-fold change. We also conducted analyses of gene sets related to cytoskeleton and nuclear structure, revealing greatest enrichment of actin-related components. Overall, the TE-RMS offers a platform to study interplay between transcriptomic and cytoarchitectural dynamics in a unique astrocyte population.

bioengineering↗

bioRxiv2022

Hippocampal Interneuronal Dysfunction and Hyperexcitability in Porcine Model of Concussion

Cognitive impairment is a common symptom following mild traumatic brain injury (mTBI or concussion) and can persist for years in some individuals. Hippocampal slice preparations following closed-head, rotational acceleration injury in swine have previously demonstrated reduced axonal function and hippocampal circuitry disruption. However, electrophysiological changes in hippocampal neurons and their subtypes in a large animal mTBI model have not been examined. Using in vivo electrophysiology techniques, we examined laminar oscillatory field potentials and single unit activity in the hippocampal network 7 days post-injury in anesthetized minipigs. Concussion altered the electrophysiological properties of pyramidal cells and interneurons differently in area CA1. While the firing rate, spike width and amplitude of CA1 interneurons were significantly decreased post-mTBI, these parameters were unchanged in CA1 pyramidal neurons. In addition, CA1 pyramidal neurons in TBI animals were less entrained to hippocampal gamma (40 - 80 Hz) oscillations. Stimulation of the Schaffer collaterals also revealed hyperexcitability across the CA1 lamina post-mTBI. Computational simulations suggest that reported changes in interneuronal physiology may be due to alterations in voltage-gated sodium channels. These data demonstrate that a single concussion can lead to significant neuronal and circuit level changes in the hippocampus, which may contribute to cognitive dysfunction following mTBI.

neuroscience↗

bioRxiv2021

Dopaminergic axon tracts within a hyaluronic acid hydrogel encasement for implantation to restore the nigrostriatal pathway

Parkinsons disease (PD) affects 10 million patients worldwide, making it the second most prevalent neurodegenerative disease. Motor symptoms emerge from the loss of dopamine in the striatum after the death of dopaminergic neurons and the long-projecting axons of the nigrostriatal pathway. Current treatments, such as dopamine replacement, deep brain stimulation or cell therapies, disregard the loss of this pathway at the core of symptoms. We sought to address this by improving our tissue-engineered nigrostriatal pathway (TE-NSP) technology, which consists of a tubular hydrogel with a collagen/laminin core that encases an aggregate of dopaminergic neurons and their axons in a way that resembles the nigrostriatal pathway. These constructs can be implanted to replace the lost neurons and axons with fidelity to the pathway, and thus provide dopamine according to feedback from the host circuitry. While TE-NSPs have been traditionally fabricated with agarose, here we utilized a hyaluronic acid (HA) hydrogel to expand the functionality of the encasement and our control over its properties. Using rat ventral midbrain neurons, we found that TE-NSPs exhibited longer and faster neurite growth with HA relative to agarose, with no differences observed in electrically-evoked dopamine release. When transplanted, HA hydrogels reduced host neuron loss and inflammation around the implant compared to agarose, and the cells and axons within TE-NSPs survived and maintained their cytoarchitecture for at least 2 weeks. HighlightsO_LIWe fabricated engineered dopaminergic axons encased in a tubular hydrogel. C_LIO_LIWe made hydrogels from methacrylated hyaluronic acid and compared them to agarose. C_LIO_LIAxons in HA hydrogels had longer and faster axon growth and displayed evoked dopamine release. C_LIO_LIHA hydrogels reduced the host inflammatory response and supported neuron and axon survival in vivo. C_LIO_LIThis platform may be used to reconstruct the nigrostriatal pathway to treat Parkinsons disease. C_LI

bioengineering↗

bioRxiv2021

Relationships between biomechanical parameters, neurological recovery, and neuropathology following concussion in swine

Mild traumatic brain injury (mTBI) affects millions of individuals annually primarily through falls, traffic collisions, or blunt trauma and can generate symptoms that persist for years. Closed-head rotational injury is the most common form of mTBI and is defined by a rapid change in acceleration within an intact skull. Injury kinematics - the mechanical descriptors of injury-inducing motion - explain movement of the head, energy transfer to the brain, and, therefore, determine injury severity. However, the relationship between closed-head rotational injury kinematics - such as angular velocity, angular acceleration, and injury duration - and outcome after mTBI is currently unknown. To address this gap in knowledge, we analyzed archived surgical records of 24 swine experiencing a diffuse closed-head rotational acceleration mTBI against 12 sham animals. Kinematics were contrasted against acute recovery outcomes, specifically apnea, extubation time, standing time, and recovery duration. Compared to controls, animals with mTBI were far more likely to have apnea (p<0.001) along with shorter time to extubation (p=0.023), and longer time from extubation to recovery (p=0.006). Using regression analyses with variable selection, we generated simplified linear models relating kinematics to apnea (R2=0.27), standing time (R2=0.39) and recovery duration (R2=0.42). Neuropathology was correlated with multiple kinematics, with maximum acceleration exhibiting the strongest correlation (R2=0.66). Together, these data suggest the interplay between multiple injury kinematics, including minimum velocity and middle to minimum acceleration time, best explain acute recovery parameters and neuropathology after mTBI in swine. Future experiments that independently manipulate individual kinematics could be instrumental in developing translational diagnostics for clinical mTBI.

neuroscience↗

bioRxiv2020

Diverse Changes in Microglia Morphology and Axonal Pathology Over One Year after Mild Traumatic Brain Injury in Pigs

Over 2.8 million people experience mild traumatic brain injury (TBI) in the United States each year, which may lead to long-term neurological dysfunction. The mechanical forces that occur due to TBI propagate through the brain to produce diffuse axonal injury (DAI) and trigger secondary neuroinflammatory cascades. The cascades may persist from acute to chronic time points after injury, altering the homeostasis of the brain. However, the relationship between the hallmark axonal pathology of diffuse TBI and potential changes in glial cell activation or morphology have not been established in a clinically relevant large animal model at chronic time points. In this study, we assessed tissue from pigs subjected to rapid head rotation in the coronal plane to generate mild TBI. Neuropathological assessments for axonal pathology, microglial morphological changes, and astrocyte reactivity were conducted in specimens out to 1 year post injury. We detected an increase in overall amyloid precursor protein pathology, as well as periventricular white matter and fimbria/fornix pathology after a single mild TBI. We did not detect changes in corpus callosum integrity or astrocyte reactivity. However, detailed microglial skeletal analysis revealed changes in morphology, most notably increases in the number of microglial branches, junctions, and endpoints. These subtle changes were most evident in periventricular white matter and certain hippocampal subfields, and were observed out to 1 year post injury in some cases. These ongoing morphological alterations suggest persistent change in neuroimmune homeostasis. Additional studies are needed to characterize the underlying molecular and neurophysiological alterations, as well as potential contributions to neurological deficits.

pathology↗

bioRxiv2020

Tyrosine-Derived Polycarbonate Nerve Guidance Tubes Elicit Pro-Regenerative Extracellular Matrix Deposition When Used to Bridge Segmental Nerve Defects in Swine

Promising biomaterials should be tested in appropriate large animal models that recapitulate human inflammatory and regenerative responses. Previous studies have shown tyrosine-derived polycarbonates (TyrPC) are versatile biomaterials with a wide range of applications across multiple disciplines. The library of TyrPC has been well studied and consists of thousands of polymer compositions with tunable mechanical characteristics and degradation and resorption rates that are useful for nerve guidance tubes (NGTs). NGTs made of different TyrPCs have been used in segmental nerve defect models in small animals. The current study is an extension of this work and evaluates NGTs made using two different TyrPC compositions in a 1 cm porcine peripheral nerve repair model. We first evaluated a nondegradable TyrPC formulation, demonstrating proof-of-concept chronic regenerative efficacy up to 6 months with similar nerve/muscle electrophysiology and morphometry to the autograft repair control. Next, we characterized the acute regenerative response using a degradable TyrPC formulation. After 2 weeks in vivo, TyrPC NGT promoted greater deposition of pro-regenerative extracellular matrix (ECM) constituents (in particular collagen I, collagen III, collagen IV, laminin and fibronectin) compared to commercially available collagen-based NGTs. This corresponded with dense Schwann cell infiltration and axon extension across the lumen. These findings confirmed results reported previously in a mouse model and reveal that TyrPC NGTs were well tolerated in swine and facilitated host axon regeneration and Schwann cell infiltration in the acute phase across segmental defects - likely by eliciting a favorable neurotrophic ECM milieu. This regenerative response ultimately can contribute to functional recovery.

bioengineering↗

bioRxiv2019

Peripheral Nerve Repair Using Tissue Engineered Living Scaffolds Comprised of Stretch-Grown Aligned Axonal Tracts Promotes Survival of Spinal Cord Motor Neurons

Peripheral nerve injury (PNI) impacts millions annually, often leaving debilitated patients with minimal repair options to improve functional recovery. Our group has previously developed tissue engineered nerve grafts (TENGs) featuring long, aligned axonal tracts from dorsal root ganglia (DRG) neurons that are fabricated in custom bioreactors using the process of axon "stretch-growth". We have shown that TENGs effectively serve as "living scaffolds" to promote regeneration across segmental nerve defects by exploiting the newfound mechanism of axon-facilitated axon regeneration, or "AFAR", by simultaneously providing haptic and neurotrophic support. To extend this work, the current study investigated the efficacy of living versus non-living regenerative scaffolds in preserving host sensory and motor neuronal health following nerve repair. Rats were assigned across five groups: naive, or repair using autograft, nerve guidance tube (NGT) with collagen, NGT + non-aligned DRG populations in collagen, or TENGs. We found that TENG repairs yielded equivalent regenerative capacity as autograft repairs based on preserved health of host spinal cord motor neurons and acute axonal regeneration, whereas NGT repairs or DRG neurons within an NGT exhibited reduced motor neuron preservation and diminished regenerative capacity. These acute regenerative benefits ultimately resulted in enhanced levels of functional recovery in animals receiving TENGs, at levels matching those attained by autografts. Our findings indicate that TENGs may preserve host spinal cord motor neuron health and regenerative capacity without sacrificing an otherwise uninjured nerve (as in the case of the autograft), and therefore represent a promising alternative strategy for neurosurgical repair following PNI. HIGHLIGHTSO_LITENGs preserve host spinal cord motor neuron health and regenerative capacity acutely following repair of segmental nerve defects, matching that of the clinical gold-standard autograft and exceeding commercially-available nerve guidance tubes. C_LIO_LITENGs facilitated regeneration across segmental nerve defects, yielding similar degree of chronically surviving host spinal motor neurons and functional recovery as compared to autografts. C_LIO_LIEarly surgical intervention for segmental nerve defect with living scaffolds, such as TENGs and autografts, preserves the host regenerative capacity, and likely increases the ceiling for total regeneration and functional recovery at chronic time points compared to (acellular) commercially-available nerve guidance tubes. C_LIO_LITENGs preserve host neuronal health and regenerative capacity without sacrificing an otherwise uninjured nerve, and therefore represent a promising alternative strategy to autografts or nerve guidance tube repairs. C_LI

bioengineering↗

bioRxiv2019

Non-Genetic Reprogramming of Monocytes via Microparticle Phagocytosis for Sustained Modulation of Macrophage Phenotype

Monocyte-derived macrophages orchestrate tissue regeneration by homing to sites of injury, phagocytosing pathological debris, and stimulating other cell types to repair the tissue. Accordingly, monocytes have been investigated as a translational and potent source for cell therapy, but their utility has been hampered by their rapid acquisition of a pro-inflammatory phenotype in response to the inflammatory injury microenvironment. To overcome this problem, we designed a cell therapy strategy where we collect and exogenously reprogram monocytes by intracellularly loading the cells with biodegradable microparticles containing an anti-inflammatory drug in order to modulate and maintain an anti-inflammatory phenotype over time. To test this concept, poly(lactic-co-glycolic) acid microparticles were loaded with the anti-inflammatory drug dexamethasone (Dex) and administered to primary human monocytes for four hours to facilitate phagocytic uptake. After removal of non-phagocytosed microparticles, microparticle-loaded monocytes differentiated into macrophages and stored the microparticles intracellularly for several weeks in vitro, releasing drug into the extracellular environment over time. Cells loaded with intracellular Dex microparticles showed decreased expression and secretion of inflammatory factors even in the presence of pro-inflammatory stimuli up to 7 days after microparticle uptake compared to untreated cells or cells loaded with blank microparticles. This study represents a new strategy for long-term maintenance of anti-inflammatory macrophage phenotype using a translational monocyte-based cell therapy strategy without the use of genetic modification. Because of the ubiquitous nature of monocyte-derived macrophage involvement in pathology and regeneration, this strategy holds potential as a treatment for a vast number of diseases and disorders.

bioengineering↗

bioRxiv2019

Tissue Engineered Axon Tracts Serve as Living Scaffolds to Accelerate Axonal Regeneration and Functional Recovery Following Peripheral Nerve Injury in Rats

Although regeneration of damaged axons in peripheral nerves has long been observed, the mechanisms facilitating this growth are not well characterized. Recently, we demonstrated that host axon regeneration could be greatly enhanced by transplanting engineered living axon tracts to guide outgrowth. Here, we used a model of rat sciatic nerve transection to explore potential mechanisms of this facilitated regeneration and its efficacy in comparison with nerve guidance tubes (NGTs) and autografts. Tissue engineered nerve grafts (TENGs) were developed via \"stretch-growth\" in mechanobioreactors and consisted of centimeter-scale aligned axonal tracts. Either TENGs, NGTs or autografts (reversed nerve) were then transplanted to bridge a 1 cm segmental gap in the sciatic nerve with the mechanisms of axonal regrowth assessed at 2 weeks and the extent of functional recovery assessed at 16 weeks. We observed numerous host axons growing directly along and intertwining with pre-formed axonal tracts in TENGs. This behavior appears to mimic the action of \"pioneer\" axons in developmental pathfinding by providing living cues for directed and accelerated outgrowth. Indeed, we found that the rates of axon regeneration were 3-4 fold faster than NGTs and equivalent to autografts. It was also observed that infiltration of host Schwann cells - traditional drivers of peripheral axon regeneration - was both accelerated and progressed directly along TENG axonal tracts. These TENG repairs resulted in levels of functional recovery equivalent to autografts, with each being several fold superior to NGT repairs. This new mechanism - which we term \"axon-facilitated axon-regeneration\" - may be further exploited to enhance axonal regeneration and functional recovery following neurotrauma.

bioengineering↗

bioRxiv2019

A Porcine Model of Peripheral Nerve Injury Enabling Ultra-Long Regenerative Distances: Surgical Approach, Recovery Kinetics, and Clinical Relevance

Approximately 20 million Americans currently experience residual deficits from traumatic peripheral nerve injury. Despite recent advancements in surgical technique, peripheral nerve repair typically results in poor functional outcomes due to prolonged periods of denervation resulting from long regenerative distances coupled with relatively slow rates of axonal regeneration. Development of novel surgical solutions requires valid preclinical models that adequately replicate the key challenges of clinical peripheral nerve injury. Our team has developed a porcine model using Yucatan minipigs that provides an opportunity to investigate peripheral nerve regeneration using different nerves tailored for a specific mechanism of interest, such as (1) nerve modality: motor, sensory, and mixed-modality; (2) injury length: short versus long gap; and (3) total regenerative distance: proximal versus distal injury. Here, we describe a comprehensive porcine model of two challenging clinically relevant procedures for repair of long segmental lesions ([≥] 5 cm) - the deep peroneal nerve repaired using a sural nerve autograft and the common peroneal nerve repaired using a saphenous nerve autograft - each featuring ultra-long total regenerative distances (up to 20 cm and 27 cm, respectively) to reach distal targets. This paper includes a detailed characterization of the relevant anatomy, surgical approach/technique, functional/electrophysiological outcomes, and nerve morphometry for baseline and autograft repaired nerves. These porcine models of major peripheral nerve injury are suitable as preclinical, translatable models for evaluating the efficacy, safety, and tolerability of next-generation artificial nerve grafts prior to clinical deployment.

neuroscience↗

bioRxiv2019

\"Stretch-Growth\" of Motor Axons in Custom Mechanobioreactors to Generate Long-Projecting Axonal and Axonal-Myocyte Constructs

The central feature of peripheral motor axons is their remarkable lengths as they project from a motor neuron residing in the spinal cord to an often-distant target muscle. However, to date in vitro models have not replicated this central feature owing to challenges in generating motor axon tracts beyond a few millimeters in length. To address this, we have developed a novel combination of micro-tissue engineering and mechanically assisted growth techniques to create long-projecting centimeter-scale motor axon tracts. Here, primary motor neurons were isolated from the spinal cords of rats and induced to form engineered micro-spheres via forced aggregation in custom micro-wells. This three-dimensional micro-tissue yielded healthy motor neurons projecting dense, fasciculated axonal tracts. Within our custom-built mechanobioreactors, motor neuron culture conditions, neuronal/axonal architecture, and mechanical growth conditions were systematically optimized to generate parameters for robust and efficient \"stretch-growth\" of motor axons. We found that axons projecting from motor neuron aggregates were able to respond to axon displacement rates at least 10 times greater than that tolerated by axons projecting from dissociated motor neurons. The growth and structural characteristics of these stretch-grown motor axons were compared to benchmark stretch-grown axons from sensory dorsal root ganglion neurons, revealing similar axon densities yet increased motor axon fasciculation. Finally, motor axons were integrated with myocytes and then stretch-grown to create novel long-projecting axonal-myocyte constructs that better recreate characteristic dimensions of native nerve-muscle anatomy. This is the first demonstration of mechanical elongation of spinal cord motor axons and may have applications as anatomically inspired in vitro testbeds or as tissue engineered \"living scaffolds\" for targeted axon tract reconstruction following nervous system injury or disease.\n\nSignificance StatementWe have developed novel axon tracts of unprecedented lengths spanning either two discrete populations of neurons or a population of neurons and skeletal myocytes. This is the first demonstration of \"stretch-grown\" motor axons that recapitulate the structure of spinal motor neurons in vivo by projecting long axons from a pool of motor neurons to distant targets, and may have applications as anatomically inspired in vitro test beds to study mechanisms of axon growth, development, and neuromuscular function in anatomically accurate axo-myo constructs; as well as serve as \"living scaffolds\" in vivo for targeted axon tract reconstruction following nervous system trauma.

bioengineering↗

bioRxiv2018

Multichannel Silicon Probes for Laminar Cortical and Hippocampal Recordings in Large Animals.

Decoding laminar information across deep brain structures and cortical regions is necessary in order to understand the spatiotemporal ensembles that represent cognition and memory. Large animal models are essential for translational research due to their gyrencephalic neuroanatomy and significant white matter composition. One of the major obstacles to applying the approaches currently utilized in lower order animals are technical limitations in silicon probes, specifically a lack of long-length probes with appropriate stiffness to penetrate to deeper structures with minimal damage to the neural interface. We tested various solutions and designs of multichannel silicon probes developed for large animal electrophysiology by recording neurophysiological signals from deep laminar structures in an acute preparation and in chronically implanted awake behaving Yucatan pigs. Electrophysiological parameters of single units and local field potentials were analyzed to evaluate performance over time of given silicon probes in chronic implantations. The cross-sectional area of silicon probes was found to be a crucial determinant of silicon probes single unit performance over time, potentially due to reduction of damage to the neural interface. EDGE-style probes had the highest yields during intra-hippocampal recordings in pigs, making them the most suitable for chronic implantations and awake behavioral experimentation. Novel CAMB 64-channel EDGE-style probes with linear and poly-2 site arrangement tested acutely had optimal single unit separation and a denser sampling of the laminar structure, identifying them as potential candidates for chronic implantations with less cortical damage above the active portion of the probe. This study provides an analysis of multichannel silicon probes designed for large animal laminar electrophysiology of deep brain structures, and suggests that current designs are reaching the physical thresholds necessary for long-term (~ 1 month) recordings from laminar deep structures with single-unit resolution.

neuroscience↗

bioRxiv2018

Cardiac myocyte microtissue aggregates broadcast local field potentials

Muscle tissue has been exploited as a living biopotential amplifier to facilitate transduction of peripheral nerve signals into prosthetic control in patients with limb amputation. Here we sought to address the question of whether microscopically small volumes of muscle tissue could effectively broadcast field potentials to electrodes not immediately in contact with that tissue. Cardiac myocytes were grown as three-dimensional aggregates containing 105 cells comprising a volume of approximately 0.065 mm3 (~500 m in diameter) atop multi-electrode arrays. In addition to the expected spontaneous contraction potentials detected using electrodes in direct contact with the myocytes, potentials could also be detected on distant electrodes not contacting the aggregates. Specifically, while both dissociated and aggregated cardiac myocyte cultures generated spontaneous contractions that could easily be recorded from underlying multi-electrode arrays, only aggregated myocyte cultures generated signals detectable several millimeters away by the electrode grid floating in media. This confirmed the ability of micro-volumes of aggregated muscle tissue to broadcast readily detectible signals. The amplitude of the potentials generated by the aggregates decreased exponentially with distance. The aggregates were sensitive to pharmacologic modification with isoproterenol increasing contraction rate. Simultaneous recordings with electrodes in physical contact to the aggregate and with electrodes several millimeters away revealed that the aggregates function as amplifiers and low-pass filters. This study lays the groundwork for forging myocyte aggregates as \"living amplifiers\" for long-term neural recording in brain-computer interfaces to treat neurological disease and injury.

bioengineering↗

bioRxiv2018

A Computational Model of Bidirectional Axonal Growth in Micro-Tissue Engineered Neuronal Networks (micro-TENNs)

Micro-Tissue Engineered Neural Networks (Micro-TENNs) are living three-dimensional constructs designed to replicate the neuroanatomy of white matter pathways in the brain, and are being developed as implantable microtissue for axon tract reconstruction or as anatomically-relevant in vitro experimental platforms. Micro-TENNs are composed of discrete neuronal aggregates connected by bundles of long-projecting axonal tracts within miniature tubular hydrogels. In order to help design and optimize micro-TENN performance, we have created a new computational model including geometric and functional properties. The model is built upon the three-dimensional diffusion equation and incorporates large-scale uni- and bi-directional growth that simulates realistic neuron morphologies. The model captures unique features of 3D axonal tract development that are not apparent in planar outgrowth, and may be insightful for how white matter pathways form during brain development. The processes of axonal outgrowth, branching, turning and aggregation/bundling from each neuron are described through functions built on concentration equations and growth time distributed across the growth segments. Once developed we conducted multiple parametric studies to explore the applicability of the method and conducted preliminary validation via comparisons to experimentally grown micro-TENNs for a range of growth conditions. Using this framework, this model can be applied to study micro-TENN growth processes and functional characteristics using spiking network or compartmental network modeling. This model may be applied to improve our understanding of axonal tract development and functionality, as well as to optimize the fabrication of implantable tissue engineered brain pathways for nervous system reconstruction and/or modulation.

bioengineering↗

bioRxiv2018

Optically-Controlled \"Living Electrodes\" with Long-Projecting Axon Tracts for a Synaptic Brain-Machine Interface

Achievements in intracortical neural interfaces are compromised by limitations in specificity and long-term performance. A biological intermediary between devices and the brain may offer improved specificity and longevity through natural synaptic integration with deep neural circuitry, while being accessible on the brain surface for optical read-out/control. Accordingly, we have developed the first "living electrodes" comprised of implantable axonal tracts protected within soft hydrogel cylinders for the biologically-mediated monitoring/modulation of brain activity. Here we demonstrate the controlled fabrication, rapid axonal outgrowth, reproducible cytoarchitecture, and simultaneous optical stimulation and recording of neuronal activity within these engineered constructs in vitro. We also present their transplantation, survival, integration, and optical recording in rat cortex in vivo as a proof-of-concept for this neural interface paradigm. The creation and functional validation of these preformed, axon-based "living electrodes" is a critical step towards developing a new class of biohybrid neural interfaces to probe and modulate native circuitry.

bioengineering↗