James P. Harris

A Porcine Model of Traumatic Brain Injury via Head Rotational Acceleration

Unique from other brain disorders, traumatic brain injury (TBI) generally results from a discrete biomechanical event that induces rapid head movement. The large size and high organization of the human brain makes it particularly vulnerable to traumatic injury from rotational accelerations that can cause dynamic deformation of the brain tissue. Therefore, replicating the injury biomechanics of human TBI in animal models presents a substantial challenge, particularly with regard to addressing brain size and injury parameters. Here we present the historical development and use of a porcine model of head rotational acceleration. By scaling up the rotational forces to account for difference in brain mass between swine and humans, this model has been shown to produce the same tissue deformations and identical neuropathologies found in human TBI. The parameters of scaled rapid angular accelerations applied for the model reproduce inertial forces generated when the human head suddenly accelerates or decelerates in falls, collisions, or blunt impacts. The model uses custom-built linkage assemblies and a powerful linear actuator designed to produce purely impulsive non-impact head rotation in different angular planes at controlled rotational acceleration levels. Through a range of head rotational kinematics, this model can produce functional and neuropathological changes across the spectrum from concussion to severe TBI. Notably, however, the model is very difficult to employ, requiring a highly skilled team for medical management, biomechanics, neurological recovery, and specialized outcome measures including neuromonitoring, neurophysiology, neuroimaging, and neuropathology. Nonetheless, while challenging, this clinically relevant model has proven valuable for identifying mechanisms of acute and progressive neuropathologies as well as for the evaluation of noninvasive diagnostic techniques and potential neuroprotective treatments following TBI.

Rapid neuroinflammatory response localized to injured neurons after diffuse traumatic brain injury in swine

&NA; Despite increasing appreciation of the critical role that neuroinflammatory pathways play in brain injury and neurodegeneration, little is known about acute microglial reactivity following diffuse traumatic brain injury (TBI) — the most common clinical presentation that includes all concussions. Therefore, we investigated acute microglial reactivity using a porcine model of closed‐head rotational velocity/acceleration‐induced TBI that closely mimics the biomechanical etiology of inertial TBI in humans. We observed rapid microglial reactivity within 15 min of both mild and severe TBI. Strikingly, microglial activation was restrained to regions proximal to individual injured neurons – as denoted by trauma‐induced plasma membrane disruption – which served as epicenters of acute reactivity. Single‐cell quantitative analysis showed that in areas free of traumatically permeabilized neurons, microglial density and morphology were similar between sham or following mild or severe TBI. However, microglia density increased and morphology shifted to become more reactive in proximity to injured neurons. Microglial reactivity around injured neurons was exacerbated following repetitive TBI, suggesting further amplification of acute neuroinflammatory responses. These results indicate that neuronal trauma rapidly activates microglia in a highly localized manner, and suggest that activated microglia may rapidly influence neuronal stability and/or pathophysiology after diffuse TBI. HighlightsMicroglia responded to localized neuronal injury within minutes of closed‐head TBI.Rapid activation was only appreciable in regions exhibiting permeabilized neurons.Microglia reactivity was exacerbated following repetitive TBI.This gyrencephalic injury model closely replicates biomechanics of clinical TBI.Acute inflammation may influence pathophysiology following concussion in humans.

The Evolution of Neuroprosthetic Interfaces.

The ideal neuroprosthetic interface permits high-quality neural recording and stimulation of the nervous system while reliably providing clinical benefits over chronic periods. Although current technologies have made notable strides in this direction, significant improvements must be made to better achieve these design goals and satisfy clinical needs. This article provides an overview of the state of neuroprosthetic interfaces, starting with the design and placement of these interfaces before exploring the stimulation and recording platforms yielded from contemporary research. Finally, we outline emerging research trends in an effort to explore the potential next generation of neuroprosthetic interfaces.

Microscale characterization of a mechanically adaptive polymer nanocomposite with cotton-derived cellulose nanocrystals for implantable BioMEMS

A mechanically adaptive polymer nanocomposite for use as a structural material for microelectromechanical system (MEMS)-based penetrating implantable biosensors, particularly for the brain, is presented as a solution to the limited clinical implementation of such sensors. Micromechanical testing of MEMS-scale test structures was used to determine the Youngs moduli of the polymer nanocomposite in both its dry rigid state (E = 2414 MPa) and its wet compliant state (E = 4.9 MPa), as well as the rate of mechanical switching upon immersion in an aqueous solution. The softening of the composite materials after implantation in the cortex of a Sprague-Dawley rat was studied by ex vivo environmentally controlled microtensile testing. A microfabrication process for producing metallized neural probes for recording of electrical signals was also developed. The results support the mechanically adaptive nanocomposite as a viable option for MEMS-based penetrating implantable biosensors.

A three-dimensional image processing program for accurate, rapid, and semi-automated segmentation of neuronal somata with dense neurite outgrowth

Three-dimensional (3-D) image analysis techniques provide a powerful means to rapidly and accurately assess complex morphological and functional interactions between neural cells. Current software-based identification methods of neural cells generally fall into two applications: (1) segmentation of cell nuclei in high-density constructs or (2) tracing of cell neurites in single cell investigations. We have developed novel methodologies to permit the systematic identification of populations of neuronal somata possessing rich morphological detail and dense neurite arborization throughout thick tissue or 3-D in vitro constructs. The image analysis incorporates several novel automated features for the discrimination of neurites and somata by initially classifying features in 2-D and merging these classifications into 3-D objects; the 3-D reconstructions automatically identify and adjust for over and under segmentation errors. Additionally, the platform provides for software-assisted error corrections to further minimize error. These features attain very accurate cell boundary identifications to handle a wide range of morphological complexities. We validated these tools using confocal z-stacks from thick 3-D neural constructs where neuronal somata had varying degrees of neurite arborization and complexity, achieving an accuracy of ≥95%. We demonstrated the robustness of these algorithms in a more complex arena through the automated segmentation of neural cells in ex vivo brain slices. These novel methods surpass previous techniques by improving the robustness and accuracy by: (1) the ability to process neurites and somata, (2) bidirectional segmentation correction, and (3) validation via software-assisted user input. This 3-D image analysis platform provides valuable tools for the unbiased analysis of neural tissue or tissue surrogates within a 3-D context, appropriate for the study of multi-dimensional cell-cell and cell-extracellular matrix interactions.

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.

Tissue engineered nigrostriatal pathway for treatment of Parkinson's disease

The classic motor deficits of Parkinsons disease are caused by degeneration of dopaminergic neurons in the substantia nigra pars compacta, resulting in the loss of their long‐distance axonal projections that modulate the striatum. Current treatments only minimize the symptoms of this disconnection as there is no approach capable of replacing the nigrostriatal pathway. We are applying microtissue engineering techniques to create living, implantable constructs that mimic the architecture and function of the nigrostriatal pathway. These constructs consist of dopaminergic neurons with long axonal tracts encased within hydrogel microcolumns. Microcolumns were seeded with dopaminergic neuronal aggregates, while lumen extracellular matrix, growth factors, and end targets were varied to optimize cytoarchitecture. We found a 10‐fold increase in axonal outgrowth from aggregates versus dissociated neurons, resulting in remarkable axonal lengths of over 6 mm by 14 days and 9 mm by 28 days in vitro. Axonal extension was also dependent upon lumen extracellular matrix, but did not depend on growth factor enrichment or neuronal end target presence. Evoked dopamine release was measured via fast scan cyclic voltammetry and synapse formation with striatal neurons was observed in vitro. Constructs were microinjected to span the nigrostriatal pathway in rats, revealing survival of implanted neurons while maintaining their axonal projections within the microcolumn. Lastly, these constructs were generated with dopaminergic neurons differentiated from human embryonic stem cells. This strategy may improve Parkinsons disease treatment by simultaneously replacing lost dopaminergic neurons in the substantia nigra and reconstructing their long‐projecting axonal tracts to the striatum.

Extracellular matrix-derived tissues for neurological applications

Nervous system injury and degeneration may result in debilitating conditions that limit quality of life. To facilitate nervous system repair and improve functional outcomes, clinicians and researchers are utilizing therapies that provide proregenerative cues and structural support using exogenous extracellular matrix (ECM) derived neurological implants. These strategies are generally intended to structurally replace excised tissues, facilitate tissue regrowth, aid in hemostasis, and/or assist in the delivery of bioactive substances. ECM-based products offer several distinct advantages over synthetic materials, including bioactivity, active remodeling, and decreased inflammatory and foreign body responses. A range of naturally occurring, ECM-based materials including laminin, collagen, hyaluronic acid, and fibronectin are being applied as biomaterial scaffolds, either alone or augmented with growth factors and/or living cells to promote nervous system repair and regeneration. The chapter presents the current uses of ECM-based neurological implants and future directions in the development of restorative ECM-based biomaterials, constructs, and other implants.

Factitious parotid tumor.

Factitious or self-induced illness can occur as a diagnostic dilemma. We present a case of a patient who injected saliva into the parotid region with a resultant clinical picture consistent with a parotid tumor. A high degree of medical sophistication and a complex underlying psychopathologic behavior in these patients make the diagnosis and treatment difficult. Psychiatric consultation is an integral part of their management.