Biology subjects

Shoffstall, A. J.

Publications and source records attributed to Shoffstall, A. J..

12 recordsLinked to original sources

bioRxiv2025

Micro-CT Analysis of a Needle to Nerve Approach for Interfascicular Peripheral Nerve Stimulation in Porcine Nerves

MotivationPeripheral nerve interfaces typically have a tradeoff between selectivity and invasiveness. Interfascicular interfaces placed within the peripheral nerve, but outside of the fascicles preserving the perineurium are a promising avenue in balancing this tradeoff. This study quantifies electrode placement using novel tools designed to deliver flexible microwires interfascicularly in a porcine model. MethodsSeven Yorkshire pigs were implanted with Minimally invasive interfascicular Nerve Stimulation (MiiNS) arrays in the nerves of the brachial plexus resulting in a total of ten implanted nerve samples. High-resolution micro-computed tomography (micro-CT) of implanted nerves stained with phosphotungistic acid (PTA) showed contact placement relative to fascicular anatomy and all other contacts. The analysis also examined the relationship between microwire trajectory angle and fascicle traversal. Further, in a subset of samples (n=4), hematoxylin and eosin (H&E) histological analysis was performed after micro-CT imaging. These histological images were coregistered with the micro-CT to validate the positional information of the micro-CT. ResultsAcross the 56 total MiiNS microwire placements, 84% were interfascicular, while 16% were intrafascicular, characterized by traversal through a fascicle. Contacts were broadly distributed throughout the nerves cross section and the majority (79%) were in the central half of the nerves cross section (R>0.707), with no evidence of angular clustering in any single direction. On average, nearest neighbor distances between contacts measured 2256.26{+/-}1760.28 {micro}m in 3D and 730.71 {+/-}564.83 {micro}m transversely, with implants spanning 10.3 {+/-} 4.3 mm along length of nerve. The angle of wire trajectory into the nerve was correlated with fascicle traversal, with steeper angles of insertion associated with more instances of fascicle traversal. Histological analysis corroborated the fascicular borders and wire placements found on micro-CT and demonstrated perineurium integrity. SignificanceInterfascicular implantation can reliably access both central and distributed regions of the nerve, while not being confined to a single plane, enabling access to regions which have been historically challenging to stimulate effectively. The observed nearest-neighbor transverse spacing between contacts is within the range of reported ideal values for selective activation. The MiiNS placement characteristics show its potential as an effective peripheral nerve interface alternative which achieves distributed contact placement, including in the center of the nerve volume, while remaining predominantly outside of the perineurium.

bioengineering↗

bioRxiv2025

Mapping the Fascicular Morphology and Organization of the Human Sciatic Nerve via High-Resolution MicroCT Imaging

ObjectiveImplanted neuroprostheses can restore standing and walking after spinal cord injury and somatosensation after limb loss. Yet current approaches often fail to reliably activate hamstring muscles crucial for upright stability and mobility or to target afferent fibers for sensory restoration. We developed a novel methodology using high-resolution micro-computed tomography (microCT) to visualize and track fascicle groups innervating distinct hamstring muscles along the human sciatic nerve. This approach provides a framework for mapping fascicular topography in complex neural pathways to optimize standing neuroprostheses. MethodsBilateral sciatic nerves were dissected and excised from an embalmed human cadaver, annotated with branch names, and stained with phosphotungstic acid before undergoing microCT scanning at 11.4 m isotropic resolution. Images were segmented with a 3D U-Net convolutional neural network. Segmentation results were used to quantify morphological metrics and track fascicular organization along [~]25 cm of the nerve. MicroCT reconstructions were validated against histological cross sections. ResultsGross dissection revealed matched proximal-to-distal branching between left and right sciatic nerves: branch to long head of the biceps femoris (lhBF), branch to hamstring part of the adductor magnus and semimembranosus (HAM/SM), and branch to semitendinosus (ST). All branches originated medially and followed an inferomedial trajectory. Branch-free lengths of the sciatic exhibited asymmetry, especially between the lumbosacral roots to the first branch (5.5 cm left vs. 1.5 cm right) and lhBF to the HAM/SM branch (9.0 cm left vs. 16.5 cm right). MicroCT analysis revealed bilateral symmetry in fascicle diameters ([~]0.4 mm) and total fascicle counts ([~]84) but asymmetry in hamstring-innervating fascicle counts (left [~]7, right: [~]9). The 3D fascicular maps revealed that hamstring fascicles were located in the anteromedial portion of the sciatic nerve cross section and remained separate for distances up to 15.9 cm proximal to their branching points. SignificanceOur microCT-based approach enables efficient, high-resolution 3D mapping of fascicular organization within large, complex peripheral nerves like the sciatic nerve, overcoming previous technical limitations. This methodology informs development of neuroprostheses with improved hamstring muscle activation for enhanced standing function.

bioengineering↗

bioRxiv2025

Automated 3D Segmentation of Human Vagus Nerve Fascicles and Epineurium from Micro-Computed Tomography Images Using Anatomy-Aware Neural Networks

ObjectivePrecise segmentation and quantification of nerve morphology from imaging data are critical for designing effective and selective peripheral nerve stimulation (PNS) therapies. However, prior studies on nerve morphology segmentation suffer from important limitations in both accuracy and efficiency. This study introduces a deep learning approach for robust and automated 3D segmentation of human vagus nerve fascicles and epineurium from high-resolution micro-computed tomography (microCT) images. MethodsWe developed a multi-class 3D U-Net to segment fascicles and epineurium that incorporates a novel anatomy-aware loss function to ensure that predictions respect nerve topology. We trained and tested the network using subject-level five-fold cross-validation with 100 microCT sub-volumes (11.4 m isotropic resolution) from cervical and thoracic vagus nerves stained with phosphotungstic acid from five subjects. We benchmarked the 3D U-Nets performance against a 2D U-Net using both standard and anatomy-specific segmentation metrics. ResultsOur 3D U-Net generated high-quality segmentations (average Dice similarity coefficient: 0.93). Compared to the 2D U-Net, our 3D U-Net yielded significantly better volumetric overlap, boundary delineation, and fascicle-level accuracy. The 3D approach reduced anatomical errors by 2.5-fold, provided more consistent inter-slice boundaries, and improved detection of fascicle splits/merges by nearly 6-fold. SignificanceOur automated 3D segmentation pipeline provides anatomically accurate 3D maps of peripheral neural morphology from microCT data. The automation allows for high throughput, and the substantial improvement in segmentation quality and anatomical fidelity enhances the reliability of morphological analysis, vagal pathway mapping, and the implementation of realistic computational models. These advancements provide a foundation for understanding the functional organization of the vagus and other peripheral nerves and optimizing PNS therapies.

neuroscience↗

bioRxiv2025

Impact of infusion conditions and anesthesia on CSF tracer dynamics in mouse brain

Tracer imaging has been instrumental in mapping the brains solute transport pathways facilitated by cerebrospinal fluid (CSF) flow. However, the impact of tracer infusion parameters on CSF flow remains incompletely understood. This study evaluated the influence of infusion location, rate, and anesthetic regimens on tracer transport using dynamic contrast-enhanced MRI with Gd-DTPA as a CSF tracer. Infusion rate effects were assessed by administering Gd-DTPA into the cisterna magna (ICM) at two rates under isoflurane anesthesia. Anesthetic effects were evaluated by comparing transport patterns between isoflurane and ketamine/xylazine (K/X) anesthesia at the slower rate. Gd-DTPA transport was also examined after lateral ventricle (ICV) infusion, the primary site of CSF production. The results demonstrate that, besides anesthesia, both the location and rate of infusion substantially affected solute transport within the brain. ICV infusion led to rapid, extensive transport into deep brain regions, while slower ICM infusion resulted in more pronounced transport to dorsal brain regions. Cross-correlation and hierarchical clustering analyses of region-specific Gd-DTPA signal time courses revealed that ICM infusion facilitated transport along periarterial spaces, while ICV infusion favored transport across the ventricular-parenchymal interface. These findings underscore the importance of experimental conditions in influencing tracer kinetics and spatial distribution in the brain.

physiology↗

bioRxiv2023

Computational modeling of dorsal root ganglion stimulation using an Injectrode

ObjectiveMinimally invasive neuromodulation therapies like the Injectrode, which is composed of a tightly wound polymer-coated platinum/iridium microcoil, offer a low-risk approach for administering electrical stimulation to the dorsal root ganglion (DRG). This flexible electrode is aimed to conform to the DRG. The stimulation occurs through a transcutaneous electrical stimulation (TES) patch, which subsequently transmits the stimulation to the Injectrode via a subcutaneous metal collector. However, effectiveness of stimulation relies on the specific geometrical configurations of the Injectrode-collector-patch system. Hence, there is a need to investigate which design parameters influence the activation of targeted neural structures. ApproachWe employed a hybrid computational modeling approach to analyze the impact of the Injectrode system design parameters on charge delivery and the neural response to stimulation. We constructed multiple finite element method models of DRG stimulation and multi-compartment models of DRG neurons. We simulated the neural responses using parameters based on prior acute preclinical experiments. Additionally, we developed multiple human-scale computational models of DRG stimulation to investigate how design parameters like Injectrode size and orientation influenced neural activation thresholds. Main resultsOur findings were in accordance with acute experimental measurements and indicated that the Injectrode system predominantly engages large-diameter afferents (A{beta}-fibers). These activation thresholds were contingent upon the surface area of the Injectrode. As the charge density decreased due to increasing surface area, there was a corresponding expansion in the stimulation amplitude range before triggering any pain-related mechanoreceptor (A{delta}-fibers) activity. SignificanceThe Injectrode demonstrates potential as a viable technology for minimally invasive stimulation of the DRG. Our findings indicate that utilizing a larger surface area Injectrode enhances the therapeutic margin, effectively distinguishing the desired A{beta} activation from the undesired A{delta}-fiber activation.

bioengineering↗

bioRxiv2022

Spatially selective stimulation of the pig vagus nerve to modulate target effect versus side effect

Electrical stimulation of the cervical vagus nerve using implanted electrodes (VNS) is FDA-approved for the treatment of drug-resistant epilepsy, treatment-resistant depression, and most recently, chronic ischemic stroke rehabilitation. However, VNS is critically limited by the unwanted stimulation of nearby neck muscles - a result of non-specific stimulation activating motor nerve fibers within the vagus. Prior studies suggested that precise placement of small epineural electrodes can modify VNS therapeutic effects, such as cardiac responses. However, it remains unclear if placement can alter the balance between intended effect and limiting side effect. We used an FDA investigational device exemption approved six-contact epineural cuff to deliver VNS in pigs and quantified how epineural electrode location impacts on- and off-target VNS activation. Detailed post-mortem histology was conducted to understand how the underlying neuroanatomy impacts observed functional responses. Here we report the discovery and characterization of clear neuroanatomy-dependent differences in threshold and saturation for responses related to both effect (change in heart rate) and side effect (neck muscle contractions). The histological and electrophysiological data were used to develop and validate subject-specific computation models of VNS, creating a well-grounded quantitative framework to optimize electrode location-specific activation of nerve fibers governing intended effect versus unwanted side effect.

bioengineering↗

bioRxiv2021

Fascicles split or merge every ~560 microns within the human cervical vagus nerve

1Vagus nerve stimulation (VNS) is FDA approved for stroke rehabilitation, epilepsy, and depression; however, the vagus functional anatomy underlying the implant is poorly understood. We used microCT to quantify fascicular structure and neuroanatomy within human cervical vagus nerves. Fascicles split or merged every ~560 m (17.8 {+/-} 6.1 events/cm). The high degree of fascicular splitting and merging in humans may explain the clinical heterogeneity in patient responses.

neuroscience↗

bioRxiv2021

Augmented Transcutaneous Stimulation Using an Injectable Electrode

Minimally invasive neuromodulation technologies seek to marry the neural selectivity of implantable devices with the low-cost and non-invasive nature of transcutaneous electrical stimulation (TES). The Injectrode(R) is a needle-delivered electrode that is injected onto neural structures under image guidance. Power is then transcutaneously delivered to the Injectrode using surface electrodes. The Injectrode serves as a low-impedance conduit to guide current to the deep on-target nerve, reducing activation thresholds by an order of magnitude compared to using only surface stimulation electrodes. To minimize off-target recruitment of cutaneous fibers, the energy transfer efficiency from the surface electrodes to the Injectrode must be optimized. TES energy is transferred to the Injectrode through both capacitive and resistive mechanisms. Electrostatic finite element models generally used in TES research consider only the resistive means of energy transfer by defining tissue conductivities. Here, we present an electroquasistatic model, taking into consideration both the conductivity and permittivity of tissue, to understand transcutaneous power delivery to the Injectrode. The model was validated with measurements taken from (n=4) swine cadavers. We used the validated model to investigate system and anatomic parameters that influence the coupling efficiency of the Injectrode energy delivery system. Our work suggests the relevance of electroquasistatic models to account for capacitive charge transfer mechanisms when studying TES, particularly when high-frequency voltage components are present, such as those used for voltage-controlled pulses and sinusoidal nerve blocks.

bioengineering↗

bioRxiv2020

In vivo visualization of pig vagus nerve 'vagotopy' using ultrasound

BackgroundPlacement of the clinical vagus nerve stimulating cuff is a standard surgical procedure based on anatomical landmarks, with limited patient specificity in terms of fascicular organization or vagal anatomy. As such, the therapeutic effects are generally limited by unwanted side effects of neck muscle contractions, demonstrated by previous studies to result from stimulation of 1) motor fibers near the cuff in the superior laryngeal and 2) motor fibers within the cuff projecting to the recurrent laryngeal. ObjectiveThe use of patient-specific visualization of vagus nerve fascicular organization could better inform clinical cuff placement and improve clinical outcomes. MethodsThe viability of ultrasound, with the transducer in the surgical pocket, to visualize vagus nerve fascicular organization (i.e. vagotopy) was characterized in a pig model. Ultrasound images were matched to post-mortem histology to confirm the utility of ultrasound in identifying fascicular organization. ResultsHigh-resolution ultrasound accurately depicted the vagotopy of the pig vagus nerve intra-operatively, as confirmed via histology. The stereotypical pseudo-unipolar cell body aggregation at the nodose ganglion was identifiable, and these sensory afferent fascicular bundles were traced down the length of the vagus nerve. Additionally, the superior and recurrent laryngeal nerves were identified via ultrasound. ConclusionsIntraoperative visualization of vagotopy and surrounding nerves using ultrasound is a novel approach to optimize stimulating cuff placement, avoid unwanted activation of motor nerve fibers implicated in off-target effects, and seed patient-specific models of vagal fiber activation to improve patient outcomes.

neuroscience↗

bioRxiv2020

Sources of Off-Target Effects of Vagus Nerve Stimulation Using the Helical Clinical Lead in Domestic Pigs

Clinical data suggest that efficacious vagus nerve stimulation (VNS) is limited by side effects such as cough and dyspnea that have stimulation thresholds lower than those for therapeutic outcomes. VNS side effects are putatively caused by activation of nearby muscles within the neck, via direct muscle activation or activation of nerve fibers innervating those muscles. Our goal was to determine the thresholds at which various VNS-evoked effects occur in the domestic pig--an animal model with vagus anatomy similar to human--using the bipolar helical lead deployed clinically. Intrafascicular electrodes were placed within the vagus nerve to record electroneurographic (ENG) responses, and needle electrodes were placed in the vagal-innervated neck muscles to record electromyographic (EMG) responses. Contraction of the cricoarytenoid muscle occurred at low amplitudes ([~]0.3 mA) and resulted from activation of motor nerve fibers in the cervical vagus trunk within the electrode cuff which bifurcate into the recurrent laryngeal branch of the vagus. At higher amplitudes ([~]1.4 mA), contraction of the cricoarytenoid and cricothyroid muscles was generated by current leakage outside the cuff to activate motor nerve fibers running within the nearby superior laryngeal branch of the vagus. Activation of these muscles generated artifacts in the ENG recordings that may be mistaken for compound action potentials representing slowly conducting A{delta}-, B-, and C-fibers. Our data resolve conflicting reports of the stimulation amplitudes required for C-fiber activation in large animal studies (>10 mA) and human studies (<250 {micro}A). After removing muscle-generated artifacts, ENG signals with post-stimulus latencies consistent with A{delta}- and B-fibers occurred in only a small subset of animals, and these signals had similar thresholds to those that caused bradycardia. By identifying specific neuroanatomical pathways that cause off-target effects and characterizing the stimulation dose-response curves for on- and off-target effects, we hope to guide interpretation and optimization of clinical VNS.

neuroscience↗

bioRxiv2019

Functional Vagotopy in the Cervical Vagus Nerve of the Domestic Pig: Implications for Vagus Nerve Stimulation

Given current clinical interest in vagus nerve stimulation, there are surprisingly few studies characterizing the anatomy of the vagus nerve in large animal models as it pertains to on-and off-target engagement of local fibers. We sought to address this gap by evaluating vagal anatomy in the domestic pig, whose vagus nerve organization and size approximates the human cervical vagus nerve. We provide data on key features across the cervical vagus nerve including diameter, number and diameter of fascicles, and distance of fascicles from the epineural surface where stimulating electrodes are placed. We also characterized the relative locations of the superior and recurrent laryngeal branches of the vagus nerve that have been implicated in therapy limiting side effects with common electrode placement. We identified key variants across the cohort that may be important for vagus nerve stimulation with respect to changing sympathetic/parasympathetic tone, such as cross-connections to the sympathetic trunk. We discovered that cell bodies of pseudo-unipolar cells aggregate together to form a very distinct grouping within the nodose ganglion. This distinct grouping gives rise to a larger number of smaller fascicles as one moves caudally down the cervical vagus nerve. This often leads to a distinct bimodal organization, or vagotopy that may be advantageous to exploit in design of electrodes/stimulation paradigms. Finally, we placed our data in context of historic and recent histology spanning mouse, rat, canine, pig, non-human primate and human models, thus providing a comprehensive resource to understand similarities and differences across species.

neuroscience↗

bioRxiv2019

A Truly Injectable Neural Stimulation Electrode Made From an In-Body Curing Polymer/Metal Composite

Implanted neural stimulation and recording devices hold vast potential to treat a variety of neurological conditions, but the invasiveness, complexity, and cost of the implantation procedure greatly reduce access to an otherwise promising therapeutic approach. To address this need, we have developed a novel electrode that begins as an uncured, flowable pre-polymer that can be injected around a neuroanatomical target to minimize surgical manipulation. Referred to as the Injectrode, the electrode conforms to target structures forming an electrically conductive interface which is orders of magnitude less stiff than conventional neuromodulation electrodes. To validate the Injectrode, we performed detailed electrochemical and microscopy characterization of its material properties and validated the feasibility of using it to electrically stimulate the nervous system in rats and swine. The silicone-metal-particle composite performed very similarly to pure wire of the same metal (silver) in all measures, including exhibiting a favorable cathodic charge storage capacity (CSCC) and charge injection limits compared to the clinical LivaNova stimulation electrode and silver wire electrodes. By virtue of being simpler than traditional electrode designs, less invasive, and more cost-effective, the Injectrode has the potential to increase the adoption of neuromodulation therapies for existing and new indications.

bioengineering↗