Work-related muscle disorders are a main cause of missed work, globally, and arecostly for public health systems. However, development of musculoskeletal tissue diagnostics is lagging compared to other tissues and organs. Myofascial trigger points (MTP) are unique muscle tissue phenomenon that are challenging to address due to a lack of objective assessment methodology. This study seeks to meet this need by devising a non-invasive, objective methodology for evaluating musculoskeletal tissue following intervention or physical provocation, specific to the anterior forearm region. In Aim 1, current literature on MTP pathophysiology informs a multi-modal assessment approach, including: 1) pain pressure threshold (PPT), 2) power Doppler (PD) ultrasound, 3) strain elastography (SE), and 4) surface electromyography (sEMG). In Aim 2, controlled ultrasound image acquisition and standardization techniques are developed for imaging muscle tissue with PD (Aim 2a) and SE (Aim 2b) . These techniques improved differentiability of vascularity and compliance estimation after physical provocation or intervention. In Aim 3, the multi-modal approach is implemented in a human pilot study (n=34) investigating MTP response to osteopathic manipulative treatment, compared to rest and light exercise. Positive trends and significant changes are detected after OMT and rest. PPT significantly increased after OMT (p = 0.021). Tissue compliance significantly increase after rest (p ≪ 0.0001) and after OMT( p = 0.002). Principal component analysis finds 9 of 13 outcome measures to be salient features of MTP treatment effect. The data suggests high and low responders, yielding insights for improved patient screening and study design for future work. With further optimization and development, this method may be applied to a broad array of clinical scenarios for musculoskeletal tissue evaluation directed towards amelioration of neuromuscular symptoms.

A reliable method for real-time blood flow monitoring in vivo is critical for several medical applications, including monitoring cardiovascular diseases, evaluating interventional procedures and surgeries, and increasing the safety and efficacy of neuromodulation procedures. High-speed methods are particularly necessary for neural monitoring, due to the brain's heightened sensitivity to hypoxic and ischemic conditions. High-speed CBF monitoring methods may also provide a useful biomarker for the development of a closed-loop deep brain stimulation (DBS) system. Current methods such as laser Doppler, bold fMRI, and positron emission tomography (PET) often involve cumbersome instrumentation and are therefore not well- suited for chronic microvasculature monitoring. The purpose of this study is to develop a method for real-time measurement of blood flow changes using electrochemical impedance spectra (EIS). Utilizing EIS to measure CBF has the potential to be included in a chronic, closed-loop DBS system that is modulated by fluctuations in CBF, using minimal additional instrumentation. Five experiments in rodents were conducted, with the objective of 1) determining whether electrochemical impedance spectra showed impedance changes correlated with changes in blood flow, assessing the sensitivity, specificity, and limitations of detection of this method, and 2) determining whether cyclic voltammetry-based method could be used to produce EIS more rapidly than current methods. The experimental set-up included electrodes in the femoral artery with the administration of endothelin (ET-1) to induce blood flow changes (N=1), electrodes in the motor cortex using isoflurane variation to induce blood flow changes (N=3), and electrodes in the femoral artery with the administration of nitroglycerin (NTG) to induce blood flow changes (N=1). Preliminary results suggest that impedance changes in the higher frequencies (over 160 Hz) demonstrated higher sensitivity to blood flow changes in the femoral artery model compared to <100 Hz frequencies, with inconclusive results in the motor cortex model. Future in vivo experiments will be conducted using endothelin-1 to further establish the relationship between impedance and cerebral blood flow in the brain.

Neurological disorders are the leading cause of physical and cognitive declineglobally and affect nearly 15% of the current worldwide population. These disorders include, but are not limited to, epilepsy, Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis. With the aging population, an increase in the prevalence of neurodegenerative disorders is expected. Electrophysiological monitoring of neural signals has been the gold standard for clinicians in diagnosing and treating neurological disorders. However, advances in detection and stimulation techniques have paved the way for relevant information not seen by standard procedures to be captured and used in patient treatment. Amongst these advances have been improved analysis of higher frequency activity and the increased concentration of alternative biomarkers, specifically pH change, during states of increased neural activity. The design and fabrication of devices with the ability to reliably interface with the brain on multiple scales and modalities has been a significant challenge. This dissertation introduces a novel, concentric, multi-scale micro-ECoG array for neural applications specifically designed for seizure detection in epileptic patients. This work investigates simultaneous detection and recording of adjacent neural tissue using electrodes of different sizes during neural events. Signal fidelity from electrodes of different sizes during in vivo experimentation are explored and analyzed to highlight the advantages and disadvantages of using varying electrode sizes. Furthermore, the novel multi-scale array was modified to perform multi-analyte detection experiments of pH change and electrophysiological activity on the cortical surface during epileptic events. This device highlights the ability to accurately monitor relevant information from multiple electrode sizes and concurrently monitor multiple biomarkers during clinical periods in one procedure that typically requires multiple surgeries.

The field of non-invasive neurostimulation techniques offer promising avenues for the treatment of various neurological and psychiatric disorders such as Parkinson's disease, migraines, chronic pain, and epilepsy. The proposed work is a novel technique for the production of high-end ultrasonic forces by interaction of gigahertz electromagnetic radiations for the purpose of neural modulation. These ultrasonic forces are created in dielectric materials such as cell membranes by the electrostrive effect, providing a potential new neurotherapeutic technique. The ability for this technique to provide neurostimulatory effects was investigated using in vitro studies of neuronal cultures and in vivo studies on sciatic nerves. Direct exposure of E18 rat cortical neurons to these EM radiations demonstrated changes in cellular membrane potential, suggesting effects could be potentially similar to direct electrical stimulation. An exploration of neuromodulatory effects to rat sciatic nerves indicates exposure produces changes to peak-to-peak muscular response. These findings suggest promising results for this new potential neuromodulation modality.

For patients with focal drug-resistant epilepsy, surgical remediation can be a hopeful last resort treatment option, but only if enough clinical signs can point to an epileptogenic tissue region. Subdural grids offer ample cortical surface area coverage to evaluate multiple regions of interest, yet they lack the spatial resolution typical of penetrating electrodes. Additionally, subthreshold stimulation through subdural grids is a stable source for detecting eloquent cortex surrounding potential epileptic tissue. Researchers have each tried introducing microelectrodes to increase the spatial resolution but ran into connectivity challenges as the desired surface area increased. Meanwhile, clinical hybrid options have shown promise by combining multiple electrode sizes, maintaining surface area coverage with an increased spatial resolution where necessary. However, a benchtop method to quantify spatial resolution or test signal summation, without the complexity of an in vivo study, has not been found in the literature; a subdural grid in gel solution has functioned previously but without a published method. Thus, a novel hybrid electrode array with a telescopic configuration including three electrode geometries, called the M$^3$ array, is proposed to maintain cortical surface area coverage and provide spatial clarity in regions of interest using precision microfabrication techniques. Electrophysiological recording with this array should enhance the clinical signal portfolio without changing how clinicians interface with the broad surface data from macros. Additionally, this would provide a source for simultaneous recording and stimulation from the same location due to the telescopic nature of the design. A novel benchtop test method should remove complexity from in vivo tests while allowing direct comparison of recording capabilities of different cortical surface electrodes. Implementing the proposed M$^3$ electrode array in intracranial monitoring improves the current technology without much compromise, enhancing patient outcomes, reducing risks, and encouraging swift clinical translation.

Neural tissue is a delicate system comprised of neurons and their synapses, glial cells for support, and vasculature for oxygen and nutrient delivery. This complexity ultimately gives rise to the human brain, a system researchers have become increasingly interested in replicating for artificial intelligence purposes. Some have even gone so far as to use neuronal cultures as computing hardware, but utilizing an environment closer to a living brain means having to grapple with the same issues faced by clinicians and researchers trying to treat brain disorders. Most outstanding among these are the problems that arise with invasive interfaces. Optical techniques that use fluorescent dyes and proteins have emerged as a solution for noninvasive imaging with single-cell resolution in vitro and in vivo, but feeding in information in the form of neuromodulation still requires implanted electrodes. The implantation process of these electrodes damages nearby neurons and their connections, causes hemorrhaging, and leads to scarring and gliosis that diminish efficacy. Here, a new approach for noninvasive neuromodulation with high spatial precision is described. It makes use of a combination of ultrasound, high frequency acoustic energy that can be focused to submillimeter regions at significant depths, and electric fields, an effective tool for neuromodulation that lacks spatial precision when used in a noninvasive manner. The hypothesis is that, when combined in a specific manner, these will lead to nonlinear effects at neuronal membranes that cause cells only in the region of overlap to be stimulated. Computational modeling confirmed this combination to be uniquely stimulating, contingent on certain physical effects of ultrasound on cell membranes. Subsequent in vitro experiments led to inconclusive results, however, leaving the door open for future experimentation with modified configurations and approaches. The specific combination explored here is also not the only untested technique that may achieve a similar goal.

Safety and efficacy of neuromodulation are influenced by abiotic factors like failure of implants, biotic factors like tissue damage, and molecular and cellular mechanisms of neuromodulation. Accelerated lifetime test (ALT) predict lifetime of implants by accelerating failure modes in controlled bench-top conditions. Current ALT models do not capture failure modes involving biological mechanisms. First part of this dissertation is focused on developing ALTs for predicting failure of chronically implanted tungsten stimulation electrodes. Three factors used in ALT are temperature, H2O2 concentration, and amount of charge delivered through electrode to develop a predictive model of lifetime for stimulation electrodes. Second part of this dissertation is focused on developing a novel method for evaluating tissue response to implants and electrical stimulation. Current methods to evaluate tissue damage in the brain require invasive and terminal procedures that have poor clinical translation. I report a novel non-invasive method that sampled peripheral blood monocytes (PBMCs) and used enzyme-linked immunoassay (ELISA) to assess level of glial fibrillary acidic protein (GFAP) expression and fluorescence-activated cell sorting (FACS) to quantify number of GFAP expressing PBMCs. Using this method, I was able to detect and quantify GFAP expression in PBMCs. However, there was no statistically significant difference in GFAP expression between stimulatory and non-stimulatory implants. Final part of this dissertation assessed molecular and cellular mechanisms of non-invasive ultrasound neuromodulation approach. Unlike electrical stimulation, cellular mechanisms of ultrasound-based neuromodulation are not fully known. Final part of this dissertation assessed role of mechanosensitive ion channels and neuronal nitric oxide production in cell cultures under ultrasound excitation. I used fluorescent imaging to quantify expression of nitric oxide in neuronal cell cultures in response to ultrasound stimulation. Results from these experiments indicate that neuronal nitric oxide production increased in response to ultrasound stimulation compared to control and decreased when mechanosensitive ion channels were suppressed. Two novel methods developed in this dissertation enable assessment of lifetime and safety of neuromodulation techniques that use electrical stimulation through implants. The final part of this dissertation concludes that non-invasive ultrasound neuromodulation may be mediated through neuronal nitric oxide even in absence of activation of mechanosensitive ion channels.

Breast cancer can be imaged at greater depths using photoacoustic imaging to differentiate between cancerous and non-cancerous tissue. Current photoacoustic modalities struggle to display images in real-time because of the required image reconstruction. In this work, we aim to create a real-time photoacoustic imaging system where the photoacoustic effect is detected through changes in index of refraction. To reach this aim, two methods are applied to visualize the acoustic waves including Schlieren optics and differential interference contrast microscopy. This combined approach provides a new tool for the widespread application in clinical settings.