The stretch reflex circuit is one of the most primitive circuits of mammalian system and serves mainly to control the length of the muscle. It consists of four elements: the stretch sensor (muscle spindle/ intrafusal fiber lie parallel between extrafusal, contractile musculature), extrafusal muscle fiber, sensory neuron and motoneuron. The basic principle of the stretch reflex arc circuit is as follows: whenever there is a sudden stretch in a muscle, it needs to compensate back to its original length so as to prevent any kind of injury. It performs this compensation process using a simple negative feed back circuit called the stretch reflex arc. Any form of stretch in a muscle activates the stretch sensors (muscle spindle/ intrafusal fiber) lying deep in each muscle. After the stretch sensors get activated, it sends a train of signals to the spinal cord through the sensory neurons. The sensory neurons relay this information to the motoneuron. The motoneuron performs the necessary information processing and sends the message to the extrafusal fibers so as to compensate for the sudden stretch action. The motoneuron conveys this message to the extrafusal fibers by communicating through the special synaptic junctions called neuromuscular junctions. Based on this information, the extrafusal fibers act accordingly so as to counter the effect of sudden stretch. This is also called the monosynaptic stretch reflex that involves a single synapse between a sensory neuron and a motoneuron. To date studying these stretch reflex circuits is only feasible in animal models. Almost no effort has been made to tissue engineer such circuits for a better understanding of the complex development and repair processes of the stretch reflex circuit formation. The long-term goal of this research is to tissue engineer a cellular prototype of the entire iii stretch reflex circuit. The specific theme of this dissertation research was to tissue engineer the motoneuron to muscle segment of the stretch reflex arc circuit utilizing micro-fabrication, interface design and defined medium formulations. In order to address this central theme, the following hypothesis has been proposed. The first part of the hypothesis is that microfabrication technology, interface design and defined medium formulations can be effectively combined to tissue engineer the motoneuron to muscle segment of the stretch reflex arc. The second part of the hypothesis is that different growth factors, hormones, nanoparticles, neurotransmitters and synthetic substrate can be optimally utilized to regenerate the adult mammalian spinal cord neurons so as to replace the embryonic motoneurons in the stretch reflex tissue engineered construct with adult motoneurons. In this body of work, the different tissue engineering strategies and technologies have been addressed to enable the recreation of a in vitro cellular prototype of the stretch reflex circuit with special emphasis on building the motoneuron to muscle segment of the circuit. In order to recreate the motoneuron to muscle segment of the stretch reflex arc, a successful methodology to tissue engineer skeletal muscle and motoneuron was essential. Hence the recreation of the motoneuron to muscle segment of the stretch reflex circuit was achieved in two parts. In the part 1 (Chapters 2-5), the challenges in skeletal muscle tissue engineering were examined. In part 2 (Chapters 6-7), apart from tissue engineering the motoneuron to muscle segment, the real time synaptic activity between motoneuron and muscle segment were studied using extensive video recordings. In part 3 (Chapters 8-10), an innovative attempt had been made to tissue engineer the adult mammalian spinal cord neurons so that in future this technology could utilized to replace the iv embryonic neurons used in the stretch reflex circuit with adult neurons. The advantage of using adult neurons is that it provides a powerful tool to study older neurons since these neurons are more prone to age related changes, neurodegenerative disorders and injuries. This study has successfully demonstrated the recreation of the motoneuron to muscle segment of the stretch reflex arc and further demonstrated the successful tissue engineering strategies to grow adult mammalian spinal cord neurons. The different cell culture technologies developed in these studies could be used as powerful tools in nerve-muscle tissue engineering, neuro-prosthetic devices and in regenerative medicine.

The neuromuscular junction (NMJ) exhibits an extraordinary capacity for adaptation and plasticity throughout an individual's lifespan. This remarkable adaptability assumes a central role in safeguarding optimal neuromuscular function and counteracting neurodegenerative processes commonly associated with aging and prevalent neuromuscular disorders. The plasticity of the NMJ is under the influence of its cellular constituents, including the ⍺-motoneuron and the innervated muscle fiber. Among the diverse array of regulatory molecules, AMP-activated protein kinase (AMPK) plays a pivotal role in governing the phenotype of these cellular components, thereby potentially contributing to synaptic modifications. To explore the regulatory role of AMPK on the NMJ phenotype, we undertook a comprehensive investigation encompassing transgenic, pharmacologic, and physiologic manipulations of this kinase. In Study 1, we investigated the significance of skeletal muscle AMPK during aging, revealing its necessity in preserving NMJ integrity. Moreover, we observed that pharmacological and physiological activation of AMPK result in an enhanced synaptic gene profile in young animals, suggesting its role in NMJ modulation. Building upon these insights, we validate the stimulatory effects of a pan-AMPK activator, MK-8722 (MK), in the context of a prevalent neuromuscular disorder, Duchenne Muscular Dystrophy (DMD). Our investigations demonstrated that MK effectively evoked AMPK activation and downstream signaling in dystrophic muscle, providing the experimental foundations our third study. Here, we assess of the chronic effects of daily MK treatment in a pre-clinical DMD model and revealed significant improvements in mitochondrial health, neuromuscular function, and a reduction in muscle fibrosis and fatigue. Taken together, these findings support a critical role of AMPK in neuromuscular plasticity and highlight the kinase as a promising therapeutic target for muscular dystrophy. / Dissertation / Doctor of Philosophy (PhD) / The neuromuscular junction (NMJ) plays a vital role in maintaining muscle function and countering aging and neuromuscular disorders. This thesis investigated the role of AMP-activated protein kinase (AMPK) in neuromuscular biology during conditions of health and disease. We conducted various experiments involving genetic modifications, drug treatments, and exercise. First, we determined that AMPK is necessary to maintain the NMJ during aging. Stimulation of AMPK with a potent activator, MK-8722 (MK), led to elevated NMJ-related gene expression. We then shifted our focus to the most prevalent neuromuscular disorder, Duchenne Muscular Dystrophy (DMD). Our results showed that MK activated AMPK in dystrophic mice, prompting us to further investigate the long-term effects of daily treatment in a pre-clinical DMD model. Repeated MK treatment significantly improved neuromuscular function and reduced the symptoms of DMD. Together, our comprehensive investigation demonstrates the critical role of AMPK in shaping neuromuscular plasticity during healthy and diseased conditions.

Bacterial vaginosis (BV), a common female reproductive tract (FRT) condition characterized by an overgrowth of anaerobic species concurrent with the disappearance of commensal Lactobacilli species, is associated with a 60% increased risk of HIV-1 transmission. However, the role of the FRT epithelia in bacterial vaginosis-associated bacteria (BVAB)-augmented HIV- 1 transmission is unclear. To evaluate the increased risk of HIV-1 acquisition, we treated FRT epithelia with Atopobium vaginae, a prevalent BVAB, to determine the nature of the host response to BVAB exposure. Treatment of endocervical cells with A. vaginae resulted in a 1500-fold increase in the expression of the antimicrobial peptide hBD-2, an inflammatory cytokine response, and delocalization of the tight junction protein ZO-1 from cell borders. Conditioned media (CM) from the coculture of FRT epithelia and A. vaginae also generated an inflammatory immune response and lowered the transepithelial electrical resistance in polarized endocervical monolayers. Changes in HIV-1 infection were measured in TZM-bl reporter cells, which contain a luciferase gene under the control of an HIV-1 long terminal repeat (LTR) region that is activated by the binding of Tat, an HIV-1 protein that drives viral replication. NFκB is a major host-derived transcription factor that regulates the expression of many genes involved in inflammation and the innate immune response. Interestingly, NFκB has been reported to bind Tat-activated response elements within the LTR of HIV-1, driving viral transcription. TZM-bl cells were treated with CM in the absence of HIV-1, which resulted in increased luciferase production that could be suppressed by the NFκB inhibitor TPCA-1. These data suggest that epithelially derived products from the coculture of FRT cells and A. vaginae enhance HIV-1 infection by causing cervical barrier dysfunction and increasing HIV replication efficiency through NFκB.

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<p> In the current research, use of p-n junction GaAs nanowires (NWs) grown by gas source molecular beam epitaxy on GaAs (111) B substrates for the fabrication of flexible solar cells are reported. The solar cells were fabricated by embedding the NWs in a polymer matrix (SU8 2), followed by ohmic contact formation to the tops of the NWs as well as the rear side of the substrate. I-V characteristic curves were obtained by illuminating the solar cells using a solar simulator, indicating a photovoltaic effect. NWs were also detached from the substrate by different methods and successfully transferred onto a flexible substrate for potential use as solar cells. Scanning electron microscopy was used throughout the research for characterization and optimization of the fabrication processes including NW embedment, removal from the substrate, and contact formation.</p> / Thesis / Master of Applied Science (MASc)

While the terms reduce, reuse, and recycle are common concepts in minimizing resource waste, most people do not think twice about energy as a resource or the large amounts of wasted energy in wastewater treatment and industrial processes. Recovery of wasted energy or reducing the net energy consumption of such processes would save resources and reduce energy costs. This research investigated emerging energy systems for handling wastewater (bioelectrochemical systems) and waste heat (ion exchange membrane systems) to elucidate and quantify thermodynamic and kinetic phenomena in biological and electrochemical reactions. Bioelectrochemical systems utilize exoelectrogenic microorganisms for wastewater treatment energy recovery in the form of electricity or biogas. The substrate utilization and electron transfer by exoelectrogens to the bioanode have not been clearly explained and thus there are no commonly accepted models for bioanode performance. A comprehensive model for bioanode operation was proposed including equilibrium, kinetics, and microbiological characteristics. The utilization and preference of different organic substrates were also assessed with electrochemical techniques and it was found that linear sweep voltammetry and exchange current are good indicators of whether a substrate is directly or indirectly utilized by exoelectrogenic microorganisms. This research also investigated ion exchange membrane systems for energy recovery from waste-grade heat, such as that wasted in the steel refinery and power industries, using concentration gradients of ammonium bicarbonate solutions. Estimation of the junction potential (amount of concentration gradient energy) has significant technical difficulties for highly concentrated ammonium bicarbonate solutions (e.g., unknowns in equilibrium speciation and activity coefficient determination). A straightforward estimation method was proposed and found to be able to reliably determine the junction potential across an ion exchange membrane based on conductivity measurement, simplifying the model for junction potential determination. / Thesis / Doctor of Philosophy (PhD)

A novel type of alternating-current (AC) powder electroluminescent (EL) device that relies on nanowire-phosphor heterogeneous junction structure has been developed. It shows promise for manufacturing of highly stable powder EL devices. To pursue this goal, manganese ion (Mn2+)-doped zinc germanate (Zn2GeO4:Mn) oxide phosphor was synthesized and used as EL powder material for the fabrication of the new types of AC powder EL devices. The Zn2GeO4:Mn oxide phosphor powder could eliminate the well-known degradation problem of zinc sulfide (ZnS)-based AC powder EL devices predominant in the current marketplace. In order to realize a high brightness at a relatively low operating voltage, a conductive semiconductor nanowire architecture using zinc oxide (ZnO) and copper oxide (CuO) nanowires with sharp-tip features, was created and integrated into conventional AC powder EL structures. Particularly, vertically-aligned n-type ZnO nanowires arrays were successfully synthesized on a Zn2GeO4:Mn polycrystalline substrate for the first time, and the growth behavior using a chemical vapor deposition (CVD) process was investigated. The density of the ZnO nanowires could be effectively controlled by some experimental parameters, such as the density of gold catalyst nanoparticles, and spatial distance between substrate and CVD source powders. This novel ZnO nanowire-decorated Zn2GeO4:Mn phosphor architecture was used to fabricate top-emission AC powder EL devices. On the other hand, a vertically-aligned ZnO nanowire array was directly synthesized on a thin film indium-tin-oxide (ITO)-coated glass substrate for fabrication of bottom-emission AC powder EL device. The nanowires were adopted to form heterogeneous junction structures between the tips of the nanowires and the Zn2GeO4:Mn EL powders, so that the composites could have a similar electrical field enhancement as in the needle-like CuxS precipitates within widely-used ZnS:Cu EL powder materials. The behavior of these top- and bottom- emission AC powder EL devices was also studied. Alternatively, vertically-aligned p-type CuO nanowires were prepared by a thermal oxidation method. Reliable heterogeneous junction structures were formed by a simple drop-coating method. The CuO nanowire-based AC powder EL device has excellent brightness maintenance with a loss of luminescent intensity under 1 % at over 10 cd/m2 luminance during 360 hours of operation. The integrating of semiconductor nanowires into conventional AC powder EL device structures offers the very promising prospect of fabrication of simple, low-cost, scaled-up EL devices that could fundamentally solve the limited operational lifetime of current ZnS-based AC powder EL devices. / Thesis / Doctor of Philosophy (PhD)