It has been well established that the fundamental behaviors of mammalian cells are influenced by the physical cues that they experience from their surrounding environment. With respect to cells in our bodies, mechanically-driven morphological and phenotypic changes to our cells have been linked to responses critical to both normal development and disease progression, including lung, heart, muscle and bone disorders, and cancer. Although significant advancements to our understanding of cell behavior have been made using 2D cell culture methods, questions regarding how physical stretch guides cell behavior in more complex 3D biological systems remain unanswered. To address these questions, we used microfabrication techniques to develop vacuum-actuated stretchers for high throughput stretching and dynamic mechanical screening of 3D microtissue cultures. This thesis contains five research chapters that have utilized these devices to advance our understanding of how cells feel stretch and how it influences their behavior in a 3D matrix. In the first research chapter (chapter 2), we characterized how stretch is transferred from the tissue-level to the single-cell level and we investigated the cytoskeletal reinforcement response to long-term mechanical conditioning. In the second research chapter (chapter 3), we examined the effects of an acute dynamic stretch and found that 3D cultures soften through actin depolymerization to homeostatically maintain a mean tension. This softening response to stretch may lengthen tissues in our body, and thus may be an important mechanism by which airway resistance and arterial blood pressure are controlled. In the third and forth research chapters (chapter 4-5), we investigated the time dependencies of microtissues cultures and we found that their behavior differed from our knowledge of the rheological behavior of cells in 2D culture. Microtissues instead followed a stretched exponential model that seemed to be set by a dynamic equilibrium between cytoskeletal assembly and disassembly rates. The difference in the behavior from cells in 2D may reflect the profound changes to the structure and distribution of the cytoskeleton that occur when cells are grown on flat surfaces vs. within a 3D environment. In the fifth and final research chapter (chapter 6), we examined how mechanical forces may contribute to the progression of tissue fibrosis through activating latent TGF-β1. Our results suggest that mechanical stretch contributes to a feed forward loop that preserves a myofibroblastic phenotype. Together these investigations further our understanding of how cells respond to mechanical stimuli within 3D environments, and thus, mark a significant contribution to the fields of mechanobiology and cell mechanics.

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Select epithelial regions of the bovine inner ear were established and maintained in cell culture. Marginal cells from the stria vascularis and dark cells from the posterior wall of the utricle were isolated, dissociated and placed in culture medium. Within 24 h, cellular islands of hexagonal-shaped, epithelial-like cells from both the stria vascularis and posterior utricular wall were readily identifiable by inverted light microscopy. Ultrastructural examination of both the cultured stria marginal cells and utricular dark cells revealed that both cell types had numerous microvilli on their apical surfaces and interdigitating infoldings of their basolateral surfaces. Apical tight junctional complexes were present between apposing cells. These findings demonstrate that inner ear bovine epithelial cells can be successfully isolated and maintained in culture, and that such cells retain certain of their in vivo morphological characteristics.

Objective Plasma fibrinogen has been defined as a risk factor of cardiovascular disease and may play a role in the development of cardiac hypertrophy. We have previously demonstrated that the Toll-like receptor 4 (TLR4)-mediated myeloid differentiation primary response protein 88 (MyD88)-dependent nuclear factor-κB (NF-κB) pathway is involved in cardiac hypertrophy. The present study aimed to investigate whether fibrinogen will stimulate the hypertrophic response of cardiac myocytes and to examine the role of the TLR4/MyD88/NF-κB pathway in fibrinogen-induced cardiac hypertrophy. Methods and Results Cardiac hypertrophy was induced by transverse aortic banding for 5 weeks in Sprague-Dawley rats. The deposition of fibrinogen in the left ventricle, as determined by immunohistochemistry and immunoblotting, was increased. Aortic banding also significantly enhanced the association of TLR4 with MyD88 and increased NF-κB activity. In-vitro studies showed that fibrinogen induced a dose-dependent, hypertrophic response of neonatal cardiomyocytes. Fibrinogen stimulation significantly increased myocyte size, 3H-leucine incorporation and mRNA levels of atrial natriuretic peptide (ANP); fibrinogen challenge also significantly increased associations of TLR4 with MyD88 and NF-κB binding activity. Transient transfection of cardiomyocytes with a dominant-negative MyD88 plasmid significantly attenuated the fibrinogen-induced hypertrophic response of neonatal cardiac myocytes and blunted fibrinogen-increased activation of the TLR4/MyD88/NF-κB signaling pathway. Conclusion Our results suggest that fibrinogen induces hypertrophic response of cardiomyocytes partially through a TLR4-mediated, MyD88-dependent NF-κB pathway.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nutrition and Food Science, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Pages 373-383 reprint from Developments in Industrial Microbiology. / Bibliography: p. 243-261. / by Robert James Fleischaker, Jr. / Ph.D.

Indiana University-Purdue University Indianapolis (IUPUI) / Hearing loss and vestibular dysfunction are inner ear disease states that arise from an array of diverse etiologies that interfere with mechanosensory hair cell function, including: congenital syndromes, noise-induced trauma, ototoxic drugs, and aging. The investigation of normal inner ear development and the pathological aberrations that cause inner ear disease has been previously advanced through formation of an easily generated, scalable, accurate in vitro model system that readily facilitates experimental applications. This model utilizes a 3D floating cell culture protocol which guides differentiation of stem cell aggregates into inner ear organoids, which are vesicles containing a sensory epithelium with functioning mechanosensory hair cells. Inner ear organoid formation enables studying the effects of modulating the signaling pathways that guide developing inner ear structure and function. The Notch signaling pathway heavily influences the formation of the inner ear through two major mechanisms: lateral induction of sensory progenitor cells and lateral inhibition to determine which of those progenitors differentiate into mechanosensory hair cells. The effects of inhibiting Notch signaling within the inner ear organoid system were explored through application of the ɣ-secretase inhibitor MDL28170 (MDL) at a concentration of 25μM on day 8 of organoid culture. Aggregates were harvested on day 32, fixed, sectioned, and stained according to a standard immunohistochemistry protocol. Sections were stained for the mechanosensory hair cell markers Myosin7a (Myo7a) and Sox2. MDL-treated aggregates demonstrated statistically significant reductions in the total number of vesicles and the number of vesicles containing hair cells compared to control aggregates. In contrast to control aggregates which demonstrated two distinct organoid variants (protruding and embedded), MDL-treated aggregates only formed the embedded variant. Differences in the expression pattern of Sox2, which is also a marker of stemness and neural progenitor cells were also noted between the two conditions. MDL-treated aggregates demonstrated regions of ‘ectopic’ Sox2 expression whereas Sox2 expression in control aggregates was consistently expressed within Myo7a+ regions.

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This dissertation presents studies electrodeposited MoS2 and metal-doped MoS2 thin films, and their performance for energy storage, catalysis, and biosensor applications. Ni-doped MoS2 thin films were fabricated by electrodeposition from electrolytes containing both MoS42- and varying concentrations of Ni2+, followed by annealing at 400 ºC for 2 h in an Ar atmosphere. The film resistivity increased from 11.3 µΩ-cm for un-doped MoS2 to 32.8 µΩ-cm for Ni-doped MoS2 containing 9 atom% Ni. For all Ni dopant levels studied, only the x-ray diffraction (XRD) pattern expected for MoS2 is observed, with the average grain size increases with increasing Ni content. Ni-doped MoS2 thin films were tested for their activity towards the hydrogen evolution reaction (HER) in 0.5M H2SO4. Tafel equation fits reveal that the catalytic activity for HER, as measured by the exchange current density, increases up to 6 atom% Ni, and then decreases slightly for 9 atom% Ni. Ni-doped MoS2 thin films were also tested in 1.0 M Na2SO4 for use within electrochemical supercapacitors, and the capacitance per unit area increases by 2-3x for 9 atom% Ni-doped MoS2 relative to un-doped MoS2. The highest specific capacitance obtained for Ni-doped MoS2 during galvanostatic charge-discharge measurements is ~300 F/g

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