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Title
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Correlating Microstructural Properties to Macroscopic Shear Mechanics to Improve the Understanding of Tissue Biomechanics
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Creator
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Cahoon, Stacey Marie
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Date
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2023
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Description
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Understanding tissue biomechanics is of interest for modeling organ injury from external loads, development of tissue surrogate materials, and...
Show moreUnderstanding tissue biomechanics is of interest for modeling organ injury from external loads, development of tissue surrogate materials, and creating new biomarkers for disease. Probing the response of soft tissue in shear can provide information on histopathology, provided a methodology exists that connects the macroscopic mechanical properties with cell-level properties. Two of the available methods to measure the macroscopic shear viscoelastic properties of soft tissue are oscillatory shear rheometry and ultrasound shear wave elastography (SWE). Due to its accuracy, rheometry is the gold standard, but it is destructive, requires excised homogeneous samples, and can only be applied ex-vivo. SWE is an emerging non-invasive imaging technique which requires validation, ostensibly by comparing with rheometry. Histology is the gold standard for providing morphological information on the cell level, which can determine tissue pathology. The challenge is to connect the macroscopic mechanical metrics derived from SWE and rheometry to the tissue microstructure. To address this challenge, mathematical models can be used that employ multiple, judiciously chosen measurements of macroscopic shear properties and histology to estimate intrinsic mechanical properties at the cell level.A class of homogeneous and composite lipid phantoms mimicking the mechanical properties of brain white matter were fabricated to test a novel stereotactic system and an optimized SWE imaging protocol. The shear stiffness measurements obtained with SWE on the whole phantom were validated with rheometry performed on a series of samples made with the same material as the phantoms. The same procedure was applied to porcine brain white matter excised from fresh whole brains (n=3). Cylindrical cores were extracted from the corpus callosum area, sliced into discs and microscopic sections were subsequently removed for histology. Good agreement was found between the SWE and rheometry measurements of shear stiffness, which generally increases with the level of compressive prestress. Immunofluorescence was used to stain separately the axon neurofilaments and myelin sheaths, and digital image analysis of the confocal microscopy images allowed the estimation of axon volume fraction and axon-to-myelin ratio in the corpus callosum. Using these metrics and a composite mechanical model, a connection between the macroscopic shear measurements and the viscoelastic properties of axon and glia matrix was made for porcine brain tissue. Similarly, rheometry was used to measure the macroscopic properties of decellularized porcine myocardium extracellular matrix (ECM) in two different fiber locations, and for three different fiber orientations. The mechanical properties were found to be dependent upon fiber location, but not on fiber orientation. Since collagen is a primary supportive structure for the ECM, several microscopic slices were probed with immunofluorescence to compute the collagen I and collagen IV volume fractions. Another mechanical model was employed to establish a connection between the macroscopic properties and the mechanical properties of the collagen matrix in decellularized porcine myocardial ECM.This dissertation highlights the use and integration of three different experimental techniques (rheometry, ultrasound SWE, and histology) to correlate key microstructural properties of soft, fibrous tissues (ex-vivo healthy porcine brain white matter and myocardium ECM) with macroscopic shear mechanics. The consideration of the effect of compressive prestress is noteworthy. The reported baseline data for the tissues under shear loading and prestress are pertinent to the physiological function of these tissues, and therefore constitute preliminary data and a necessary first step before a systematic study of the biomechanics of the same tissues in vivo is performed.
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Title
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An Iterative Method Converging to a Positive Solution of Certain Systems of Polynomial Equations
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Date
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2011, 2011
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Description
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We present a numerical algorithm for finding real non-negative solutions to a certain class of polynomial...
Show moreWe present a numerical algorithm for finding real non-negative solutions to a certain class of polynomial
equations. Our methods are based on the expectation maximization and iterative proportional fitting algorithms,
which are used in statistics to find maximum likelihood parameters for certain classes of statistical models.
Since our algorithm works by iteratively improving an approximate solution, we find approximate solutions in the
cases when there are no exact solutions, such as overconstrained systems.
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Collection
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Journal of Algebraic Statistics
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Title
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Adaptive Building Skin
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Creator
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Kim, Minjae
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Date
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2010-05-01, 2010-05-01
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Description
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City is made up of diversity and density. Diverse factors make activities and different relationships in a city. These are very sensitive to...
Show moreCity is made up of diversity and density. Diverse factors make activities and different relationships in a city. These are very sensitive to other factors’ changes. Their various responses make city dynamic and finally characterize the face of a city or a town. Buildings are one of dynamic factors in a city. The building facade which determines building’s identity marks the transition between outside and inside. The facade has a strong relationship between building programs and urban activities. Their looks make a huge effect on urban environment. But buildings’ configuration is fixed once design choices are made. Buildings are conceived as a rigid objects and inflexible, unresponsive, and unsustainable. Considering that buildings are the largest contributor to the city environment, building should be responsive to changes and facade performance should be more active to building programs. Adaptive building facade will be the means that can address these challenges.
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Title
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Supplemental Figures and Data _ Process Design for Small-Scale Production of PEGDA-NVP Hydrogel Nanoparticle
Emulsions for Therapeutic Applications
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Date
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2025
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Description
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This data set supports the process development work described in the associated manuscript, capturing the...
Show moreThis data set supports the process development work described in the associated manuscript, capturing the
transition from bench-scale synthesis to small-scale process development of hydrogel nanoparticles. It includes
the raw and processed quantitative data for experimental variables tested during this scale-down effort.
Additionally, the data set provides the original red-green channel versions of fluorescence microscopy images
used in cell studies. In the manuscript, these images were adjusted to be accessible for readers with red-green
color vision deficiency; here, the unmodified channel versions are made available to ensure scientific
transparency and reproducibility.
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