Most organs in the human body have a unique mechanical function, which depends on the pressures and forces exerted onto the organ, as well as its comprising tissues' composition and mechanical behavior. However, pathological conditions can cause inflammation, over-pressurization, or over-distension, resulting in remodeling of the tissues' constituents, such as cell hypertrophy or fibrosis, which in turn alters the mechanical behavior of the tissue and, ultimately, whole organ function. For this reason, it is crucial to understand the mechanical behavior of both healthy and pathologically remodeled biological tissues. The focus of this dissertation will be on developing constituent-specific, descriptive constitutive models for the left ventricle and urinary bladder under healthy and pathological conditions.Many constitutive models have been proposed for soft tissues, including the left ventricle and the urinary bladder. These models include descriptions of the mechanical behavior of these tissues with regard to characteristics such as general non-linear behavior, fiber orientation and dispersion, and viscoelastic behavior, for both healthy and pathological conditions. Techniques for developing and validating these models typically include fitting the models' parameters to experimental data. The following chapters will focus on uniaxial data as well as opening angle tests, and an isotropic, exponential constitutive model. Additionally, a novel model for the left ventricle is introduced that includes a term that quantifies inter-constituent mechanical interaction.Furthermore, this work aims to quantify the changes in soft tissues associated with pathology. As disease progresses in the left ventricle and urinary bladder, tissue remodeling can cause significant changes to the mechanical behavior, such as stiffening or softening of the organ walls--which can further progress disease, creating a positive feedback loop. In the left ventricle, hypertension has been studied in regard to mechanical behavior and composition of the tissue as well as residual stress (via opening angle tests). However, no current studies have shown how these changes affected the constituents' individual mechanical behaviors and stress-states. In the urinary bladder, while some studies have focused on mechanical behavior of the remodeled type I diabetic bladder, no studies have reported whether these changes are consistent with type II diabetes. The pathologies of interest in the following chapters are: hypertension in the left ventricle, type II diabetes in the urinary bladder, and radiation cystitis in the urinary bladder (as this pathology has not been previously studied for its effect on bladder wall mechanical behavior).The goals of this dissertation are to: (1) establish the need for a left ventricle constitutive model that includes a term for a mechanical inter-constituent interaction, (2) characterize the changes to the residual stress distribution of the isolated constituents in a hypertensive model of the left ventricle, (3) determine the effect of type II diabetes--both with and without the presence of obesity--on urinary bladder mechanical behavior, and (4) measure mechanical parameters and stiffness alterations to urinary bladder tissue that has undergone radiation treatment.
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