The urinary bladder stores and voids urine through relaxation and contraction. The ability of the bladder to drastically increase in size while maintaining minimal pressure is key to proper organ function, making the study of bladder tissue mechanical characteristics crucial. Several diseases and disabilities that lead to bladder dysfunction are accompanied by pathological remodeling of the bladder wall that can dramatically impact its mechanical behavior. Before we can understand pathological changes, we must understand the healthy characteristics of the bladder. To this end, we must identify the relevancy of different animals as models of human bladder mechanics.Several studies exist that characterize either the human bladder or pig bladder. However, differences in mechanical testing protocols between studies leads to high variation in observed mechanical properties within the same species. This makes it difficult to infer the utility of the pig bladder as an effective model for human bladder mechanics. The first goal of this dissertation is to directly compare the mechanics of the human and pig bladder tested under identical conditions. To do this we have employed constitutive modeling of uniaxial tensile data from human and pig bladder specimens, and shown anisotropic behavior and comparable mechanical behavior between pig and human bladders. The second goal of this dissertation is to assess the viscoelastic properties of the porcine bladder wall, and how they are affected by anatomical location and osmotic swelling. In certain pathological conditions degradation of the urothelium can expose the bladder wall to osmotic challenge from urine, changing the hydration level, and consequently, viscoelastic behavior of the tissue. Through osmotic swelling of pig bladder tissue, stress-relaxation testing, and viscoelastic constitutive modeling we have shown that high levels of urine osmolarity may lead to increased relaxation times that could increase the stress state of the bladder wall and be a driving factor in pathological remodeling. The final goal of this dissertation is to identify how a pathological condition, i.e., spinal cord injury, can affect bladder extracellular matrix morphology and compliance in the long-term. Prior studies on rat bladder mechanics after spinal cord injury have shown increased capacity and compliance of the bladder post-injury in the short-term. Through imaging, histological analysis, mechanical testing, and constitutive modeling of the long-term spinal cord injured rat bladder extracellular matrix, we have shown profound remodeling of collagen in the bladder wall after spinal cord injury, leading to an increase in capacity, and compliance. It is likely that increase in compliance is a result of the increase in fiber waviness that is seen in our histological analysis, which was predicted by our structural fiber-recruitment constitutive model.
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