Type of Document Dissertation Author Gloeckner, Dorothy Claire Author's Email Address dcgst11@pitt.edu URN etd-04142003-092041 Title Tissue Biomechanics of the Urinary Bladder Wall Degree Doctor of Philosophy Program Bioengineering School School of Engineering Advisory Committee
Advisor Name Title Michael S. Sacks Committee Chair George D. Stetten Committee Member Michael B. Chancellor Committee Member Sanjeev G. Shroff Committee Member William C de Groat Committee Member Keywords
- anisotropy
- quasi-linear viscoelasticity
- spinal cord injury
- constitutive modeling
- biaxial testing
Date of Defense 2003-01-22 Availability unrestricted Abstract The urinary bladder stores urine and permits proper micturition, both functions that are inherently mechanical. Bladder research to date has been limited to whole-organ testing and simple uniaxial study, both of which are inadequate for comprehensive modeling and rigorous analysis of the mechanical properties of the bladder wall. In this work, we studied the quasi-static and time-dependent properties of the bladder wall to further understand bladder function. To obtain the requisite multiaxial data we utilized biaxial testing techniques, which allow for a more realistic physiological loading state. The goal of the study was to develop a comprehensive understanding of bladder wall biomechanics to provide insight into tissue-level bladder function. This information can be compared against other ongoing and future studies of pathologies to aid in the design of clinical treatments.The results indicated that bladder tissue 10 days after spinal cord injury was more compliant than normal bladder when referenced to the preconditioned state. However, the preconditioned state itself was different between normal and spinal-cord-injured groups, indicating large rapid changes in structure. There was a fundamental change in material behavior after spinal cord injury that indicates structural rearrangement on a microstructural fiber level. Unlike other soft tissues, there was no difference in mechanical response over three orders of magnitude of loading strain rate, most likely due to the large range of bladder function, including fast emptying and very slow filling. The time-dependent stress relaxation tests indicated that bladder behavior was dependent on stress level, with less relaxation occurring at higher stress levels. This may be because the massive structural rearrangements during normal function cause more collagen to bear load at higher stress levels as protection from over distention.
This study provided the first mechanically rigorous information regarding the tissue properties of the normal bladder wall, including comparisons to a diseased state. This information can be used to understand how differences in structure caused by disease alter the tissue behavior, and hence the biological function, of the urinary bladder.
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