Investigation of Fiber-Driven Mechanical Behavior of Human and Porcine Bladder Tissue Tested Under Identical Conditions

Abstract

The urinary bladder is a highly dynamic organ, that undergoes large deformations several times a day. Mechanical characteristics of the tissue are crucial in determining the function, and dysfunction, of the organ. Yet, literature reporting on the mechanical properties of human bladder tissue is scarce and, at times, contradictory. In this study, we focused on mechanically testing tissue from both human and pig bladders using identical protocols, to validate the use of pigs as a model for the human bladder. Furthermore, we tested the effect on tissue mechanical properties of two treatments, elastase to digest elastin fibers and oxybutynin to reduce smooth muscle cells spasticity, as well as of the anatomical direction of testing. We also implemented two different material models to aid in the interpretation of the experimental results. We found that human tissue behaves similarly to pig tissue at high deformations (collagen-dominated behavior) while we detected differences between the species at low deformations (amorphous matrix-dominated behavior). Our results also suggest that elastin could play a role in determining the behavior of the collagen fibers network. Finally, we confirmed the anisotropy of the tissue which reached higher stresses in the transverse when compared to the longitudinal direction.

Quantifying Whole Bladder Biomechanics Using the Novel Pentaplanar Reflected Image Macroscopy System

“…Our intention in doing so was twofold: rst it allowed us to correlate our mechanical ndings to prior literature on ex vivo bladder lling and in vivo cystometry in mice (Heppner et al 2016). Second, by moving to supraphysiological pressures we could also assess the previously proposed model of collagen ber recruitment made from uniaxial stress/stretch measurements (Tuttle et al 2022;Tuttle et al 2021) and apply it to the intact bladder con guration.…”

“…The anatomical makeup of the bladder wall is clearly non-homogenous; smooth muscle cells, blood vessels, nerves, and urothelial cells exist heterogeneously throughout the bladder wall (Neuhaus and Schwalenberg 2012). Multiple studies have examined the active and passive behavior of the bladder wall using similar calculations (reviewed in (Roccabianca and Bush 2016)), and it is important to consider that regional differences in mechanical properties do occur (Tuttle et al 2021). Nonetheless, given the paucity of information as the biomechanical properties of the intact bladder wall during lling, the value of the measurements included here are not diminished and serve as a springboard for more in-depth measurements in the future.…”

A constrained mixture-micturition-growth (CMMG) model of the urinary bladder: Application to partial bladder outlet obstruction (BOO)

“…We assume an additive decomposition of the stresses arising from the passive and active components. For each layer, the passive contributions arise from collagen fibers as well as non-collagenous, isotropic component that accounts for the collective (passive) response of elastin, amorphous matrix and low stress behavior of smooth muscle cells ( Tuttle et al, 2021 ). The subscript L denotes the wall layer, L = LP , DL and AD denotes lamina propria, detrusor muscle layer and adventitial layer, respectively.…”

“…The isotropic (non-collagenous) components are modeled as a neo-Hookean material ( Tuttle et al, 2021 ), with strain energy function and corresponding Cauchy stress, where k L , nc being stiffness-like material constants, is the left Cauchy–Green deformation tensor.…”

A Data-Driven Memory-Dependent Modeling Framework for Anomalous Rheology: Application to Urinary Bladder Tissue

“…However, due to the differences in mechanical testing protocols as well as modeling, most of the results cannot be compared with one another and often results in contradicting conclusions. While several pathologies of the lower urinary tract are associated with dramatic changes of the mechanical behavior of the bladder wall [48], still much is unknown about the mechanisms that affect this organ, not just in diseased states but in healthy as well. In this study, we focus on the healthy behavior of the porcine urinary bladder, which a present work suggested is a good model for the human urinary bladder.…”