Mechanical behaviour of the porcine urinary bladder — A first comparative analysis of material properties at different length scales

This study examines the passive mechanical behaviour of the porcine urinary bladder at various length scales. Biaxial tensile tests on square urinary bladder wall specimens are compared with whole urinary bladder inflation experiments. Both measurements are compared using finite element analysis to propagate layer properties across the entire organ, and local strain measurements are taken during inflation experiments to create comparable testing conditions to those of the biaxial tests. Biaxial tension tests at tissue level (n=6) and whole bladder tests (n=6) yielded an average Cauchy stress of 12.9 ± 4.1 kPa and 13.4 ± 1.7 kPa, respectively, for a stretch of λ=1.7 representing the maximum stretch during inflation. In addition, the properties of the bladder wall's different layers were investigated to gain insight into its individual components. The variability observed in the experimental results was incorporated into the analysis using a material model and Bayesian inference. The resulting range of material parameters formed the basis for simulations, allowing for further interpretation due to the simplicity of the material model. This study links tissue-level measurements to the entire organ, as well as layer properties to the entire urinary bladder wall.