## 3 Results
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Tissue** & \(E\) [MPa] & **UTS [MPa]** & **Failure Strain [\%]** \\ \hline Bladder & 1.40 (1.16, 1.58) & 0.47 (0.44, 0.54) & 51.42 (47.23, 54.69) \\ Buck’s fascia & 3.86 (2.18, 7.46) & 0.86 (0.66, 1.79) & 47.79 (42.45, 50.73) \\ Prostate—L & 1.54 (1.13, 2.35) & 0.44 (0.26, 0.48) & 25.37 (22.62, 45.38) \\ Prostate—T & 0.66 (0.63, 0.86) & 0.32 (0.29, 0.41) & 85.45 (77.80, 124.19) \\ Tunica albugine—L & 12.77 (10.36, 17.70) & 2.12 (1.39, 3.81) & 21.14 (17.91, 26.97) \\ Tunica albugine—T & 40.44 (35.91, 44.97) & 6.50 (3.64, 9.36) & 24.27 (16.78, 31.75) \\ \hline \hline \end{tabular} \(\mathrm{L}=\mathrm{longitudinal},\mathrm{T}=\mathrm{transversal}.\)  
\end{table} 
Table 4: For each tissue tensioned up to failure, median values (25 th, 75 th percentiles) of the elastic modulus, UTS and strain at UTS are reported. Figure 2: Stress–strain curves up to breakage resulted for all the tissues that were subjected to failure tests. Median curves are reported with 50% probability scatter bands. the minimization of the number of the parameters and the adequate interpretation of the trend of the experimental data and agrees with previous studies on LUT tissues [8,9]. The quantity \(\gamma_{1}+\gamma_{2}\) accounts for the amount of stress relaxation of the normalized curves (in percentage it represents the degree of relaxation for each tissue). The resulting normalized median stress-time curves and the related 50% probability scatter bands are shown in Figure 3, while fitting parameters are reported in Table 5.  
For the bulbar urethra (Figure 3a), differences in terms of relaxation degree were not found between distal (D) and proximal (P) regions along both the longitudinal (D 78.19%, [74.23, 82.94]%; P 78.12%, [67.24, 82.65]%) and the transversal (D 83.95%, [82.06, 86.26]%; P 80.68%, [76.14, 83.04]%) directions. Similarly, no differences resulted for the penile urethra (Figure 3b) between the D and P regions along the two tested directions. Figure 3: Relative stress–relaxation curves resulted for (**a**) bulbar and (**b**) penile urethra in distal and proximal regions, for all urethral samples tested along the (**c**) longitudinal and (**d**) transversal directions, and for (**e**) all tissues underwent stress–relaxation test. (**f**) Stress–strain curves obtained at equilibrium for bladder, tunica albuginea and urethra samples. Median curves are reported together with 50% probability scatter bands. For these reasons, median values of the resulting parameters \(\gamma_{1}\), \(\gamma_{2}\), \(\tau_{1}\) and \(\tau_{2}\) are reported in Table 5 without distinguishing the distal and proximal regions. Both the bulbar and penile urethral samples suggested different relaxation phases if tested along the longitudinal or the transversal direction. In particular, the penile urethra showed a stress decrease equal to 87.59% [83.31, 90.10]% along the transversal direction, while equal to 79.33% [75.63, 84.03]% along the longitudinal one. Analyzing all the urethral samples tested longitudinally, the relaxation curves resulted independent of the harvesting region, as shown in Figure 3. On the other hand, considering all the urethral samples tested transversally (Figure 3), different urethral regions determined different degrees of relaxation, reporting the maximum value for the penile urethra (87.59%, [83.31, 90.10]%) and the minimum for the bulbar urethra (83.22%, [79.84, 86.02]%). All these curves obtained from urethral samples resulted in an intermediate region between those relating to the tunica albuginea tested along the transversal direction and those related to the bladder (Figure 3) exhibited a final drop of normalized stress equal to 65.74% [53.47, 82.12]% and 88.55% [84.00, 91.18]%, respectively. Moreover, original stress-time data were processed to analyze the tissue mechanical response at the end of relaxation phases, when all the time-dependent phenomena completely occurred.