Experimental investigation of the structural behavior of equine urethra

Background and objective An integrated experimental and computational investigation was developed aiming to provide a methodology for characterizing the structural response of the urethral duct. The investigation provides information that are suitable for the actual comprehension of lower urinary tract mechanical functionality and the optimal design of prosthetic devices. Methods Experimental activity entailed the execution of inflation tests performed on segments of horse penile urethras from both proximal and distal regions. Inflation tests were developed imposing different volumes. Each test was performed according to a two-step procedure. The tubular segment was inflated almost instantaneously during the first step, while volume was held constant for about 300 s to allow the development of relaxation processes during the second step. Tests performed on the same specimen were interspersed by 600 s of rest to allow the recovery of the specimen mechanical condition. Results from experimental activities were statistically analyzed and processed by means of a specific mechanical model. Such computational model was developed with the purpose of interpreting the general pressure-volume-time response of biologic tubular structures. The model includes parameters that interpret the elastic and viscous behavior of hollow structures, directly correlated with the results from the experimental activities. Results Post-processing of experimental data provided information about the non-linear elastic and time-dependent behavior of the urethral duct. In detail, statistically representative pressure-volume and pressure relaxation curves were identified, and summarized by structural parameters. Considering elastic properties, initial stiffness ranged between 0.677 ± 0.026 kPa and 0.262 ± 0.006 kPa moving from proximal to distal region of penile urethra. Viscous parameters showed typical values of soft biological tissues, as τ1 = 0.153 ± 0.018 s, τ2 = 17.458 ± 1.644 s and τ1 = 0.201 ± 0.085, τ2 = 8.514 ± 1.379 s for proximal and distal regions respectively. Discussion A general procedure for the mechanical characterization of the urethral duct has been provided. The proposed methodology allows identifying mechanical parameters that properly express the mechanical behavior of the biological tube. The approach is especially suitable for evaluating the influence of degenerative phenomena on the lower urinary tract mechanical functionality. The information are mandatory for the optimal design of potential surgical procedures and devices.