Mechanics of the urethral duct: tissue constitutive formulation and structural modeling for the investigation of lumen occlusion.

Urinary incontinence, often related to sphincter damage, is found in male patients, leading to a miserable quality of life and to huge costs for the healthcare system. The most effective surgical solution currently considered for men is the artificial urinary sphincter that exerts a pressure field on the urethra, occluding the duct. The evaluation of this device is currently based on clinical and surgical competences. The artificial sphincter design and mechanical action can be investigated by a biomechanical model of the urethra under occlusion, evaluating the interaction between tissues and prosthesis. A specific computational approach to urethral mechanics is here proposed, recalling the results of previous biomechanical experimental investigation. In this preliminary analysis, the horse urethra is considered, in the light of a significant correlation with human and in consideration of the relevant difficulty to get to human samples, which anyway represents the future advance. Histological data processing allow for the definition of a virtual and a subsequent finite element model of a urethral section. A specific hyperelastic formulation is developed to characterize the nonlinear mechanical behavior. The inverse analysis of tensile tests on urethra samples leads to the definition of preliminary constitutive parameters. The parameters are further refined by the computational analysis of inflation tests carried out on the entire urethral structure. The results obtained represent, in the light of the correlation reported, a valid preliminary support for the information to be assumed for prosthesis design, integrating surgical and biomechanical competences.