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

Abstract

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.

Biomechanical analysis of the interaction phenomena between artificial urinary sphincter and urethral duct

“…Finally, aiming to ensure the reliability of the developed model of the urethra, the model was exploited to simulate inflation tests. The agreement between model and experimental results suggested the quality of the model, as fully reported in …”

“…The specific characterization of human urethra is in progress by additional experimental activities on human samples, facing a relevant difficulty in acquisition, management and limited number of samples . Similarly, conformations, mechanics, and performances of AUS cuff have been evaluated by coupling experimental and computational methods, aiming to elucidate strengths and weaknesses of current devices . The accurate analysis of the constitutive materials and of the geometrical characteristics of AUS cuff is justified in the light of the complex behavior that the cuff assumes during occlusive function.…”

“…A computational framework of urethra mechanics is based on experimental investigations of the mechanical properties of urethral tissues and structures developed by the authors and reported in detail in previous works . Horse urethra samples were cut in transversal direction after a histological fixation process .…”

“…The constitutive parameter K v is related to bulk stiffness, as B = 2 K v , C 1 is related to tissue shear stiffness in the unstrained configuration, as G = 2 C 1 , while the nonlinearity parameter α 1 specifies tissue stiffening with stretch. The inverse analysis of data form tensile tests on urethra samples enabled to evaluate constitutive parameters, as described in …”

“…The biomechanical analysis of urethral tissues and structures was previously investigated using an integrated experimental and computational approach. [10][11][12][13][14] Based on tensile and inflation tests on urethra samples, a specific hyperelastic formulation was defined to characterize the non-linear mechanical behavior of urethral tissues, while the inverse analysis of experimental data enabled to identify constitutive parameters. Histological data of urethral duct were collected, leading to the definition of virtual solid and finite element models.…”