Experimental investigation of the biomechanics of urethral tissues and structures

Abstract

New Findings r What is the central question of this study?Prostheses for treatment of urinary incontinence elicit complications associated with an inadequate mechanical action. This investigation aimed to define a procedure addressed to urethral mechanical characterization. Experimental tests are the basis for constitutive formulation, with a view to numerical modelling for investigation of the interaction between the tissues and a prosthesis. r What is the main finding and its importance?Horse urethra, selected for its histomorphometric similarity to human urethra, was characterized by integrated histological analysis and mechanical tests on the biological tissue and structure, leading to constitutive formulation. A non-linear, anisotropic and time-dependent response was found, representing a valid basis for development of a numerical model to interpret the functional behaviour of the urethra.Urinary dysfunction can lead to incontinence, with an impact on the quality of life. Severe dysfunction can be overcome surgically by the use of an artificial urinary sphincter. Nonetheless, several complications may result from inappropriate functioning of the prosthesis, in many instances resulting from an unsuitable mechanical action of the device on the urethral tissues. Computational models allow investigation of the mechanical interaction between biological tissues and biomedical devices, representing a potential support for surgical practice and prosthesis design. The development of such computational tools requires experimental data on the mechanics of biological tissues and structures, which are rarely reported in the literature. The aim of this study was to provide a procedure for the mechanical characterization of urethral tissues and structures. The experimental protocol included the morphometric and histological analysis of urethral tissues, the mechanical characterization of the response of tissues to tensile and stress-relaxation tests and evaluation of the behaviour of urethral structures by inflation tests. Results from the preliminary experiments were processed, adopting specific model formulations, and also providing the definition of parameters that characterize the elastic and A. N. Natali and others viscous behaviour of the tissues. Different experimental protocols, leading to a comprehensive set of experimental data, allow for a reciprocal assessment of reliability of the investigation approach.

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

“…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 .…”

“…Masson trichrome staining was used to identify tissue morphological properties, amount of collagen and muscular fibers, and preferred orientation. Histological analyses showed strong similarity between horse distal urethra and human anterior urethra and, consequently, horse urethra samples were adopted for mechanical investigation . Mechanical uni‐axial tensile tests on urethral tissues were performed on specimens from both distal and proximal urethra, along longitudinal and circumferential directions.…”

“…A planar system of Bose ElectroForce (Bose Corporation, ElectroForce Systems Group, Eden Prairie, Minnesota) was used to perform uniaxial tensile tests. Each specimen was stretched up to a 60% strain according to a 60%/s constant strain rate . Finally, aiming to analyses the structural behavior, inflation tests were carried out on urethral tubular segments pertaining to both distal and proximal regions.…”

“…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 …”

Interaction phenomena between a cuff of an artificial urinary sphincter and a urethral phantom

“…The experimental procedure was performed for the AUS cuff without urethral phantom and then for the AUS cuff with different urethral phantoms, the latter to interpret the mechanical behavior of healthy and degraded urethrae. Urethral phantoms were developed considering different dimensions and different foams, aiming to mimic the urethra mechanics and morphometry in healthy and degraded conditions, as reported in other studies . Additional experimentations were developed to evaluate the influence of cuff size adopting a urethral phantom with a greater diameter, that is, 13 mm of diameter.…”