Constitutive formulations for the mechanical investigation of colonic tissues

Abstract

A constitutive framework is provided for the characterization of the mechanical behavior of colonic tissues, as a fundamental tool for the development of numerical models of the colonic structures. The constitutive analysis is performed by a multidisciplinary approach that requires the cooperation between experimental and computational competences. The preliminary investigation pertains to the review of the tissues histology. The complex structural configuration of the tissues and the specific distributions of fibrous elements entail the nonlinear mechanical behavior and the anisotropic response. The identification of the mechanical properties requires to perform mechanical tests according to different loading situations, as different loading directions. Because of the typical functionality of colon structures, the tissues mechanics is investigated by tensile tests, which are performed on taenia coli and haustra specimens from fresh pig colons. Accounting for the histological investigation and the results from the mechanical tests, a specific hyperelastic framework is provided within the theory of fiber-reinforced composite materials. Preliminary analytical formulations are defined to identify the constitutive parameters by the inverse analysis of the experimental tests. Finite element models of the specimens are developed accounting for the actual configuration of the colon structures to verify the quality of the results. The good agreement between experimental and numerical model results suggests the reliability of the constitutive formulations and parameters. Finally, the developed constitutive analysis makes it possible to identify the mechanical behavior and properties of the different colonic tissues.

Alterations in biomechanical properties and microstructure of colon wall in early-stage experimental colitis

“…The colon wall is subject to tensile loading and finite strains, and in general, presents a nonlinear and anisotropic mechanical response (8,10,13). This is primarily owing to collagen fiber distribution within the microstructure of its subcomponents (14). Notably, the mechanical properties of biological soft tissue may be altered significantly in response to pathological changes (15).…”

Computational analysis of mechanical stress in colonic diverticulosis

“…In our previous study of swine tissue behavior, we established an anisotropic material constitutive model for the descending and spiral regions of the swine colon based on simultaneous inflation and extension tests 15 . This model has been shown in several previous studies to capture adequately the anisotropic behavior of the colon 19,[34][35][36] . The material parameters established in our previous study were retained since, to our knowledge, it is the only study modeling a large animal colon under inflation and extension, the two major deformation modes of the colon.…”

“…Most are, however, based on isotropic material models [16][17][18] despite the anisotropic nature of the colon tissue. One study implemented an anisotropic computational model based on uniaxial testing 19 . To our knowledge, this is the first anisotropic computational model of the colon based on simultaneous inflation and extension data.…”

Modelling and quality control of robot-assisted gastrointestinal assembly

“…Although the gastrointestinal tract is a complex multilayer structure. The intestinal wall is simplistically modelled as one layer material due to the lack of appropriate data identified for separate layers [7,10]. With this mechanical model, the gastrointestinal anastomosis quality can be related to certain controllable design parameters including the leg chamfer, the shape of the anvil, the contact friction among staple, anvil and tissue, and the shooting speed.…”