Analysis of the structural behaviour of colonic segments by inflation tests: Experimental activity and physio-mechanical model

Abstract

A coupled experimental and computational approach is provided for the identification of the structural behaviour of gastrointestinal regions, accounting for both elastic and visco-elastic properties. The developed procedure is applied to characterize the mechanics of gastrointestinal samples from pig colons. Experimental data about the structural behaviour of colonic segments are provided by inflation tests. Different inflation processes are performed according to progressively increasing top pressure conditions. Each inflation test consists of an air in-flow, according to an almost constant increasing pressure rate, such as 3.5 mmHg/s, up to a prescribed top pressure, which is held constant for about 300 s to allow the development of creep phenomena. Different tests are interspersed by 600 s of rest to allow the recovery of the tissues' mechanical condition. Data from structural tests are post-processed by a physio-mechanical model in order to identify the mechanical parameters that interpret both the non-linear elastic behaviour of the sample, as the instantaneous pressure-stretch trend, and the time-dependent response, as the stretch increase during the creep processes. The parameters are identified by minimizing the discrepancy between experimental and model results. Different sets of parameters are evaluated for different specimens from different pigs. A statistical analysis is performed to evaluate the distribution of the parameters and to assess the reliability of the experimental and computational activities.

Biomechanical Constitutive Modeling of the Gastrointestinal Tissues: Where Are We?

“…They used small intestinal inflation data aimed at studying stress relaxation [98] and demonstrated that their model was able to reproduce the experimental data with a neo-Hookean formulation for Ψ E and Ψ OE in conjunction with either linear or non-linear viscous models (it was not specified which performed better). They used colonic inflation data aimed at studying creep [99] and demonstrated that their model was able to reproduce the experimental data with a Humphrey model (we classified as Fung-type) for Ψ E and Ψ OE along with a linear viscous model. They used rectal inflation data aimed at studying the behavior of the rectum under normal conditions and Hirschsprung's disease [100], and demonstrated that their model was able to reproduce the experimental data for healthy and diseased tissue with a neo-Hookean formulation for Ψ E and Ψ OE along with a linear viscous model.…”

Biomechanics of Hollow Organs: Experimental Testing and Computational Modeling

“…In the case of hollow organs, general experimental activities pertain to the mechanical and structural characterization of the specific anatomical district: mechanical tests at the tissues level [31][32][33][34], such as tensile, compression, and shear tests for the investigation of nonlinear elasticity and damage phenomena; stress relaxation and creep tests for the identification of the viscoelastic behavior; mechanical tests at the sub-structural level, such as membrane indentation tests for the evaluation of in-plane bending behavior, and opening angle tests for the identification of residual stresses [35][36][37]; mechanical tests at the structural level, such as inflation tests, for the evaluation of the pressure-volume response, and flow tests for the identification of fluid-dynamic quantities and fluid-structure interaction phenomena [38][39][40][41]. Aiming to evaluate the effects of diagnostic and surgical procedures, specific experimentations can be performed.…”