Functional Grading of a Transversely Isotropic Hyperelastic Model with Applications in Modeling Tricuspid and Mitral Valve Transition Regions.

Rajarshi Roy,Joseph P R O Orgel,Yaoyao Xu,Kevin Lister,Caleb Yow,Eric Warren,Rama S Madhurapantula

doi:10.3390/ijms21186503

Abstract

Surgical simulators and injury-prediction human models require a combination of representative tissue geometry and accurate tissue material properties to predict realistic tool–tissue interaction forces and injury mechanisms, respectively. While biological tissues have been individually characterized, the transition regions between tissues have received limited research attention, potentially resulting in inaccuracies within simulations. In this work, an approach to characterize the transition regions in transversely isotropic (TI) soft tissues using functionally graded material (FGM) modeling is presented. The effect of nonlinearities and multi-regime nature of the TI model on the functional grading process is discussed. The proposed approach has been implemented to characterize the transition regions in the leaflet (LL), chordae tendinae (CT) and the papillary muscle (PM) of porcine tricuspid valve (TV) and mitral valve (MV). The FGM model is informed using high resolution morphological measurements of the collagen fiber orientation and tissue composition in the transition regions, and deformation characteristics predicted by the FGM model are numerically validated to experimental data using X-ray diffraction imaging. The results indicate feasibility of using the FGM approach in modeling soft-tissue transitions and has implications in improving physical representation of tissue deformation throughout the body using a scalable version of the proposed approach.

Highlights

The simulated fiber stretch is larger in regions closer to the LL than the chordae tendinae (CT), which is a consequence of greater compliance in the “pure” LL tissue compared to “pure” CT tissue, and this is reflected in the functionally graded material (FGM) model
Certain outliers can be observed in the X-Ray diffraction (XRD) orientations at 15% stretch which are near-orthogonal to the simulated orientations—these are most likely attributed to XRD signals from secondary fibers in the transition region [44]
These results indicate an asymmetric distribution of transversely isotropic (TI) properties at the CT–papillary muscle (PM) transition for both tricuspid valve (TV) and mitral valve (MV) specimens, which is consistent with the experimental observation of a steep increase in collagen content near the CT in our previous work [44]

Summary

Introduction

Several whole-body finite element (FE) models [2,3] have been used to supplement post-mortem human subject impact data from mechanical insults such as blunt, penetrating and blast events to advance the fields of crashworthiness and impact biomechanics research. Both surgical simulators and whole-body injury-prediction models require detailed geometrical and biomechanical characterization of soft tissue to predict accurate tool-tissue interaction forces and damage propagation in the human body respectively. The vast body of literature on soft-tissue characterization focus on organ-specific homogeneous tissue properties [1,3], with lesser emphasis on the transition regions between various tissue types

Methods

Results

Discussion

Conclusion