# Predicting Early-Stage Damage in Pelvic Soft Tissues
Using Hyper-Viscoelastic Modeling

A. S. Caro-Bretelle, Sarah Iaquinta

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To cite this version:

A. S. Caro-Bretelle, Sarah Iaquinta. Predicting Early-Stage Damage in Pelvic Soft Tissues Using Hyper-Viscoelastic Modeling. SIMBIO-M 2024 - 7th Conference on Simulation in Biosciences and Multiphysics, Sep 2024, Hull, United Kingdom. hal-04933579

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Submitted on 6 Feb 2025

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Distributed under a Creative Commons Attribution 4.0 International License
Proceedings
SimBio-M 2024

Simulation in Biosciences

-Multiphysics

-Mechanics

-Materials

-Medicine

-Manufacturing

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Proceedings SimBio-M 2024

© 2024 The Authors, published by the University of Hull

Cottingham Road,

Kingston upon Hull

HU6 7RX, UK

https://www.hull.ac.uk/

ISBN - 978-1-906422-44-8

Proceedings of SimBio-M 2024 an online conference. The information contained in this volume is meant to provide helpful information and ideas on the subjects discussed. Any opinions expressed are not the corporate view of the Universities involved, but these of the authors. This work is licensed under Creative Commons Attribution 4.0 International. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/. Proper reference to the articles and authors of the research papers must be made in all instances and by using the book title and ISBN number.

## Committee members

- Prof Christophe Bastien

- Prof Peter Zioupos

- Dr.-Ing. EMBA Kambiz Kayvantash

- Prof Michel Behr

- Prof Morgane Evin

- (Transport Safety and Simulations, Coventry Univ)

- (Biomedical Engineering, Univ of Hull)

- (Director of AI/ML Applications for Design and Engineering, Hexagone)

- (Laboratory of Applied Biomechanics, Université Gustave Eiffel)

- (Laboratory of Applied Biomechanics, Université Gustave Eiffel)

## Endorsed by

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European Society
of Biomechanics

## Sponsored by

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Oasys
LS-DYNA ENVIRONMENT

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ALTAIR

JSOL
# Predicting Early-Stage Damage in Pelvic Soft Tissues Using Hyper-Viscoelastic Modeling

A.S Caro¹(*) and S. Iaquinta¹

¹ LMGC, IMT Mines Ales, Univ Montpellier, CNRS, Ales, France

**Keywords:** perineal skin; hyperviscoelasticity; Mullins effect, Relaxation, Damage

## 1. Introduction

The pelvic floor supports pelvic organs but is prone to Pelvic Floor Dysfunctions, affecting up to 32% of women worldwide. Factors such as age, menopause, and traumatic events like perineal tears during childbirth significantly contribute to these dysfunctions (Jansson et al., 2020). Preventing these tears may be possible through anticipation. In our team, we aim to achieve this by monitoring the in-situ evolution of parameters (such as viscosity) and identifying indicators that could indicate pre-damage before it becomes visible (tissue degradation, holes). The first step, and the focus of this presentation, is to conduct cyclic tensile tests on porcine perineal tissues to characterize the hyper-viscoelastic behavior and the stress softening phenomenon.

## 2. Methods

Skin tissues were extracted after dissection from porcine perinea supplied by the local slaughterhouse in Alès (SEMAAC). Rectangular shapes were sampled from tissues of pig perineum. Instrumented pure-shear tests were conducted under a constant strain speed of 0.03s⁻¹. The test consisted in applying cycles every 10% of elongation, each cycle being composed of traction, relaxation and unloading phases. Digital Image Correlation (DIC) enabled the evaluation of the in-plane strain tensor (Fig. 1)(Caro-Bretelle et al., 2016).

<figure><img src="image_13.png" /><figcaption>Figure 1 Device, sample geometry and pure shear stress versus elongation</figcaption></figure>

A visco-hyperelastic incompressible constitutive model, which generalizes the Zener's model in large strain (Rebouah & Chagnon, 2014), allows us to express the global fitst Piola-Kirchhoff stress tensor in terms of hyperelastic ($\bar{S}_{iso}$), viscous ($\bar{Q}$) and volumic $\bar{S}_{vol}$ components:

$$ \bar{S} = \bar{S}_{iso} + \bar{Q} + \bar{S}_{vol} $$

with $\tau \bar{Q} + \bar{Q} = \tau \beta \bar{S}_{iso}$, $\bar{Q}(t = 0) = 0$, where $\tau$ is the relaxation time in second and $\beta$ is an adimensional energetic parameter. The originality of this presentation is that the viscous parameters depend on the applied strain.

## 3. Results and Discussion

An optimization procedure allows us to fit experimental data with the proposed modelling. The evolution of the viscous parameters is shown in Fig. 2 for a testing on skin tissues from 3 different pigs.

<figure><img src="image_14.png" /><figcaption>Figure 2 Time relaxation evolutions as a function of elongation</figcaption></figure>

## 4. Conclusions

Evolutive viscous parameters appear to be effective in describing pre-damage in porcine soft tissues, as they provide good reproducibility and exhibit a change in behaviour as the tissue approaches a damaged state.

## References

Caro-Bretelle, A. S., Ienny, P., et al, 2016, Constitutive modeling of stress softening and permanent set in a porcine skin tissue: Impact of the storage preservation. Journal of Biomechanics, 49(13), 2863-2869

Jansson, M. H., Franzén, et al, 2020, Risk factors for perineal and vaginal tears in primiparous women, BMC Pregnancy and Childbirth, 20(1), 749.

Rebouah, M., & Chagnon, G., 2014, Extension of classical viscoelastic models in large deformation to anisotropy and stress softening. International Journal of Non-Linear Mechanics, 61, 54-64.

<footnote>*Corresponding author. Email: Anne-Sophie.Caro@mines-ales</footnote>