# Fresh human stomach tissue: mechanical and microstructural insight

François Fournier, Wei Wei, Thierry Bège, Catherine Masson

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François Fournier, Wei Wei, Thierry Bège, Catherine Masson. Fresh human stomach tissue: mechanical and microstructural insight. Multidisciplinary Biomechanics Journal, 2025, 50th congress of the., 10.46298/mbj.16209. hal-05191762v2

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<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Fresh human stomach tissue: mechanical and microstructural insight

François Fournier<sup>a*</sup>, Wei Wei<sup>a</sup>, Thierry Bège<sup>a, b</sup>, Catherine Masson<sup>a</sup>

a Univ Gustave Eiffel, Aix-Marseille Univ, LBA, Marseille, France

b Service de chirurgie générale et digestive, CHU Nord AP-HM, Aix-Marseille université, Marseille, France

* Corresponding author: francois.fournier@univ-eiffel.fr

Received date: 05/04/2025

Accepted date: 27/06/2025

Publication date: 27/10/2025

Keywords: biaxial tensile testing, stomach biomechanics, microstructure, sleeve gastrectomy

© 2025 The Authors
Licence CC-BY 4.0
Published by Société de Biomécanique

## 1. Introduction

Sleeve gastrectomy has become the predominant bar- iatric procedure in France, representing 52 500 sur- geries in 2018, with a significant increase from only 2800 surgeries in 1997 (Oberlin and de Peretti, 2020). It is always unclear how this procedure affects stom- ach functional mechanics. With objective in a second stage to develop an accurate numerical model, we need first accurate experimental data on the structure of stomach wall. This research aims to characterize comprehensively the mechanical behavior of human stomach tissue from the fundus region through biaxial tensile testing complemented by quantitative histological analysis of fiber orientation and dispersion, consistent with recent studies on gastric tissue biomechanics (Fournier et al., 2024).

## 2. Methods

### 2.1 Tissue preparation

Human stomach tissue samples, approximately 35×35 mm, were excised from the fundus region of stomachs obtained from six patients (BMI of 41.2±4.2 kg/m² and 40.5±17.5-year-old) undergoing sleeve gastrec- tomy. Specimens were stored in phosphate-buffered saline (PBS) at 4°C and mechanically tested within six hours following resection. To ensure consistency, rakes equipped with five stainless steel spikes each were precisely positioned using a standardized guide, defin- ing a test area of 20×20 mm. Sample thickness was

measured on nine points using a laser, and mean value was taken for computation of stress. Circumferential and longitudinal directions were defined with respect to the smaller curvature. Samples were installed in the machine so that axis one was circumferential direction and axis two longitudinal one.

### 2.2 Biaxial testing protocol

Bi-axial tests included three displacement ratios (1:1, 1:2, 2:1, with first axis circumferential and second lon- gitudinal) at two strain rates (0.01, 0.1 s⁻¹), with each sample undergoing five tests to 30% strain followed by a destructive test to failure (always 1:1, 0.01 s⁻¹). Preloading (0.02 N per axis) and five preconditioning cycles (±1 mm displacement at testing speed) were applied prior to each test. Continuous hydration was maintained using PBS spray.

Cauchy stress was computed using incompressibility hypothesis:

$$ \lambda_3 = \frac{1}{(\lambda_1 \cdot \lambda_2)} \quad (\text{incompressibility}) $$

Leading to:

$$ \sigma_{Cauchy} = \left(\frac{F}{A_0}\right) \lambda_1 \cdot \lambda_2 $$

With $\lambda_1$, $\lambda_2$ in plane stretch, $\lambda_3$ out of plane, F measured force and $A_0$ undeformed cross-sectional area.
a.

fundus 0.01 s⁻¹ (0.1 mm/s/arm) (≤ 30%)

<figure><img src="image_2.png" /></figure>

fundus 0.1 s⁻¹ (1 mm/s/arm) (≤ 30%)

<figure><img src="image_3.png" /></figure>

b.

fundus - Destructive (1:1 0.01 s⁻¹ (0.1 mm/s/arm))

<figure><img src="image_4.png" /></figure>

c.

<figure><img src="image_5.png" /></figure>

**Figure 1.** (a) Biaxial tensile tests result on fundus samples at different strain rates (0.01 and 0.1 s⁻¹) and loading ratios (1:1, 1:2, 2:1). (b) Equibiaxial tests until damage with automated damage detection. (c) Collagen fiber orientation from quantitative histological analysis (0°-180° being circumferential direction).

## 2.3 Damage detection

Tissue damage initiation was identified through a three-segment linear fitting of stress-strain curves, performed specifically on the destructive tests. Damage onset was determined at the intersection between the second and third linear segments.

## 2.4 Microstructure analysis

Histological analyses involved staining tissue sections to identify collagen (Masson's Trichrome), elastin (Orcein), and smooth muscle fibers (immunohistochemical staining for smooth muscle actin). Fiber segmentation was performed using a semi-automated MATLAB-based approach employing color thresholds. Fiber orientations were quantitatively assessed through ellipse fitting using MATLAB's region properties function as described by Fournier et al. (2024).

## 3. Results and discussion

A total of nine specimens were tested from the fundus region. Experimental stress-strain curves are presented in Figure 1 a. for non-destructive tests at different ratios and speeds and in Figure 1 b. for destructive tests, with automated damage detection. Strain rate variation reveals a clear strain-rate hardening behavior.

Strain, longitudinal and circumferential stress at damage are presented in Table 1. While statistical difference is not obtained due to the small number of samples, stress values at damage in longitudinal and circumferential direction suggest slight anisotropy in the damage mechanism with a substantial variability between specimens.

Microstructural quantification is presented Figure 1c. with collagen fibres being oriented mainly circumferentially. This direction with small dispersion confirms
that the observed anisotropic behaviour could come from fibre orientation in the microstructure.

<table><caption>**Table 1.** Strain and stress at beginning of damage for tested samples in fundus regions</caption><thead><tr><th rowspan="2">Region</th><th rowspan="2">Strain</th><th colspan="2">Stress (MPa)</th></tr><tr><th>Circumferential</th><th>Longitudinal</th></tr></thead><tbody><tr><td>fundus</td><td>1.00 ± 0.27</td><td>0.05 ± 0.03</td><td>0.06 ± 0.04</td></tr></tbody></table>

The use of different loading ratios provided valuable insight on anisotropy and in-plane mechanical coupling, for example with a 1:1 ratio being more rigid in than 2:1 and less than 1:2 at 0.01 s⁻¹, which would be beneficial for complex hyperelastic anisotropic material model fitting.

While not presented here, a comparison with data obtained from corpus region could help understand if this anisotropic behaviour is region depended, and if it could be linked with physiological function of the stomach as suggested by Papenkort et al., 2024 on porcine stomachs.

## 4. Conclusions

This study provides a comprehensive characterization of human stomach fundus region tissue mechanics following sleeve gastrectomy, combining biaxial testing with quantitative histological analysis. Our findings will directly inform the development of advanced constitutive models, particularly the Holzapfel-Gasser-Ogden (HGO) model, which can capture the anisotropic, fiber-reinforced nature of stomach tissue (Gasser et al., 2006; Holzapfel et al., 2000).

Future work will extend this analysis to other stomach regions and incorporate Digital Image Correlation (DIC) techniques to validate finite element strain fields and refine parameter fitting for computationally robust constitutive models.

## Acknowledgements

The authors acknowledge the surgical teams for providing stomach tissue samples and the laboratory technical staff for their assistance with the data acquisition.

## Conflict of Interest Statement

None.

## Contributor Roles

FF: Conceptualization, Methodology, Writing original draft, experimental data acquisition and processing;

WW: Conceptualization, Methodology, Validation, Writing-review & editing; TB: Conceptualization, Methodology, Sample extraction, Validation, Writing-review & editing; CM: Conceptualization, Methodology, experimental data acquisition, Validation, Writing-review & editing.

## Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

## References

* Oberlin, P., & de Peretti, C. (2020). Bariatric Surgery in France from 1997 to 2018. *Surgery for Obesity and Related Diseases, 16*, 1069–1077. https://doi.org/10.1016/j.soard.2020.04.022

* Fournier, F., Bège, T., Dales, J.-P., Wei, W., & Masson, C. (2024). Unravelling the mechanics of gastric tissue: A comparison of constitutive models, damage probability and microstructural insights. *Journal of the Mechanical Behavior of Biomedical Materials, 160*, 106712. https://doi.org/10.1016/j.jmbbm.2024.106712

* Papenkort, S., Borsdorf, M., Kiem, S., Böl, & M., Siebert, T. (2024). Regional differences in stomach stretch during organ filling and their implications on the mechanical stress response. *Journal of Biomechanics, 168*, 112107. https://doi.org/10.1016/j.jbiomech.2024.112107

* Gasser, T. C., Ogden, R. W., & Holzapfel, G. A. (2006). Hyperelastic modelling of arterial layers with distributed collagen fibre orientations. *J. R. Soc. Interface, 3*, 15–35. https://doi.org/10.1098/rsif.2005.0073

* Holzapfel, G. A. (2000). *Nonlinear solid mechanics: a continuum approach for engineering*. New York: Wiley, Chichester.