Characterization of non-linear mechanical behavior of the cornea

A Ashofteh Yazdi,G Rus,A Callejas,M Gonzalez-Andrades,J Melchor,I Faris,J Torres

doi:10.1038/s41598-020-68391-7

A Ashofteh Yazdi, G Rus + Show 5 more

Open Access

https://doi.org/10.1038/s41598-020-68391-7

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Abstract

The objective of this study was to evaluate which hyperelastic model could best describe the non-linear mechanical behavior of the cornea, in order to characterize the capability of the non-linear model parameters to discriminate structural changes in a damaged cornea. Porcine corneas were used, establishing two different groups: control (non-treated) and NaOH-treated (damaged) corneas (n = 8). NaOH causes a chemical burn to the corneal tissue, simulating a disease associated to structural damage of the stromal layer. Quasi-static uniaxial tensile tests were performed in nasal-temporal direction immediately after preparing corneal strips from the two groups. Three non-linear hyperelastic models (i.e. Hamilton-Zabolotskaya model, Ogden model and Mooney-Rivlin model) were fitted to the stress–strain curves obtained in the tensile tests and statistically compared. The corneas from the two groups showed a non-linear mechanical behavior that was best described by the Hamilton-Zabolotskaya model, obtaining the highest coefficient of determination (R2 > 0.95). Moreover, Hamilton-Zabolotskaya model showed the highest discriminative capability of the non-linear model parameter (Parameter A) for the tissue structural changes between the two sample groups (p = 0.0005). The present work determines the best hyperelastic model with the highest discriminative capability in description of the non-linear mechanical behavior of the cornea.

Highlights

The objective of this study was to evaluate which hyperelastic model could best describe the nonlinear mechanical behavior of the cornea, in order to characterize the capability of the non-linear model parameters to discriminate structural changes in a damaged cornea
We propose that non-linear mechanical parameters can be obtained from non-invasive elastography or probing technologies such as non-linear torsional waves, non-linearity in probing, non-linearity by micro-indentation to be used in diagnostics in-vivo without removing the c ornea[7,8,9]
As the collagen structure is directly tied to the biomechanical properties, it is expected that mechanical properties will vary in the axial d irection[23]

Summary

Introduction

The objective of this study was to evaluate which hyperelastic model could best describe the nonlinear mechanical behavior of the cornea, in order to characterize the capability of the non-linear model parameters to discriminate structural changes in a damaged cornea. The corneas from the two groups showed a non-linear mechanical behavior that was best described by the Hamilton-Zabolotskaya model, obtaining the highest coefficient of determination (R2 > 0.95). Corneal ectasia or corneal ectatic disorders stand as a main priority because of their incidence and impact in young population These are corneal disorders, such as keratoconus or pellucid marginal corneal degeneration, that cause alterations in the corneal structure, leading to corneal topographical changes with decreased corneal thickness and abnormal corneal c urvature[3]. Non-linear models might facilitate to understand how corneal diseases affect the structure and the mechanical behavior of the cornea, and how this leads to blurred vision, or even blindness, in combination with other strategies. Ye et al (2018) introduced a finite element formulation to show the non-linear behavior of finite amplitude shear waves in soft solids, considering a visco-hyperelastic Landau’s m odel[27]

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