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An indentation method to determine the properties of hyperelastic thin films is proposed, which is to use a spherical indenter to indent on the film with a small circular hole in the center. During this progress, there exists a maximum indentation load before penetration. Considering geometries of the film and the indenter, the specific form of relationship between the maximum indentation load and the elastic properties of the film is developed for neo-Hookean, Arruda-Boyce, and Ogden hyperelastic constitutive models. On the basis of this relationship, the initial shear modulus of the film can be directly obtained from single data of the maximum load, instead of recording and fitting to indentation curves. Furthermore, other properties of hyperelastic materials are explored from the perspective of the inverse problem. The experiments are performed with natural rubber, silicone rubber, and polydimethylsiloxane (PDMS) films to verify the feasibility of our method, and the optimal radius ratio between the indenter and the hole is concluded from the experimental results. [ABSTRACT FROM AUTHOR]

Artificial meat is an eco-friendly alternative to real meat that is marketed to have a similar taste and feel. The mechanical properties of artificial meat significantly influence our perception of taste, but how precisely the mechanics of artificial meat compare to real meat remains insufficiently understood. Here we perform mechanical tension, compression, and shear tests on isotropic artificial meat (Tofurky® Plant-Based Deli Slices), anisotropic artificial meat (Daring™ Chick'n Pieces) and anisotropic real meat (chicken) and analyze the data using constitutive neural networks and automated model discovery. Our study shows that, when deformed by 10%, artificial and real chicken display similar maximum stresses of 21.0 kPa and 21.8 kPa in tension, -7.2 kPa and -16.4 kPa in compression, and 2.4 kPa and 0.9 kPa in shear, while the maximum stresses for tofurky were 28.5 kPa, -38.3 kP, and 5.5 kPa. To discover the mechanics that best explain these data, we consulted two constitutive neural networks of Ogden and Valanis–Landel type. Both networks robustly discover models and parameters to explain the complex nonlinear behavior of artificial and real meat for individual tension, compression, and shear tests, and for all three tests combined. When constrained to the classical neo Hooke, Blatz Ko, and Mooney Rivlin models, both networks discover shear moduli of 94.4 kPa for tofurky, 35.7 kPa for artificial chick'n, and 21.4 kPa for real chicken. Our results suggests that artificial chicken succeeds in reproducing the mechanical properties of real chicken across all loading modes, while tofurky does not, and is about three times stiffer. Strikingly, all three meat products display shear softening and their resistance to shear is about an order of magnitude lower than their resistance to tension and compression. We anticipate our study to inspire more quantitative, mechanistic comparisons of artificial and real meat. Our automated-model-discovery based approach has the potential to inform the design of more authentic meat substitutes with an improved perception of taste, with the ultimate goal to reduce environmental impact, improve animal welfare, and mitigate climate change, while still offering the familiar taste and texture of traditional meat. Our source code, data, and examples are available at https://github.com/LivingMatterLab/CANNs. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper presents the results of the comparison between a proposed Fourth Order Elastic Constants (FOECs) nonlinear model defined in the sense of Landau's theory, and the two most contrasted hyperelastic models in the literature, Mooney–Rivlin, and Ogden models. A mechanical testing protocol is developed to investigate the large-strain response of ex vivo cervical tissue samples in uniaxial tension in its two principal anatomical locations, the epithelial and connective layers. The final aim of this work is to compare the reconstructed shear modulus of the epithelial and connective layers of cervical tissue. According to the obtained results, the nonlinear parameter A from the proposed FOEC model could be an important biomarker in cervical tissue diagnosis. In addition, the calculated shear modulus depended on the anatomical location of the cervical tissue ( μ e p i t h e l i a l = 1.29 ± 0.15 MPa, and μ c o n n e c t i v e = 3.60 ± 0.63 MPa). [ABSTRACT FROM AUTHOR]

Plantar soft tissue stiffening in diabetes leads to a risk of developing ulcers. There are relatively few studies providing methods for quantifying the mechanical properties of skin and fat in the plantar tissue of diabetic patients. Previous studies used linear or non-linear single layer deformable models or linear multi-layer models. This study aimed to investigate the mechanical properties of plantar soft tissue using multi-layer, non-linear models to estimate more accurate mechanical properties in the plantar tissues of diabetic patients. Ten healthy young (HY) subjects, ten healthy old (HO) subjects, and ten old diabetic patients (DB) volunteered for the study. Indentation tests were performed at two sites in the heel. The subjects underwent computed tomography (CT) to measure the respective thicknesses of the skin and fat at the indentation sites. Subject-specific finite element models were created to estimate the parameters of the first-order Ogden forms of the skin and fat. The initial shear modulus for the fat layer μ F in DB, HO, and HY were 4.68 MPa (±0.87), 2.71 MPa (±1.25), and 2.27 MPa (±0.87), respectively. The initial shear modulus for the skin layer (μ S) in DB, HO, and HY were 5.86 MPa (±2.51), 7.05 MPa (±1.94), and 14.58 MPa (±1.98), respectively. The DB had stiffer fat tissue than the normal subjects in the same age group but had the same soft skin. These aspects can cause different mechanical stress conditions in a diabetic foot than in a normal foot under the same mechanical loading, making the diabetic foot vulnerable to the initiation of mechanical breakdowns such as ulcers. [ABSTRACT FROM AUTHOR]

Fish gelatin extracted from tilapia (Oreochromis niloticus) skins was used to investigate the large deformation behaviors of gelatin gels (2, 4 and 6.67 g/100 g H 2 O) under uniaxial compression as affected by sugars (0, 5, 10, 15 and 20 g/100 g H 2 O) including sucrose, glucose and fructose. The first order Ogden model was applied to understand the mathematical relationship between the true stress and true strain of tilapia skin gelatin (TSG) gels under large compression deformation (stretch ratio λ = 0.35–1). The results indicated that the addition of sucrose, glucose or fructose in a TSG gel led to a decrease in the gel strength, but the extent of this gel-weakening effect depended on the types and concentrations of sugar. The first order Ogden models fitted very well with the compression responses of TSG gels with or without sugar (R 2 = 0.9949–0.9998). Significant difference (p < 0.05) in the initial shear modulus (μ) and/or the Ogden constant were found among TSG gels with a specific gelatin concentration but different levels of a sugar. The reduction of the μ value was as much as 11–22% for TSG-sugar gels compared to the corresponding gels without sugar. There were power law relationships between the μ values and gelatin concentrations (μ ∝ c 1.49 − 1.65 ) for TSG-sugar gels. This study showed the great fit of the Ogden model for the large deformation responses of gelatin gels and the gel-weakening effects of sugars, which is of significant importance from both theoretical and application aspects. Image 1088 • Large deformation behaviors of gelatin gels as affected by sugars were studied. • The Ogden models fitted well (R2 ≥ 0.995) with the gels' compression responses. • Adding sucrose, glucose or fructose led to a decrease in the gel strength. • The gel-weakening effect of a sugar depended on the sugar type and its amount. [ABSTRACT FROM AUTHOR]