Shear Behavior of Bovine Scleral Tissue

Argento, A.; Kim, Wonsuk; Rozsa, Frank W.; DeBolt, Kori L.; Zikanova, Sophia; Richards, Julia R.

doi:10.1115/1.4027615

Cited by 6 publications

(4 citation statements)

References 74 publications

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“…Though this relationship is well-characterized for tendons, ligaments, cornea and other tissues [2, 24-26, 28, 45], it remains still not fully characterized on sclera. Our results herein are consistent with our previous cross-sectional study of collagen waviness in ONHs fixed at various IOPs [16] and with those of other groups [46, 47].…”

Section: Discussionsupporting

confidence: 93%

Stretch-Induced Uncrimping of Equatorial Sclera Collagen Bundles

Jan

Lee

Wallace

et al. 2022

Preprint

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Stretch-induced collagen uncrimping underlies the nonlinear mechanical behavior of the sclera according to what is often called the process of recruitment. We recently reported experimental measurements of sclera collagen crimp and pressure-induced uncrimping. Our studies, however, were cross-sectional, providing statistical descriptions of crimp with no information on the effects of stretch on specific collagen bundles. Data on bundle-specific uncrimping is necessary to better understand the effects of macroscale input on the collagen microscale and tissue failure. Our goal in this project was to measure bundle-specific stretch-induced collagen uncrimping of sclera. Three goat eyes were cryosectioned sagittally (30 μm). Samples of equatorial sclera were isolated, mounted to a custom uniaxial stretcher and imaged with polarized light microscopy at various levels of clamp-to-clamp stretch until failure. At each stretch level, local strain was measured using image tracking techniques. The level of collagen crimping was determined from the bundle waviness, defined as the circular standard deviation of fiber orientation along a bundle. Eye-specific recruitment curves were then computed using eye-specific waviness at maximum stretch before sample failure to define fibers as recruited. Nonlinear mixed effect models were used to determine the associations of waviness to local strain and recruitment to clamp-to-clamp stretch. Waviness decreased exponentially with local strain (p<0.001), whereas bundle recruitment followed a sigmoidal curve with clamp-to-clamp stretch (p<0.001). Individual bundle responses to stretch varied substantially, but recruitment curves were similar across sections and eyes. In conclusion, uniaxial stretch caused measurable bundle-specific uncrimping, with the sigmoidal recruitment pattern characteristic of fiber-reinforced soft tissues.

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Section: Discussionsupporting

confidence: 93%

Stretch-Induced Uncrimping of Equatorial Sclera Collagen Bundles

Jan

Lee

Wallace

et al. 2022

Preprint

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“…An important result from this study was the quantification of shear strains in the intact peripapillary sclera during increases of IOP. Using shear testing on dissected bovine scleral specimens, a previous study showed that the posterior sclera had a stiffer response to in-plane shear compared to out-of-plane shear [33]. Our results showed that the maximum shear was primarily out-ofplane (in the planes formed by the meridional and throughthickness directions) and at an angle about 45 deg to the scleral surface ( Fig.…”

Section: Discussionsupporting

confidence: 49%

Three-Dimensional Strains in Human Posterior Sclera Using Ultrasound Speckle Tracking

Pavlatos

Perez

Morris

et al. 2016

Journal of Biomechanical Engineering

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Intraocular pressure (IOP) induced strains in the peripapillary sclera may play a role in glaucoma progression. Using inflation testing and ultrasound speckle tracking, the 3D strains in the peripapillary sclera were measured in nine human donor globes. Our results showed that the peripapillary sclera experienced through-thickness compression and meridional stretch during inflation, while minimal circumferential dilation was observed when IOP was increased from 10 to 19 mmHg. The maximum shear was primarily oriented in the through-thickness, meridional cross sections and had a magnitude slightly larger than the first principal strain. The tissue volume had minimal overall change, confirming near-incompressibility of the sclera. Substantial strain heterogeneity was present in the peripapillary region, with local high strain areas likely corresponding to structural heterogeneity caused by traversing blood vessels. These 3D strain characteristics provide new insights into the biomechanical responses of the peripapillary sclera during physiological increases of IOP. Future studies are needed to confirm these findings and investigate the role of these biomechanical characteristics in ocular diseases.

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“…The variations in matrix composition would most likely contribute to spatial variations in the matrix stiffness that were ignored in our model. In a recent study characterizing the shear behavior of the bovine sclera, Argento et al [ 50 ] showed that the in-plane shear modulus was 50% larger in the peripheral sclera than in the peripapillary sclera. Assuming position-dependent matrix and collagen fibers stiffness in our model would have considerably increased the computational cost of the inverse method may have led to the existence of multiple minima to the cost function.…”

Section: Discussionmentioning

confidence: 99%

Glaucoma-related Changes in the Mechanical Properties and Collagen Micro-architecture of the Human Sclera

et al. 2015

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ObjectiveThe biomechanical behavior of the sclera determines the level of mechanical insult from intraocular pressure to the axons and tissues of the optic nerve head, as is of interest in glaucoma. In this study, we measure the collagen fiber structure and the strain response, and estimate the material properties of glaucomatous and normal human donor scleras.MethodsTwenty-two posterior scleras from normal and diagnosed glaucoma donors were obtained from an eyebank. Optic nerve cross-sections were graded to determine the presence of axon loss. The specimens were subjected to pressure-controlled inflation testing. Full-field displacement maps were measured by digital image correlation (DIC) and spatially differentiated to compute surface strains. Maps of the collagen fiber structure across the posterior sclera of each inflated specimen were obtained using synchrotron wide-angle X-ray scattering (WAXS). Finite element (FE) models of the posterior scleras, incorporating a specimen-specific representation of the collagen structure, were constructed from the DIC-measured geometry. An inverse finite element analysis was developed to estimate the stiffness of the collagen fiber and inter-fiber matrix.ResultsThe differences between glaucoma and non-glaucoma eyes were small in magnitude. Sectorial variations of degree of fiber alignment and peripapillary scleral strain significantly differed between normal and diagnosed glaucoma specimens. Meridional strains were on average larger in diagnosed glaucoma eyes compared with normal specimens. Non-glaucoma specimens had on average the lowest matrix and fiber stiffness, followed by undamaged glaucoma eyes, and damaged glaucoma eyes but the differences in stiffness were not significant.ConclusionThe observed biomechanical and microstructural changes could be the result of tissue remodeling occuring in glaucoma and are likely to alter the mechanical environment of the optic nerve head and contribute to axonal damage.

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Shear Behavior of Bovine Scleral Tissue

Cited by 6 publications

References 74 publications

Stretch-Induced Uncrimping of Equatorial Sclera Collagen Bundles

Stretch-Induced Uncrimping of Equatorial Sclera Collagen Bundles

Three-Dimensional Strains in Human Posterior Sclera Using Ultrasound Speckle Tracking

Glaucoma-related Changes in the Mechanical Properties and Collagen Micro-architecture of the Human Sclera

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