Rate dependent biomechanical properties of corneal stroma in unconfined compression

AbstractCompared to articular cartilage, the biomechanical properties of costal cartilage have not yet been extensively explored. The research presented addresses this problem by studying for the first time the anisotropic elastic behavior of human costal cartilage. Samples were taken from 12 male and female cadavers and unconfined compression and indentation tests were performed in mediolateral and dorsoventral direction to determine Young’s Moduli EC for compression and Ei5%, Ei10% and Eimax at 5%, 10% and maximum strain for indentation. Furthermore, the crack direction of the unconfined compression samples was determined and histological samples of the cartilage tissue were examined with the picrosirius-polarization staining method. The tests revealed mean Young’s Moduli of EC = 32.9 ± 17.9 MPa (N = 10), Ei5% = 11.1 ± 5.6 MPa (N = 12), Ei10% = 13.3 ± 6.3 MPa (N = 12) and Eimax = 14.6 ± 6.6 MPa (N = 12). We found that the Young’s Moduli in the indentation test are clearly anisotropic with significant higher results in the mediolateral direction (all P = 0.002). In addition, a dependence of the crack direction of the compressed specimens on the load orientation was observed. Those findings were supported by the orientation of the structure of the collagen fibers determined in the histological examination. Also, a significant age-related elastic behavior of human costal cartilage could be shown with the unconfined compression test (P = 0.009) and the indentation test (P = 0.004), but no sex effect could be detected. Those results are helpful in the field of autologous grafts for rhinoplastic surgery and for the refinement of material parameters in Finite Element models e.g., for accident analyses with traumatic impact on the thorax.

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Preparation and Biomechanical Properties of an Acellular Porcine Corneal Stroma

Cornea ◽

10.1097/ico.0000000000001319 ◽

2017 ◽

Vol 36 (11) ◽

pp. 1343-1351 ◽

Cited By ~ 9

Author(s):

Qing Li ◽

Hongmei Wang ◽

Zhenye Dai ◽

Yichen Cao ◽

Chuanyu Jin

Keyword(s):

Corneal Stroma ◽

Biomechanical Properties

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On Unconfined Compression Response of the Porcine Corneal Stroma

Volume 1B: Extremity; Fluid Mechanics; Gait; Growth, Remodeling, and Repair; Heart Valves; Injury Biomechanics; Mechanotransduction and Sub-Cellular Biophysics; MultiScale Biotransport; Muscle, Tendon and Ligament; Musculoskeletal Devices; Multiscale Mechanics; Thermal Medicine; Ocular Biomechanics; Pediatric Hemodynamics; Pericellular Phenomena; Tissue Mechanics; Biotransport Design and Devices; Spine; Stent Device Hemodynamics; Vascular Solid Mechanics; Student Paper and Design Competitions ◽

10.1115/sbc2013-14795 ◽

2013 ◽

Author(s):

Ebitimi Etebu ◽

Hamed Hatami-Marbini

Keyword(s):

Mechanical Properties ◽

Lattice Structure ◽

Research Work ◽

Corneal Stroma ◽

Swelling Pressure ◽

Transversely Isotropic ◽

Collagen Fibrils ◽

Mechanical Parameters ◽

Unconfined Compression ◽

Biphasic Model

The corneal stroma constitutes about 90% of the corneal total thickness and is mainly responsible for its mechanical properties. The stroma is a highly ordered structure composed of mostly parallel to the surface stacks of 2 μm thick collagenous lamellae. The collagen fibrils have an almost uniform diameter and are arranged in a pseudohexagonal lattice structure. Under normal physiological conditions, the collagen fibrils are responsible for carrying the membrane tensile stresses caused by the intraocular pressure. It is believed that the interaction between the collagen fibrils and hydrophilic negatively charged proteoglycans are responsible for the stromal architecture as well as the compressive properties of the tissue. Up to date uniaxial strip testing method and biaxial pressure inflation experiments have widely been used to determine the mechanical parameters of the cornea. These experimental measurements often provide the necessary information for characterizing the tissue behavior in tension [1] [2, 3]. Nevertheless, the mechanical parameters of the cornea in compression have received less attention in the literature. Most of the previous studies are focused on describing the swelling pressure and hydration relations [4]. In this research work, we used unconfined compression experiments along with a biphasic model to measure the corneal parameters in compression. This method has been extensively used to explore the mechanical properties of similar hydrated tissues such as the articular cartilage [5]. Due to specific microstructure of the cornea, a transversely isotropic model was used to curve-fit the experimental data and to derive the in-plane modulus of the cornea. The predicted in-plane modulus was compared to the values reported in literature.

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Depth Dependent In-Plane Shear Properties of the Corneal Stroma

ASME 2010 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2010-19302 ◽

2010 ◽

Author(s):

Steven Petsche ◽

Peter Pinsky ◽

Dimitri Chernyak ◽

Jaime Martiz

Keyword(s):

Shear Modulus ◽

Patient Outcomes ◽

Surgical Procedures ◽

Refractive Surgery ◽

Corneal Stroma ◽

Shear Stiffness ◽

Biomechanical Properties ◽

Human Cornea ◽

Plane Shear ◽

Biomechanical Response

The popularity of refractive surgery to correct the vision of individuals with hyperopia or myopia is increasing. These procedures alter the tissue of the human cornea to cause a change in curvature (refractive power) of the cornea. Radial keratotomy, photorefractive keratectomy, LASIK, and LASEK are all types of refractive surgery. The outcomes of refractive surgical procedures must depend significantly on the biomechanical response of the tissue and therefore on the biomechanical properties of the cornea, or more specifically the corneal stroma which makes up 90% of the tissue. The missing link between computer models of these procedures and predicting patient outcomes is the biomechanical properties of the tissue, including shear modulus. This study aims to characterize the in-plane shear modulus of the corneal stroma through the depth by mechanical testing. Scant data, if any, exists about the shear stiffness and no data includes depth dependence. The stroma consists of sheets of collagenous lamellae in which fibrils are maintained at uniform spacing by glycoaminoglycan molecules. Studies have shown increased interweaving of the lamellae in the anterior third of the stroma compared to the central and posterior thirds [1]. Figure 1 shows the distinct interweaving in the anterior third [2]. It is hypothesized that more interweaving lamellae increases the in-plane shear stiffness. The shear modulus of the full cornea, as well as individual thirds, is examined in this study.

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Strain-rate Dependent Stiffness of Articular Cartilage in Unconfined Compression

Journal of Biomechanical Engineering ◽

10.1115/1.1560142 ◽

2003 ◽

Vol 125 (2) ◽

pp. 161-168 ◽

Cited By ~ 83

Author(s):

L. P. Li ◽

M. D. Buschmann ◽

A. Shirazi-Adl

Keyword(s):

Articular Cartilage ◽

Strain Rate ◽

Compressive Strain ◽

Fluid Pressure ◽

Nonlinear Function ◽

Protective Mechanism ◽

Unconfined Compression ◽

Rate Dependent ◽

Dependent Behavior ◽

Elastic Loading

The stiffness of articular cartilage is a nonlinear function of the strain amplitude and strain rate as well as the loading history, as a consequence of the flow of interstitial water and the stiffening of the collagen fibril network. This paper presents a full investigation of the interplay between the fluid kinetics and fibril stiffening of unconfined cartilage disks by analyzing over 200 cases with diverse material properties. The lower and upper elastic limits of the stress (under a given strain) are uniquely established by the instantaneous and equilibrium stiffness (obtained numerically for finite deformations and analytically for small deformations). These limits could be used to determine safe loading protocols in order that the stress in each solid constituent remains within its own elastic limit. For a given compressive strain applied at a low rate, the loading is close to the lower limit and is mostly borne directly by the solid constituents (with little contribution from the fluid). In contrast, however in case of faster compression, the extra loading is predominantly transported to the fibrillar matrix via rising fluid pressure with little increase of stress in the nonfibrillar matrix. The fibrillar matrix absorbs the loading increment by self-stiffening: the quicker the loading the faster the fibril stiffening until the upper elastic loading limit is reached. This self-protective mechanism prevents cartilage from damage since the fibrils are strong in tension. The present work demonstrates the ability of the fibril reinforced poroelastic models to describe the strain rate dependent behavior of articular cartilage in unconfined compression using a mechanism of fibril stiffening mainly induced by the fluid flow.

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Glycosaminoglycan and Collagen Remodeling During In Vitro Dynamic Compression of Articular Cartilage: Experiments and Finite Element Modeling

Volume 1B: Extremity; Fluid Mechanics; Gait; Growth, Remodeling, and Repair; Heart Valves; Injury Biomechanics; Mechanotransduction and Sub-Cellular Biophysics; MultiScale Biotransport; Muscle, Tendon and Ligament; Musculoskeletal Devices; Multiscale Mechanics; Thermal Medicine; Ocular Biomechanics; Pediatric Hemodynamics; Pericellular Phenomena; Tissue Mechanics; Biotransport Design and Devices; Spine; Stent Device Hemodynamics; Vascular Solid Mechanics; Student Paper and Design Competitions ◽

10.1115/sbc2013-14286 ◽

2013 ◽

Author(s):

Kevin A. Yamauchi ◽

Christopher B. Raub ◽

Albert C. Chen ◽

Robert L. Sah ◽

Scott J. Hazelwood ◽

...

Keyword(s):

Articular Cartilage ◽

Dynamic Compression ◽

Fluid Velocity ◽

Biomechanical Properties ◽

Mechanical Stimuli ◽

Unconfined Compression ◽

Growth Data ◽

Collagen Remodeling ◽

Continuum Mixture Model

The biomechanical properties of articular cartilage (AC) can be altered by chemical and mechanical stimuli. Dynamic unconfined compression (UCC) has been shown to increase biosynthesis at moderate strain amplitudes (1–4%) and frequencies from 0.01Hz. to 0.1Hz [1]. Furthermore, interstitial fluid velocity and maximum principle strain have been proposed as candidates for controlling glycosaminoglycan (GAG) and collagen (COL) remodeling, respectively [2,3]. The goal of this study was to integrate in vitro growth data, including biochemical and microstructural properties, into a computational continuum mixture model to elucidate potential mechanical triggers for AC tissue remodeling.

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Effect of Strain Rate on the Material Properties of Human Liver Parenchyma in Unconfined Compression

Journal of Biomechanical Engineering ◽

10.1115/1.4024821 ◽

2013 ◽

Vol 135 (10) ◽

Cited By ~ 15

Author(s):

Andrew R. Kemper ◽

Anthony C. Santago ◽

Joel D. Stitzel ◽

Jessica L. Sparks ◽

Stefan M. Duma

Keyword(s):

Finite Element ◽

Human Liver ◽

Injury Risk ◽

Loading Rate ◽

Failure Strain ◽

Liver Parenchyma ◽

Failure Stress ◽

Finite Element Models ◽

Unconfined Compression ◽

Rate Dependent

The liver is one of the most frequently injured organs in abdominal trauma. Although motor vehicle collisions are the most common cause of liver injuries, current anthropomorphic test devices are not equipped to predict the risk of sustaining abdominal organ injuries. Consequently, researchers rely on finite element models to assess the potential risk of injury to abdominal organs such as the liver. These models must be validated based on appropriate biomechanical data in order to accurately assess injury risk. This study presents a total of 36 uniaxial unconfined compression tests performed on fresh human liver parenchyma within 48 h of death. Each specimen was tested once to failure at one of four loading rates (0.012, 0.106, 1.036, and 10.708 s−1) in order to investigate the effects of loading rate on the compressive failure properties of human liver parenchyma. The results of this study showed that the response of human liver parenchyma is both nonlinear and rate dependent. Specifically, failure stress significantly increased with increased loading rate, while failure strain significantly decreased with increased loading rate. The failure stress and failure strain for all liver parenchyma specimens ranged from −38.9 kPa to −145.9 kPa and from −0.48 strain to −1.15 strain, respectively. Overall, this study provides novel biomechanical data that can be used in the development of rate dependent material models and the identification of tissue-level tolerance values, which are critical to the validation of finite element models used to assess injury risk.

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A Biphasic Approach for Characterizing Tensile, Compressive, and Hydraulic Properties of the Sclera

10.1101/2020.05.21.108936 ◽

2020 ◽

Author(s):

Dillon M. Brown ◽

Machelle T. Pardue ◽

C. Ross Ethier

Keyword(s):

Association Studies ◽

Compressive Strain ◽

Tensile Modulus ◽

Tensile Tests ◽

Biomechanical Properties ◽

Compression Testing ◽

Compression Tests ◽

Unconfined Compression ◽

Tensile Stiffness ◽

Poroelastic Theory

AbstractMeasuring the biomechanical properties of the mouse sclera is of great interest, since altered scleral properties are features of many common ocular pathologies, and the mouse is a powerful species for studying genetic factors in disease. Here, a poroelastic material model is used to analyze data from unconfined compression testing of both pig and mouse sclera, and the tensile modulus, compressive modulus, and permeability of the sclera are obtained at three levels of compressive strain. Values for all three properties measured simultaneously by unconfined compression of pig sclera were comparable to previously reported values measured by tests specific for each property, i.e., compression tests, biaxial tensile tests, and falling-head permeability assays. The repeatability of the approach was evaluated using test-retest experimental paradigm on pig sclera. Repeatability was low for measured compressive stiffness, indicating permanent changes to the samples occurring after the first test. However, reasonable repeatability for tensile stiffness and permeability was observed. The intrinsic material properties of the mouse sclera were measured for the first time. Tensile stiffness and permeability of the sclera in both species were seen to be dependent on the state of compressive strain. We conclude that unconfined compression testing of sclera, when analyzed with poroelastic theory, can be used as a powerful tool to phenotype mouse scleral changes in future genotype-phenotype association studies.Statement of SignificanceOcular biomechanics is strongly influenced by the sclera, the outermost white coat of the eye. Many ocular diseases are believed to be influenced by pathological changes to scleral microstructure and biomechanics, making intrinsic biomechanical properties an important outcome measure in many studies. However, the small mouse eye precludes the use of most traditional biomechanical characterization techniques. Here, we show that unconfined compression testing analyzed with poroelastic theory can produce measurements of biomechanical properties in the pig sclera comparable to those measured by other traditional techniques. Importantly, this technique can be successfully applied to the mouse sclera, enabling more widespread use of the species as a model for ocular disease.

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