Influence of Ionic Concentration on Swelling Behavior and Shear Properties of the Bovine Cornea

2012 ◽  
Author(s):  
Hamed Hatami-Marbini ◽  
Ebitimi Etebu
Keyword(s):  
Extracellular Matrix ◽  
Dermatan Sulfate ◽  
Core Protein ◽  
Incident Light ◽  
Corneal Stroma ◽  
Ionic Concentration ◽  
Collagen Fibers ◽  
Collagen Fibrils ◽  
Knock Out ◽  
Free Ions

The mechanical properties and structure of connective tissues such as the cornea and the cartilage are derived from the functions and properties of their extracellular matrix, a polyelectrolyte gel composed of collagenous fibers embedded in an aqueous matrix. The collagen fibers in the extracellular matrix of the corneal stroma are arranged in regular lattice structures, which is necessary for corneal transparency and transmitting the incident light to the back of the eye. This regular pseudo hexagonal arrangement is attributed to the interaction of collagen fibers with the proteoglycans as these regularities are lost in knock-out mice [i]. Proteoglycans (PGs) are heavily glycosylated glycoproteins. They consist of a core protein to which is glycosaminoglycan chains are covalently attached. The main PG in the corneal stroma is the proteoglycan decorin. Decorin is the simplest small leucine-rich PG and only has a single glycosaminoglycan side chain. It has a horse shape core protein and binds collagen fibrils at regular sites. Chondroitin sulfate (CS), dermatan sulfate (DS), keratan sulfate (KS) are among the prevalent glycosaminoglycans found in the cornea. Under physiological conditions, these linear carbohydrate polymers are ionized and carry negative charges due to the presence of negatively charged carboxylate and sulfate groups. Therefore, a hydrated gel is formed in the empty space between collagen fibrils by attracting water. The interaction of negatively charged glycosaminoglycans with themselves and their interaction with the free ions contribute to the corneal swelling pressure and subsequently to its compressive stiffness. From structural view point, the corneal stroma is a composite polyelectrolyte system in which the observed regular spacings of the collagens are suggested to exist because of the structural interaction of collagens, negatively charged glycosaminoglycans, and the free ions in the interfibrillar space.

Characterizing Swelling Pressure and Hydration Relationship for Porcine Corneal Stroma

2013 ◽  
Author(s):  
Hamed Hatami-Marbini ◽  
Ebitimi Etebu ◽  
Abdolrasol Rahimi
Keyword(s):  
Extracellular Matrix ◽  
Core Protein ◽  
Lattice Structure ◽  
Incident Light ◽  
Corneal Stroma ◽  
Swelling Pressure ◽  
Collagen Fibrils ◽  
Bathing Solution ◽  
Swelling Properties ◽  
Knock Out

The mechanical properties and structure of connective tissues such as the cornea and articular cartilage are derived from the functions and properties of their extracellular matrix, which is a polyelectrolyte gel composed of collagenous fibers embedded in an aqueous matrix. The collagen fibrils in the extracellular matrix of the corneal stroma are arranged in a regular lattice structure, which is necessary for corneal transparency and transmitting the incident light to the back of the eye. This regular pseudo hexagonal arrangement is attributed to the interaction of collagen fibrils with the proteoglycans; these regularities are lost in proteoglycan knock-out mice [1]. Proteoglycans are heavily glycosylated glycoproteins consisting of a core protein to which glycosaminoglycan chains are covalently attached. The main proteoglycan in the corneal stroma is decorin. Decorin is the simplest small leucine-rich proteoglycan with only a single glycosaminoglycan side chain. It has a horse shape core protein and binds collagen fibrils at regular sites. Under normal physiological conditions, these linear carbohydrate polymers are ionized and carry negative charges due to the presence of negatively charged carboxylate and sulfate groups. The presence of these fixed charges creates an imbalance of charge density within the stroma and its surrounding aqueous domain. Therefore, the tissue has a tendency to swell when immersed in a bathing solution. In order to create mathematical models for the corneal mechanics, a proper experimental characterization of the swelling properties of the tissue is necessary.

Ultrastructural Evidence for Proteoglycans Mediating an Attachment of Type VI Collagen to Banded Collagen Fibrils

1997 ◽  
Vol 3 (S2) ◽  
pp. 153-154
Author(s):  
Douglas R. Keene ◽  
Catherine C. Ridgway ◽  
Renato V. Iozzo
Keyword(s):  
Dermatan Sulfate ◽  
Core Protein ◽  
Solid Phase ◽  
Collagen Fibrils ◽  
Binding Assays ◽  
Connective Tissues ◽  
Type Vi Collagen ◽  
Dermatan Sulfate Proteoglycan ◽  
Individual Type ◽  
Solid Phase Binding

Immunolocalizaton studies of type VI collagen in skin have previously demonstrated that type VI collagen forms a flexible network that anchors large interstitial structures such as nerves, blood vessels, and collagen fibers into the surrounding connective tissues matrix. The purpose of this study is to determine if individual type VI collagen microfilaments might be connected to banded collagen fibrils, thereby stabilizing the network.Solid phase binding assays suggest a specific, high affinity interaction between the core protein of the dermatan sulfate proteoglycan decorin and type VI collagen, and immunocytochemical studies in fetal and neonate rabbit cornea suggest an association of decorin with type VI microfilaments. Other studies in skin and perichondrium have localized decorin to a region between the d and e bands of banded collagen fibrils. However, no direct documentation has demonstrated a specific structural interaction between type VI microfilaments and banded collagen fibrils. We, therefore, sought to determine if type VI microfilaments cross banded collagen fibrils between the “d” and “e” bands.

Electrostatic Contribution of the Proteoglycans to the In-Plane Shear and Compressive Stiffness of Corneal Stroma

2010 ◽  
Author(s):  
Hamed Hatami-Marbini ◽  
Peter M. Pinsky
Keyword(s):  
Extracellular Matrix ◽  
Articular Cartilage ◽  
Electrostatic Interactions ◽  
Corneal Stroma ◽  
Collagen Fibers ◽  
Connective Tissues ◽  
Compressive Stiffness ◽  
Electrostatic Contribution ◽  
Repulsive Forces

The extracellular matrix (ECM) is a fibrous structure embedded in an aqueous gel. The mechanical and electrostatic interactions of the ECM constituents, i.e. collagen fibers and proteoglycans (PGs), define the structure and mechanical response of connective tissues (CTs) such as cornea and articular cartilage. Proteoglycans are complex macromolecules consisting of linear chains of repeating gylcosaminoglycans (GAGs) which are covalently attached to a core protein. PGs can be as simple as decorin with a single GAG side chain or as complex as aggrecan with many GAGs. Decorin is the simplest small leucine-rich PG and is the main PG inside the corneal stroma. It has an arch shape and links non-covalently at its concave surface to the collagen fibrils. It has been shown that while collagen fibers inside the extracellular matrix resist the tensile forces, the negatively charged glycosaminoglycans and their interaction with water give compressive stiffness to the tissue. The role of PGs in biomechanical properties of the connective tissues has mainly been studied in order to explore the behavior of articular cartilage [1], which is a CT with large and highly negatively charged PGs, aggrecans. In order to explain the role of PGs in this tissue, it is commonly assumed that their contribution to the CT elasticity is because of both the repulsive forces between negatively charged GAGs and GAG interactions with free mobile charges in the ionic bath. The electrostatic contribution to the shear and compressive stiffness of cartilage is modeled by approximating GAGs as charged rods [1]. The Poisson-Boltzmann equation is used to compute the change in electrical potential and mobile ion distributions which are caused by the macroscopic deformation.

Material Properties of Porcine Corneal Stroma in Unconfined Compression

2013 ◽  
Author(s):  
Hamed Hatami-Marbini ◽  
Ebitimi Etebu
Keyword(s):  
Extracellular Matrix ◽  
Corneal Stroma ◽  
Swelling Pressure ◽  
Empty Space ◽  
Collagen Fibers ◽  
Necessary Condition ◽  
Internal Stresses ◽  
Connective Tissues ◽  
Polyelectrolyte Gel ◽  
Hexagonal Arrangement

The tensile properties of the cornea have been extensively studied while there are fewer studies on its compressive stiffness. The mechanical properties and structure of the cornea like many other connective tissues are derived from the function and properties of their extracellular matrix. The corneal extracellular matrix, stroma, is a polyelectrolyte gel composed of collagenous fibers embedded in an aqueous matrix. The cornea has two different functions: optical and mechanical. It is the main refractive component of the visual system and it is an effective barrier resisting the deformation caused by external and internal stresses. A necessary condition for corneal optical properties and transparency is the maintenance of a pseudo hexagonal arrangement of the collagen fibers inside the extracellular matrix. This regular arrangement is attributed to the interaction of collagen fibers with the proteoglycans. Under physiological conditions, the proteoglycans are ionized and form a hydrated gel in the empty space between the collagen fibrils by attracting the water and solutes. The interaction of the negatively fixed charges of the proteoglycans with themselves and with the free ions inside the interstitial fluid contributes to the corneal swelling pressure and subsequently to its compressive properties.

scholarly journals Extracellular Matrix Deposition and Remodeling after Corneal Alkali Burn in Mice

2021 ◽  
Vol 22 (11) ◽  
pp. 5708
Author(s):  
Kazadi N. Mutoji ◽  
Mingxia Sun ◽  
Garrett Elliott ◽  
Isabel Y. Moreno ◽  
Clare Hughes ◽  
...  
Keyword(s):  
Extracellular Matrix ◽  
Dermatan Sulfate ◽  
Temporal Distribution ◽  
Keratan Sulfate ◽  
Collagen Fibrils ◽  
Type I ◽  
Chemical Injury ◽  
Matrix Deposition ◽  
Alkali Burn ◽  
Extracellular Matrix Deposition

Corneal transparency relies on the precise arrangement and orientation of collagen fibrils, made of mostly Type I and V collagen fibrils and proteoglycans (PGs). PGs are essential for correct collagen fibrillogenesis and maintaining corneal homeostasis. We investigated the spatial and temporal distribution of glycosaminoglycans (GAGs) and PGs after a chemical injury. The chemical composition of chondroitin sulfate (CS)/dermatan sulfate (DS) and heparan sulfate (HS) were characterized in mouse corneas 5 and 14 days after alkali burn (AB), and compared to uninjured corneas. The expression profile and corneal distribution of CS/DSPGs and keratan sulfate (KS) PGs were also analyzed. We found a significant overall increase in CS after AB, with an increase in sulfated forms of CS and a decrease in lesser sulfated forms of CS. Expression of the CSPGs biglycan and versican was increased after AB, while decorin expression was decreased. We also found an increase in KS expression 14 days after AB, with an increase in lumican and mimecan expression, and a decrease in keratocan expression. No significant changes in HS composition were noted after AB. Taken together, our study reveals significant changes in the composition of the extracellular matrix following a corneal chemical injury.

Heterotypic fibrils and stabilizing collagens in corneal development

1991 ◽  
Vol 49 ◽  
pp. 172-173
Author(s):  
T. F. Linsenmayer ◽  
D. E. Birk ◽  
C. M. Linsenmayer ◽  
M. K. Gordon ◽  
J. K. Marchant ◽  
...  
Keyword(s):  
Extracellular Matrix ◽  
Corneal Stroma ◽  
Collagen Fibrils ◽  
Extracellular Matrix Production ◽  
Different Types ◽  
Corneal Development ◽  
Matrix Production ◽  
Temporal And Spatial ◽  
Molecular Components ◽  
Horizontal Layers

Our studies on the embryonic development of the chick cornea have recently yielded information suggesting possible roles for different types and classes of collagens. The chick cornea develops through a series of precisely controlled temporal and spatial events involving cell differentiation, migration and extracellular matrix production and assembly. Each event involves, and is possibly dictated by, dramatic changes in the major molecular components of the extracellular matrix. Corneal morphogenesis begins with the formation of the primary corneal stroma, a dense subepithelial matrix consisting of orthogonally arranged, horizontal layers of collagen fibrils. Each layer is one fibril thick. This stroma then rapidly swells and immediately thereafter is invaded by pericorneal mesenchymal cells. These cells differentiate into stromal keratocytes and synthesize the secondary, mature stroma, a structure in which each orthogonal layer is many collagen fibrils thick.

Hydration Effects on Tensile Properties of the Corneal Stroma

2013 ◽  
Author(s):  
Abdolrasol Rahimi ◽  
Hamed Hatami-Marbini
Keyword(s):  
Tensile Properties ◽  
Dermatan Sulfate ◽  
Lattice Structure ◽  
Corneal Thickness ◽  
Corneal Stroma ◽  
Swelling Pressure ◽  
Keratan Sulfate ◽  
Empty Space ◽  
Collagen Fibrils ◽  
Healthy Human

The mechanical behavior of the cornea is mainly governed by the microstructure and composition of the stroma. The stroma is a highly ordered extracellular matrix and constitutes about 90% of the corneal thickness. From the mechanics point of view, the corneal stroma can be considered as a polyelectrolyte gel which is composed of collagen fibrils embedded in an aqueous matrix. The collagen fibrils compose about 70% of cornea’s dry mass and are arranged in a regular lattice structure [2]. Previous studies have shown that while the collagen fibrils are primarily located parallel to the surface, they are not distributed uniformly in all directions and their preferred orientation is not same in different species. For example, collagen fibrils are almost equally distributed in the nasal-temporal and inferior-superior directions in healthy human corneas [4] and they are mainly aligned in the inferior-superior direction in bovine corneas[2]. The differences in the orientations of the collagen fibrils have seen to have important implications on the mechanical properties of the cornea. In addition to this observation, the relative distance between the collagen fibrils is expected to play a role in defining the mechanics of the tissue. It is well-documented that the proteoglycans bind collagen fibrils at regular sites and control their relative position. The main proteoglycan in the corneal stroma is decorin. Decorin is the simplest small leucine-rich proteoglycan with a single glycosaminoglycan side chain. Chondroitin sulfate, dermatan sulfate, and keratan sulfate are among the prevalent glycosaminoglycans found in the cornea. Under physiological conditions, these linear carbohydrate polymers are ionized and carry negative charges. Therefore, a hydrated gel is formed in the empty space between collagen fibrils by attracting water. It is known that the interaction of these negatively charged glycosaminoglycans with themselves and with the free ions contribute to the corneal swelling pressure and subsequently to its compressive stiffness. Nevertheless, their possible influence on the corneal tensile properties is yet to be determined. In this work, we experimentally characterized the tensile properties of the bovine corneal stroma in different bathing solutions. Furthermore, a quasi-linear viscoelastic (QLV) model was used to examine the effect of bathing fluids and corneal hydration on mechanical parameter of the cornea.

scholarly journals A cornealis sebgyógyulás és az extracelluláris mátrix

2016 ◽  
Vol 157 (25) ◽  
pp. 995-999
Author(s):  
Gréta Varkoly ◽  
János Bencze ◽  
Tibor Hortobágyi ◽  
László Módis
Keyword(s):  
Extracellular Matrix ◽  
Growth Factors ◽  
Dermatan Sulfate ◽  
Keratan Sulfate ◽  
Scar Tissue ◽  
Collagen Fibrils ◽  
Proteoglycan Synthesis ◽  
Abnormal Structure ◽  
Fibrillar Collagens ◽  
Corneal Scar

The cornea is the first refractive element of the eye. The transparency of the cornea results from the regularly arranged collagen fibrils, forming lamellar structure and the leucin rich proteoglycans, which make interactions between the fibrils. The adult cornea consists mainly of fibril-forming collagens. The cornea has less amount of fibril associated and non-fibrillar collagens. The main proteoglycans of the cornea are keratan-sulfate proteoglycans and it also contains dermatan-sulfate proteoglycans. Disorders of the proteoglycan synthesis lead to the disruption of the unique pattern and result in thicker collagen fibrils. The abnormal structure of the extracellular matrix can generate corneal disorders and the loss of corneal transparency. Furthermore, proteoglycans and collagens have an important role in wound healing. In injury the keratocytes produce higher amounts of collagens and proteoglycans mediated by growth factors. Depending on the ratio of the cells and growth factors the extracellular matrix returns to normal or corneal scar tissue develops. Orv. Hetil., 2016, 157(25), 995–999.

Type VI Collagen Is Associated with Collagen Fibrils Through Chondroitin??? Dermatan Sulfate Glycosaminoglycan in Mouse Corneal Stroma

1997 ◽  
Vol 37 (1) ◽  
pp. 174
Author(s):  
S Kimura ◽  
M Nakasmura ◽  
M Kobayashi ◽  
K Hirano ◽  
T Hoshino ◽  
...  
Keyword(s):  
Dermatan Sulfate ◽  
Corneal Stroma ◽  
Collagen Fibrils ◽  
Type Vi Collagen
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