On Mechanics of Connective Tissue: Assessing the Electrostatic Contribution to Corneal Stroma Elasticity

2009 ◽  
Vol 1239 ◽  
Author(s):  
Hamed Hatami-Marbini ◽  
Peter M. Pinsky
Keyword(s):  
Corneal Stroma ◽  
Unit Cell ◽  
Tissue Elasticity ◽  
The Finite Element Method ◽  
Connective Tissues ◽  
Electrostatic Contribution ◽  
Hexagonal Arrangement ◽  
Collagenous Tissues ◽  
Hierarchal Structure ◽  
And Cartilage

AbstractThe extracellular matrix plays a crucial role in defining the mechanical properties of connective tissues like cornea, heart, tendon, bone and cartilage among many others. The unique properties of these collagenous tissues arise because of both the hierarchal structure of collagens and the presence of negatively charged proteoglycans (PGs) which hold collagen fibers together. Here, in an effort to understand the mechanics of these structures, using the nonlinear Poison-Boltzmann (PB) equation, we study the electrostatic contribution to the elasticity of corneal stroma due to the presence of negatively charged PG glycosminoglycans (GAGs). Since collagens and GAGs have a regular hexagonal arrangement inside the corneal stroma, a triangular unit cell is chosen. The finite element method is used to solve the PB equation inside this domain and to obtain the electric potential and ionic distributions. Having the ion and potential distributions throughout the unit cell, the electrostatic free energy is computed and the tissue elasticity is calculated using the energy method. It is shown that as the ionic bath concentration increases; the electrostatic contribution to tissue elasticity is reduced.

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.

The Contribution of Proteoglycans on the Mechanical Properties of the Corneal Stroma

2010 ◽  
Author(s):  
Hamed Hatami-Marbini ◽  
Peter M. Pinsky
Keyword(s):  
Elastic Moduli ◽  
Core Protein ◽  
Electrical Potential ◽  
Corneal Stroma ◽  
Unit Cell ◽  
Side Chain ◽  
Ion Distribution ◽  
Electrostatic Contribution ◽  
Poisson Boltzmann ◽  
Ph Conditions

This paper studies the electrostatic contribution to the elasticity of corneal stroma using the Poisson-Boltzmann (PB) equation. Corneal stroma is a transparent connective tissue consisting of regularly organized collagen fibrils and proteoglycans (PGs) within an aqueous matrix. The cornea proteoglycan decorin is crucial for the regulation of collagen fibril diameters and their spacings. Decorin is the simplest small leucine-rich PG and is made up of a core protein and a glycosaminoglycan (GAG) side chain. Under physiological pH conditions, GAG molecules are completely ionized and become negatively charged. Their repulsive electrostatic interaction, mediated by free ions inside the bath, controls collagen interfibril spacings and contributes to corneal stiffness. In order to quantify the electrostatic contribution of GAGs to the elastic properties of the cornea, we define a unit cell in which GAGs are represented as cylindrical rods with a fixed charge density. The unit cell is deformed affinely and the electrical potential and free ion distribution inside the unit cell are obtained from the solution of the nonlinear PB equation. Having the potential and charge distribution, the changes in electrostatic free energy due to the deformation gives the electrostatic elastic moduli.

scholarly journals Apoptosis in the Extraosseous Calcification Process

Cells ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 131
Author(s):  
Federica Boraldi ◽  
Francesco Demetrio Lofaro ◽  
Daniela Quaglino
Keyword(s):  
Genetic Basis ◽  
Membrane Vesicles ◽  
Matrix Vesicles ◽  
Apoptotic Bodies ◽  
Connective Tissues ◽  
Mineralization Process ◽  
Mitochondrial Alterations ◽  
Age Related ◽  
And Oxidative Stress ◽  
And Cartilage

Extraosseous calcification is a pathologic mineralization process occurring in soft connective tissues (e.g., skin, vessels, tendons, and cartilage). It can take place on a genetic basis or as a consequence of acquired chronic diseases. In this last case, the etiology is multifactorial, including both extra- and intracellular mechanisms, such as the formation of membrane vesicles (e.g., matrix vesicles and apoptotic bodies), mitochondrial alterations, and oxidative stress. This review is an overview of extraosseous calcification mechanisms focusing on the relationships between apoptosis and mineralization in cartilage and vascular tissues, as these are the two tissues mostly affected by a number of age-related diseases having a progressively increased impact in Western Countries.

Stress Dependent Collagen Fibril Diameter Distribution in Human Aortic Valves

2007 ◽  
Author(s):  
Angelique Balguid ◽  
Anita Mol ◽  
Niels Driessen ◽  
Carlijn Bouten ◽  
Frank Baaijens
Keyword(s):  
Mechanical Properties ◽  
Collagen Fibril ◽  
Diameter Distribution ◽  
Connective Tissues ◽  
Aortic Valves ◽  
Cross Links ◽  
Fibril Morphology ◽  
Stress Dependent ◽  
Collagenous Tissues ◽  
Fibril Diameter

The mechanical properties of collagenous tissues are known to depend on a wide variety of factors, such as the type of tissue and the composition of its extracellular matrix. Relating mechanical roles to individual matrix components in such a complex system is difficult, if not impossible. However, as collagen is the main load bearing component in connective tissues, the relation between collagen and tissue biomechanics has been studied extensively in various types of tissues. The type of collagen, the amount and type of inter- and intramolecular covalent cross-links and collagen fibril morphology are involved in the tissues mechanical behavior (Beekman et al., 1997; Parry et al., 1978; Avery and Bailey, 2005). From literature it is known that the the collagen fibril diameter distribution can be directly related to the mechanical properties of the tissue. In particular, the diameter distribution of collagen fibrils is largely determined by the tissues requirement for tensile strength and elasticity (Parry et al., 1978).

Finite Deformation Behavior of Biological Soft Material on Cartilage Anisotropy under Loading Conditions

2006 ◽  
Vol 111 ◽  
pp. 127-130
Author(s):  
Boonyong Punantapong ◽  
Somchai Thongtem ◽  
M.J. Fagan ◽  
C. Soorapanth
Keyword(s):  
Deformation Behavior ◽  
Cartilage Degeneration ◽  
Biomechanical Properties ◽  
Pericellular Matrix ◽  
The Finite Element Method ◽  
Confined Compression ◽  
Connective Tissues ◽  
Cartilage Surface ◽  
Fluid Content ◽  
Glenoid Surface

Cartilage and bone are specialized connective tissues composed of roughly the same material: cell embedded in an extracellular matrix, permeated by the network of fibers. Then the properties of cartilage are anisotropic and inhomogeneous structure. At the same time, the structure of cartilage is rather porous allowing fluid to move in and out of the tissue. Thus the properties of cartilage were changed with the fluid content. The objective of this study is to demonstrate that the biomechanical properties of the pericellular matrix vary with depth from the coated cartilage surface, and observed regions of cartilage failure. This objective is achieved by solving problems with the finite element method. The conceptual model was subjected to the boundary conditions of confined compression on porous of cartilage anisotropy. The experimental results were demonstrated that neither the Young’s modulus nor the Poisson’s ratios exhibit the same values when measured along the loading directions. The results were supported an essential functional property of the tissue which the glenoid surface may be susceptible to cartilage degeneration.

scholarly journals Dual scaled approach SPR-based PCF RI sensor with ultra-low loss

2021 ◽  
Vol 2070 (1) ◽  
pp. 012109
Author(s):  
Samiha Nuzhat ◽  
Sanjida Sultana ◽  
Faiyaz Bin Hassan ◽  
Shovasis Kumar Biswas ◽  
Mohona Das Gupta ◽  
...  
Keyword(s):  
Figure Of Merit ◽  
Hexagonal Lattice ◽  
Confinement Loss ◽  
The Finite Element Method ◽  
Low Loss ◽  
Plasmonic Material ◽  
Crystal Fiber ◽  
Spr Sensor ◽  
Wavelength Sensitivity ◽  
Hexagonal Arrangement

Abstract We demonstrate an ultra-low loss photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR)in this paper. In this refractive index (RI) sensor, we explored hexagonal-arrangement of airholes and employed only two different sizes of it. The formation of airholes makes the confinement loss (CL) surprisingly low. The maximum CL is as low as 10.71 and 28.58 dB/cm for x and y-pol modes, respectively within a range of refractive indices 1.33-1.40. The maximum gained amplitude sensitivity is -1212 RIU−1 and -2430 RIU−1, and the maximum figure of merit is as high as 583 and 467 respectively for x and y-polarization (pol) modes respectively. In addition to that, we got a maximum wavelength sensitivity, Sw of 14,000nm/RIU for both x and y-pol modes with a minimum sensor resolution of 7.143x10−6. Gold is preferred over other materials as the plasmonic material for its inert behaviour and higher chemical stability. The analysis was carried out using the finite element method (FEM). This sensor, with its elegant configuration, fabrication feasibility, ultra-low loss, stands out to be an effective and eminent prospect in the current burgeoning SPR sensor realm and also prompts further creative exploration in its hexagonal lattice arrangements.

scholarly journals STEADY STATE FINITE ELEMENT ANALYSIS OF A SINGLE STACK COLD PLATE WITH HEAT LOSSES

2017 ◽  
Vol 19 (1) ◽  
pp. 77-90 ◽  
Author(s):  
G. A. Quadir ◽  
Shiao Lin Bell ◽  
K. N. Seetharamu ◽  
A. Y. Hassan
Keyword(s):  
Finite Element ◽  
Steady State ◽  
Single Unit ◽  
Heat Losses ◽  
Unit Cell ◽  
Bottom Surface ◽  
Cold Plate ◽  
The Finite Element Method ◽  
Element Analysis ◽  
Unit Cells

Steady state analysis of a single stack cold plate used for the cooling of electronic components is carried out using the finite element method. The present methodology takes into account the heat losses from the top and bottom surfaces of the stack. In addition dimensionless parameters are used in the analysis. The analysis is divided into two parts: a single unit cell analysis and the analysis of the assembly of several unit cells. The results from the present analysis of a single unit cell for single stack cold plate without heat losses compare well with those available in the literature. The analyses of the assembly of unit cells with heat losses from the top and bottom surface of the stack show that the single unit cell can be considered to be the representative of the stacks only when there are no heat losses.

A Variational Asymptotic Model for Predicting Initial Yielding Surface and Elastoplastic Behavior of Metal Matrix Composite Materials

2007 ◽  
Author(s):  
Tian Tang ◽  
Wenbin Yu
Keyword(s):  
Metal Matrix ◽  
Energy Functional ◽  
Unit Cell ◽  
Asymptotic Model ◽  
Matrix Composites ◽  
The Finite Element Method ◽  
Elastoplastic Behavior ◽  
Variational Asymptotic ◽  
Variational Asymptotic Method ◽  
Variational Statement

The focus of this paper is to develop a micromechanics model based on the variational asymptotic method for unit cell homogenization (VAMUCH) for predicting of the initial yielding surface, overall instantaneous moduli, and elastoplastic behavior of metal matrix composites. Considering the size of the microstructure as a small parameter, we can formulate a variational statement of the unit cell through an asymptotic expansion of the energy functional. To handle realistic microstructures, we implement this new model using the finite element method. For model validation, we used a few examples to demonstrate the application and accuracy of this theory and the companion code.

The Kinetics of Chemically Induced Nonequilibrium Swelling of Articular Cartilage and Corneal Stroma

1987 ◽  
Vol 109 (1) ◽  
pp. 79-89 ◽  
Author(s):  
S. R. Eisenberg ◽  
A. J. Grodzinsky
Keyword(s):  
Articular Cartilage ◽  
Tissue Sample ◽  
Constitutive Relations ◽  
Corneal Stroma ◽  
Chemical Diffusion ◽  
Connective Tissues ◽  
Bovine Articular Cartilage ◽  
Fluid Redistribution ◽  
Chemically Induced ◽  
Kinetics Of

An electromechanical model for charged, hydrated tissues is developed to predict the kinetics of changes in swelling and isometric compressive stress induced by changes in bath salt concentration. The model focuses on ionic transport as the rate limiting step in chemically modulating electrical interactions between the charged macromolecules of the extracellular matrix. The swelling response to such changes in local interaction forces is determined by the relative rates of chemical diffusion and fluid redistribution in the tissue sample. We have tested the model by comparing the experimentally observed salt-induced stress relaxation response in bovine articular cartilage and corneal stroma to the response predicted by the model using constitutive relations for the concentration dependent material properties of the tissues reported in a related study. The qualitatively good agreement between our experimental measurements and the predictions of the model supports the physical basis of the model and demonstrates the model’s ability to discriminate between the two soft connective tissues that were examined.

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