On Unconfined Compression Response of the Porcine Corneal Stroma

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.

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.

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.

A Transversely Isotropic Biphasic Model for Unconfined Compression of Growth Plate and Chondroepiphysis

1998 ◽  
Vol 120 (4) ◽  
pp. 491-496 ◽  
Author(s):  
B. Cohen ◽  
W. M. Lai ◽  
V. C. Mow
Keyword(s):  
Stress Relaxation ◽  
Growth Plate ◽  
Soft Tissues ◽  
Transverse Isotropy ◽  
Transversely Isotropic ◽  
Solid Matrix ◽  
Elastic Model ◽  
Unconfined Compression ◽  
Biphasic Model ◽  
Cylindrical Axis

Using the biphasic theory for hydrated soft tissues (Mow et al., 1980) and a transversely isotropic elastic model for the solid matrix, an analytical solution is presented for the unconfined compression of cylindrical disks of growth plate tissues compressed between two rigid platens with a frictionless interface. The axisymmetric case where the plane of transverse isotropy is perpendicular to the cylindrical axis is studied, and the stress-relaxation response to imposed step and ramp displacements is solved. This solution is then used to analyze experimental data from unconfined compression stress-relaxation tests performed on specimens from bovine distal ulnar growth plate and chondroepiphysis to determine the biphasic material parameters. The transversely isotropic biphasic model provides an excellent agreement between theory and experimental results, better than was previously achieved with an isotropic model, and can explain the observed experimental behavior in unconfined compression of these tissues.

Rapid Collagen-Directed Mineralization of Calcium Fluoride Nanocrystals with Periodically Patterned Nanostructure

Nanoscale ◽  
2021 ◽  
Author(s):  
Weijian Fang ◽  
Hang Ping ◽  
Wolfgang Wagermaier ◽  
Shenbao Jin ◽  
Shahrouz Amini ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Calcium Fluoride ◽  
Periodic Structures ◽  
Collagen Fibrils ◽  
Hydroxyapatite Nanocrystals

Collagen fibrils present periodic structures, which provide space for intrafibrillar growth of oriented hydroxyapatite nanocrystals in bone and contribute to the good mechanical properties of bone. However, there are not...

scholarly journals Evolution of Meniscal Biomechanical Properties with Growth: An Experimental and Numerical Study

2021 ◽  
Vol 8 (5) ◽  
pp. 70
Author(s):  
Marco Ferroni ◽  
Beatrice Belgio ◽  
Giuseppe M. Peretti ◽  
Alessia Di Giancamillo ◽  
Federica Boschetti
Keyword(s):  
Mechanical Properties ◽  
Stress Relaxation ◽  
Developmental Stage ◽  
Mechanical Response ◽  
Numerical Study ◽  
Numerical Models ◽  
Mechanical Stimulus ◽  
Specific Response ◽  
Mechanical Parameters ◽  
Biochemical Analyses

The menisci of the knee are complex fibro-cartilaginous tissues that play important roles in load bearing, shock absorption, joint lubrication, and stabilization. The objective of this study was to evaluate the interaction between the different meniscal tissue components (i.e., the solid matrix constituents and the fluid phase) and the mechanical response according to the developmental stage of the tissue. Menisci derived from partially and fully developed pigs were analyzed. We carried out biochemical analyses to quantify glycosaminoglycan (GAG) and DNA content according to the developmental stage. These values were related to tissue mechanical properties that were measured in vitro by performing compression and tension tests on meniscal specimens. Both compression and tension protocols consisted of multi-ramp stress–relaxation tests comprised of increasing strains followed by stress–relaxation to equilibrium. To better understand the mechanical response to different directions of mechanical stimulus and to relate it to the tissue structural composition and development, we performed numerical simulations that implemented different constitutive models (poro-elasticity, viscoelasticity, transversal isotropy, or combinations of the above) using the commercial software COMSOL Multiphysics. The numerical models also allowed us to determine several mechanical parameters that cannot be directly measured by experimental tests. The results of our investigation showed that the meniscus is a non-linear, anisotropic, non-homogeneous material: mechanical parameters increase with strain, depend on the direction of load, and vary among regions (anterior, central, and posterior). Preliminary numerical results showed the predominant role of the different tissue components depending on the mechanical stimulus. The outcomes of biochemical analyses related to mechanical properties confirmed the findings of the numerical models, suggesting a specific response of meniscal cells to the regional mechanical stimuli in the knee joint. During maturation, the increase in compressive moduli could be explained by cell differentiation from fibroblasts to metabolically active chondrocytes, as indicated by the found increase in GAG/DNA ratio. The changes of tensile mechanical response during development could be related to collagen II accumulation during growth. This study provides new information on the changes of tissue structural components during maturation and the relationship between tissue composition and mechanical response.

scholarly journals Combined effect of mineralogical and chemical parameters on swelling behaviour of expansive soils

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Bendadi Hanumantha Rao ◽  
Peddireddy Sreekanth Reddy ◽  
Bijayananda Mohanty ◽  
Krishna R. Reddy
Keyword(s):  
Expansive Soils ◽  
Research Work ◽  
Swelling Pressure ◽  
Combined Effect ◽  
Practical Significance ◽  
Chemical Compositions ◽  
Chemical Parameters ◽  
Swelling Behaviour ◽  
Mineral Contents ◽  
Swelling Properties

AbstractMicrolevel properties such as mineralogical and chemical compositions greatly control the macro behaviour of expansive soils. In this paper, the combined effect of mineral (i.e. montmorillonite, MMC) and chemical contents (i.e. Ca and Na in their total (T), leachable (L) and exchangeable form (CEC)) on swelling behaviour is investigated in a comprehensive way. Several 3-dimensional (3D) graphs correlating MMC and Ca/Na ratio, together, with swelling property (swelling potential, Sa, and swelling pressure, Sp) are developed. 3D plots, in general, portrayed a non-linear relationship of Sa and Sp with MMC and Ca/Na ratio, together. It is hypothesized that swelling initially is triggered by chemical parameters due to their quick and rapid ionization capability, but the overall swelling phenomenon is largely controlled by MMC. It is importantly found that expansive soils are dominant with divalent Ca++ ions up to MMC of 67% and beyond this percentage, monovalent Na+ ions are prevalent. From the interpretation of results, the maximum Sa of 18% and Sp of 93 kPa is measured at MMC of 43%, (Ca/Na)T of 10–14 and (Ca/Na)L of 2–7. It is concluded from study that total CEC + MMC for determining Sa and (Ca/Na)T + MMC for determining Sp are superior parameters to be considered. The findings of the study also excellently endorsed the results of Foster32, who stated that ionization of Na or Ca depends on the constituent mineral contents. The findings presented herein are unique, interesting and bear very practical significance, as no earlier research work reported such findings by accounting for chemical and mineralogical parameters impact, in tandem, on swelling properties.

scholarly journals Mechanical Properties of Bioengineered Corneal Stroma

2021 ◽  
pp. 2100972
Author(s):  
Nello Formisano ◽  
Cas Putten ◽  
Rhiannon Grant ◽  
Gozde Sahin ◽  
Roman K. Truckenmüller ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Corneal Stroma

Effect of Weld Line Formation on Morphology and Mechanical Properties for 3D-MID Technology

2015 ◽  
Vol 659 ◽  
pp. 659-665
Author(s):  
Supakit Chuaping ◽  
Thomas Mann ◽  
Rapeephun Dangtungee ◽  
Suchart Siengchin
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Flexural Strength ◽  
Injection Molding ◽  
Filler Content ◽  
Research Work ◽  
Weld Line ◽  
Processing Conditions ◽  
High Reduction ◽  
Flexural Tests

The topic of this research work was to demonstrate the feasibility of a 3D-MID concept using injection molding technique and investigate the effects of two weld line types on the structure and mechanical properties such as tensile, flexural strength and morphology. In order to obtain more understanding of the bonds between polymer and metals, two different polymer bases of polyphthalamide (PPA) with the same type and amount of filler content were produced by injection molding at the different processing conditions. A mold was designed in such a way that weld and meld line can be produced with different angles by changing as insert inside of the mold. The mechanical properties such as stiffness, tensile strength and flexural strength were determined in tensile and flexural tests, respectively. The results showed in line with the expectation of high reduction on mechanical properties in area where weld/meld lines occurred. The result of tensile test was clearly seen that weld and meld line showed a considerable influence on mechanical properties. The reduction in tensile strength was approximately 58% according to weld line types, whereas in flexural strength was approximately 62%. On the other hand, the effect of the injection times and mold temperatures on the tensile strength were marginal.

Transversely isotropic micromechanics model to determine effect of collagen fibre angle in mechanical properties of articular cartilage

2014 ◽  
Vol 29 (6) ◽  
pp. 377-383 ◽  
Author(s):  
S. Mohammad Mehdi Elhamian ◽  
M. Alizadeh ◽  
M. Mehrdad Shokrieh ◽  
A. Karimi ◽  
S. Pejman Madani
Keyword(s):  
Mechanical Properties ◽  
Articular Cartilage ◽  
Collagen Fibre ◽  
Transversely Isotropic ◽  
Micromechanics Model ◽  
Fibre Angle ◽  
Determine Effect
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