Constitutive Modeling of Corneal Tissue: Influence of Three-Dimensional Collagen Fiber Microstructure

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Shuolun Wang ◽  
Hamed Hatami-Marbini
Keyword(s):  
Extracellular Matrix ◽  
Constitutive Modeling ◽  
Mechanical Response ◽  
Thickness Distribution ◽  
Three Dimensional ◽  
Vital Role ◽  
Collagen Fibrils ◽  
Model Parameters ◽  
Corneal Tissue ◽  
Numerical Predictions

Abstract The cornea, the transparent tissue in the front of the eye, along with the sclera, plays a vital role in protecting the inner structures of the eyeball. The precise shape and mechanical strength of this tissue are mostly determined by the unique microstructure of its extracellular matrix. A clear picture of the 3D arrangement of collagen fibrils within the corneal extracellular matrix has recently been obtained from the secondary harmonic generation images. However, this important information about the through-thickness distribution of collagen fibrils was seldom taken into account in the constitutive modeling of the corneal behavior. This work creates a generalized structure tensor (GST) model to investigate the mechanical influence of collagen fibril through-thickness distribution. It then uses numerical simulations of the corneal mechanical response in inflation experiments to assess the efficacy of the proposed model. A parametric study is also done to investigate the influence of model parameters on numerical predictions. Finally, a brief comparison between the performance of this new constitutive model and a recent angular integration (AI) model from the literature is given.

Zonal Poisson Effect on the Chondron Deformation in Articular Cartilage under Compression

2007 ◽  
Vol 342-343 ◽  
pp. 133-136
Author(s):  
Jae Bong Choi
Keyword(s):  
Extracellular Matrix ◽  
Articular Cartilage ◽  
Mechanical Response ◽  
Three Dimensional ◽  
Pericellular Matrix ◽  
Poisson Effect ◽  
Type Vi Collagen ◽  
Confocal Images ◽  
Three Dimensional Models

The objective of this study was to quantify the zonal difference of the in situ chondron’s Poisson effect under different magnitudes of compression. Fluorescence immunolabeling for type VI collagen was used to identify the pericellular matrix (PCM) and chondron, and a series of fluorescent confocal images were recorded and reconstructed to form quantitative three-dimensional models. The zonal variations in the mechanical response of the chondron do not appear to be due to zonal differences in PCM properties, but rather seem to result from significant inhomogeneities in relative stiffnesses of the extracellular matrix (ECM) and PCM with depth.

Parameters Affecting the Local Buckling Response of High Strength Linepipe

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Ali Fatemi ◽  
Shawn Kenny
Keyword(s):  
Yield Strength ◽  
Large Scale ◽  
Mechanical Response ◽  
Local Buckling ◽  
High Strength ◽  
Combined Loading ◽  
Parameter Study ◽  
Model Parameters ◽  
Pipe Length ◽  
Numerical Predictions

The local buckling response and post-buckling mechanical performance of high strength linepipe subject to combined loading state was evaluated using the finite element (FE) simulator abaqus/standard v6.12. The constitutive model parameters were established through laboratory tests and the numerical modeling procedures were verified with large-scale experiments investigating the local buckling response of high strength linepipe. The numerical predictions demonstrated a high level of consistency and correspondence with the measured experimental behavior with respect to the peak moment, strain capacity, deformation mechanism, and local buckling response well into the postyield range. A parametric study on the local buckling response of high strength plain and girth weld pipelines was conducted. The loading conditions included internal pressure and end rotation. The pipe mechanical response parameters examined included moment–curvature, ovalization, local strain, and modal response. The magnitude and distribution of the characteristic geometric imperfections and the end constraint, associated with the boundary conditions and pipe length, had a significant influence on the predicted local buckling response. The importance of material parameters on the local buckling response, including the yield strength (YS), yield strength to tensile strength ratio (Y/T), and anisotropy, was also established through the numerical parameter study. For girth weld linepipe, the study demonstrated the importance of the local high/low misalignment, associated with the circumferential girth weld, on the local buckling response.

scholarly journals Glassy dynamics in three-dimensional embryonic tissues

2013 ◽  
Vol 10 (89) ◽  
pp. 20130726 ◽  
Author(s):  
Eva-Maria Schötz ◽  
Marcos Lanio ◽  
Jared A. Talbot ◽  
M. Lisa Manning
Keyword(s):  
Pattern Formation ◽  
Mechanical Response ◽  
Three Dimensional ◽  
Biological Tissues ◽  
Model Parameters ◽  
Elastic Solids ◽  
Cell Dynamics ◽  
Cell Parameters ◽  
Embryonic Tissues ◽  
Long Timescales

Many biological tissues are viscoelastic, behaving as elastic solids on short timescales and fluids on long timescales. This collective mechanical behaviour enables and helps to guide pattern formation and tissue layering. Here, we investigate the mechanical properties of three-dimensional tissue explants from zebrafish embryos by analysing individual cell tracks and macroscopic mechanical response. We find that the cell dynamics inside the tissue exhibit features of supercooled fluids, including subdiffusive trajectories and signatures of caging behaviour. We develop a minimal, three-parameter mechanical model for these dynamics, which we calibrate using only information about cell tracks. This model generates predictions about the macroscopic bulk response of the tissue (with no fit parameters) that are verified experimentally, providing a strong validation of the model. The best-fit model parameters indicate that although the tissue is fluid-like, it is close to a glass transition, suggesting that small changes to single-cell parameters could generate a significant change in the viscoelastic properties of the tissue. These results provide a robust framework for quantifying and modelling mechanically driven pattern formation in tissues.

An Analytic Model for PTH/PWB Stress Due to Three-Dimensional Forces Generated by Symmetric Compliant-Pins

2007 ◽  
Author(s):  
S. Roettele ◽  
A. Dasgupta
Keyword(s):  
Rapid Assessment ◽  
Three Dimensional ◽  
Design Guidelines ◽  
Contact Forces ◽  
Analytical Models ◽  
Model Parameters ◽  
Axial Forces ◽  
Numerical Predictions ◽  
Pin Geometry ◽  
Insertion Process

Analytical models are presented, to address the deformations and stresses caused in PWBs by compliant-pins used for solder-less component-interconnection technologies. These models are proposed for rapid-assessment capabilities when designing such interconnect assemblies for reliability. This model is based on mechanistic understanding of the physics of the pin insertion process. Previous studies in the literature focused on analytic solutions for the in-plane (radial and tangential) forces generated in the PWB & PTH due to the compliant-pin. In this study, the approach is extended to three-dimensional solutions by approximately including the axial forces generated by friction during the compliant-pin insertion process. The solution is linear elastic and is based on Fourier series expansions of the contact forces generated by the compliant-pin. This approximate solution therefore is appropriate for rapid-assessment capabilities for parametric trade-off studies and design guidelines. Model parameters include PWB hole-diameter, PTH plating thickness, and the PTH and PWB material properties. The model can be used with any mirror-symmetric compliant-pin geometry and stiffness. The numerical predictions allow us to quantify the dependence of the stresses in the PWB on compliant-pin geometry and on the PTH construction.

scholarly journals Alignment hierarchies: engineering architecture from the nanometre to the micrometre scale

2010 ◽  
Vol 7 (suppl_6) ◽  
Author(s):  
Alvena Kureshi ◽  
Umber Cheema ◽  
Tijna Alekseeva ◽  
Alison Cambrey ◽  
Robert Brown
Keyword(s):  
Extracellular Matrix ◽  
Fluid Flow ◽  
Three Dimensional ◽  
Collagen Scaffold ◽  
Collagen Fibrils ◽  
Dimensional Structure ◽  
Protein Diffusion ◽  
Collagen Gels ◽  
Protein Factor ◽  
Extracellular Matrix Components

Natural tissues are built of metabolites, soluble proteins and solid extracellular matrix components (largely fibrils) together with cells. These are configured in highly organized hierarchies of structure across length scales from nanometre to millimetre, with alignments that are dominated by anisotropies in their fibrillar matrix. If we are to successfully engineer tissues, these hierarchies need to be mimicked with an understanding of the interaction between them. In particular, the movement of different elements of the tissue (e.g. molecules, cells and bulk fluids) is controlled by matrix structures at distinct scales. We present three novel systems to introduce alignment of collagen fibrils, cells and growth factor gradients within a three-dimensional collagen scaffold using fluid flow, embossing and layering of construct. Importantly, these can be seen as different parts of the same hierarchy of three-dimensional structure, as they are all formed into dense collagen gels. Fluid flow aligns collagen fibrils at the nanoscale, embossed topographical features provide alignment cues at the microscale and introducing layered configuration to three-dimensional collagen scaffolds provides microscale- and mesoscale-aligned pathways for protein factor delivery as well as barriers to confine protein diffusion to specific spatial directions. These seemingly separate methods can be employed to increase complexity of simple extracellular matrix scaffolds, providing insight into new approaches to directly fabricate complex physical and chemical cues at different hierarchical scales, similar to those in natural tissues.

scholarly journals The release of surface-anchored α-tectorin, an apical extracellular matrix protein, mediates tectorial membrane organization

2019 ◽  
Vol 5 (11) ◽  
pp. eaay6300 ◽  
Author(s):  
Dong-Kyu Kim ◽  
Ju Ang Kim ◽  
Joosang Park ◽  
Ava Niazi ◽  
Ali Almishaal ◽  
...  
Keyword(s):  
Extracellular Matrix ◽  
Matrix Protein ◽  
Three Dimensional ◽  
Multilayered Structure ◽  
Sensory Epithelium ◽  
Collagen Fibrils ◽  
Extracellular Matrix Protein ◽  
Tectorial Membrane ◽  
Epithelial Surface ◽  
Three Dimensional Printing

The tectorial membrane (TM) is an apical extracellular matrix (ECM) that hovers over the cochlear sensory epithelium and plays an essential role in auditory transduction. The TM forms facing the luminal endolymph-filled space and exhibits complex ultrastructure. Contrary to the current extracellular assembly model, which posits that secreted collagen fibrils and ECM components self-arrange in the extracellular space, we show that surface tethering of α-tectorin (TECTA) via a glycosylphosphatidylinositol anchor is essential to prevent diffusion of secreted TM components. In the absence of surface-tethered TECTA, collagen fibrils aggregate randomly and fail to recruit TM glycoproteins. Conversely, conversion of TECTA into a transmembrane form results in a layer of collagens on the epithelial surface that fails to form a multilayered structure. We propose a three-dimensional printing model for TM morphogenesis: A new layer of ECM is printed on the cell surface concomitant with the release of a preestablished layer to generate the multilayered TM.

Numerical performance assessment of buried corrugated metal culvert subject to service load conditions

2020 ◽  
pp. 1-16
Author(s):  
Elham Nakhostin ◽  
Shawn Kenny ◽  
Siva Sivathayalan
Keyword(s):  
Computational Models ◽  
Load Transfer ◽  
Mechanical Response ◽  
Three Dimensional ◽  
Local Variation ◽  
Third Party ◽  
Nonlinear Behaviour ◽  
Numerical Predictions ◽  
Service Load ◽  
Load Conditions

Two- and three-dimensional continuum finite element methods were used to assess the mechanical response of buried metal culverts subjected to service load conditions. The analysis explored the influence of the culvert profile, cover depth, section aspect ratio, and service load magnitude on culvert deformation, thrust, and section moment response. The numerical predictions were calibrated using third-party experimental data. For shallow burial conditions, the culvert section profile was found to be an influential parameter on the predicted culvert response where the soil–culvert interaction mechanisms and load transfer processes are governed by nonlinear behaviour. Models that incorporate the corrugated culvert profile provided better estimates of the culvert thrust than the simplified computational models that are typically used in analysis. Results from this study demonstrate that existing simplified methods cannot capture the local variation (i.e., amplitude, waveform) of the membrane strain and section thrust particularly between the crest and trough of corrugation.

scholarly journals A microstructural model of cross-link interaction between collagen fibrils in the human cornea

2019 ◽  
Vol 377 (2144) ◽  
pp. 20180079 ◽  
Author(s):  
A. Pandolfi ◽  
A. Gizzi ◽  
M. Vasta
Keyword(s):  
Mechanical Response ◽  
Applied Mathematics ◽  
Micromechanical Model ◽  
Collagen Fibrils ◽  
Structural Function ◽  
Human Cornea ◽  
Corneal Tissue ◽  
Cross Link ◽  
Stromal Tissue ◽  
Microstructural Model

We propose a simplified micromechanical model of the fibrous reinforcement of the corneal tissue. We restrict our consideration to the structural function of the collagen fibrils located in the stroma and disregard the other all-important components of the cornea. The reinforcing structure is modelled with two sets of parallel fibrils, connected by transversal bonds within the single fibril family (inter-cross-link) and across the two families (intra-cross-link). The particular design chosen for this ideal structure relies on the fact that its ability to sustain loads is dependent on the degree of the cross-link and, therefore, on the density and stiffness of the bonds. We analyse the mechanical response of the system according to the type of interlacing and on the stiffness of fibres and bonds. Results show that the weakening of transversal bonds is associated with a marked increase of the deformability of the system. In particular, the deterioration of transversal bonds due to mechanical, chemical or enzymatic reasons can justify the loss of stiffness of the stromal tissue resulting in localized thinning and bulging typically observed in keratoconus corneas. This article is part of the theme issue ‘Rivlin's legacy in continuum mechanics and applied mathematics’.

scholarly journals Numerical Simulations of Components Produced by Fused Deposition 3D Printing

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4625
Author(s):  
Martina Scapin ◽  
Lorenzo Peroni
Keyword(s):  
Mechanical Properties ◽  
Fused Deposition Modeling ◽  
Mechanical Response ◽  
Three Dimensional ◽  
Transversely Isotropic ◽  
Material Model ◽  
Model Parameters ◽  
Fused Deposition ◽  
Four Point Bending ◽  
Dog Bone

Three-dimensional printing technology using fused deposition modeling processes is becoming more and more widespread thanks to the improvements in the mechanical properties of materials with the addition of short fibers into the polymeric filaments. The final mechanical properties of the printed components depend, not only on the properties of the filament, but also on several printing parameters. The main purpose of this study was the development of a tool for designers to predict the real mechanical properties of printed components by performing finite element analyses. Two different materials (nylon reinforced with glass or carbon fibers) were investigated. The experimental identification of the elastic material model parameters was performed by testing printed fully filled dog bone specimens in two different directions. The obtained parameters were used in numerical analyses to predict the mechanical response of simple structures. Blocks of 20 mm × 20 mm × 160 mm were printed in four different percentages of a triangular infill pattern. Experimental and numerical four-point bending tests were performed, and the results were compared in terms of load versus curvature. The analysis of the results demonstrated that the purely elastic transversely isotropic material model is adequate for predicting behavior, at least before nonlinearities occur.

Construction of plastic contact deformation maps on ceramics: a case study on aluminum nitride

1996 ◽  
Vol 54 ◽  
pp. 636-637
Author(s):  
D. L. Callahan
Keyword(s):  
Plastic Deformation ◽  
Aluminum Nitride ◽  
Mechanical Response ◽  
Three Dimensional ◽  
Bright Field Image ◽  
Perfectly Plastic ◽  
Contrast Analysis ◽  
Deformation Patterns

Modern polishing, precision machining and microindentation techniques allow the processing and mechanical characterization of ceramics at nanometric scales and within entirely plastic deformation regimes. The mechanical response of most ceramics to such highly constrained contact is not predictable from macroscopic properties and the microstructural deformation patterns have proven difficult to characterize by the application of any individual technique. In this study, TEM techniques of contrast analysis and CBED are combined with stereographic analysis to construct a three-dimensional microstructure deformation map of the surface of a perfectly plastic microindentation on macroscopically brittle aluminum nitride.The bright field image in Figure 1 shows a lg Vickers microindentation contained within a single AlN grain far from any boundaries. High densities of dislocations are evident, particularly near facet edges but are not individually resolvable. The prominent bend contours also indicate the severity of plastic deformation. Figure 2 is a selected area diffraction pattern covering the entire indentation area.

Sign in / Sign up

Export Citation Format

Share Document