A Biphasic Model for Micro-Indentation of a Hydrogel-Based Contact Lens

The stiffness and hydraulic permeability of soft contact lenses may influence its clinical performance, e.g., on-eye movement, fitting, and wettability, and may be related to the occurrence of complications; e.g., lesions. It is therefore important to determine these properties in the design of comfortable contact lenses. Micro-indentation provides a nondestructive means of measuring mechanical properties of soft, hydrated contact lenses. However, certain geometrical and material considerations must be taken into account when analyzing output force-displacement (F-D) data. Rather than solely having a solid response, mechanical behavior of hydrogel contact lenses can be described as the coupled interaction between fluid transport through pores and solid matrix deformation. In addition, indentation of thin membranes (∼100μm) requires special consideration of boundary conditions at lens surfaces and at the indenter contact region. In this study, a biphasic finite element model was developed to simulate the micro-indentation of a hydrogel contact lens. The model accounts for a curved, thin hydrogel membrane supported on an impermeable mold. A time-varying boundary condition was implemented to model the contact interface between the impermeable spherical indenter and the lens. Parametric studies varying the indentation velocities and hydraulic permeability show F-D curves have a sensitive region outside of which the force response reaches asymptotic limits governed by either the solid matrix (slow indentation velocity, large permeability) or the fluid transport (high indentation velocity, low permeability). Using these results, biphasic properties (Young’s modulus and hydraulic permeability) were estimated by fitting model results to F-D curves obtained at multiple indentation velocities (1.2 and 20μm∕s). Fitting to micro-indentation tests of Etafilcon A resulted in an estimated permeability range of 1.0×10−15 to 5.0×10−15m4∕Ns and Young’s modulus range of 130to170kPa.

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Effect of the Quenching Temperature on the Phase Composition and Youngʹs Modulus of Corrosion-Resistant and Biocompatible Titanium Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.946.309 ◽

2019 ◽

Vol 946 ◽

pp. 309-314 ◽

Cited By ~ 1

Author(s):

Anatoly G. Illarionov ◽

S.V. Grib ◽

A.V. Huppeev

Keyword(s):

Phase Composition ◽

Titanium Alloys ◽

Young’S Modulus ◽

Young's Modulus ◽

Two Phase ◽

Quenching Temperature ◽

Thermo Calc Software ◽

Extreme Change ◽

The Relationship ◽

Micro Indentation

The relationship between the phase composition and the Young’s modulus in quenched PT-7M, Ti-6Al-7Nb, BT16 titanium alloys has been studied using the structural analysis, thermodynamic calculations in the Thermo-Calc software and micro-indentation. It is found that the nature of the change in the Young’s modulus in the investigated titanium alloys after quenching from the two-phase α+β-region depends on the chemical composition of the alloy, which determines the nature of the observed metastable phases (α', α", ω, β). The correlation between the extreme change in the Young’s modulus from the quenching temperature and the so-called interatomic bonding force (Fb) calculated from the electronic structure parameters of the α, α', β phases was shown for the Ti-6Al-7Nb alloy. The relationship between the limits of the Young’s modulus of the investigated alloys during quenching with the level of their alloying with α-and β-stabilizers is shown.

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Micromechanical Study of the Forged Ti-1023 Titanium Alloy by Micro-Indentation

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.765.160 ◽

2018 ◽

Vol 765 ◽

pp. 160-165

Author(s):

Jiang Li ◽

Fu Guo Li ◽

Xin Kai Ma ◽

Ming Jie Zhang ◽

Zhan Wei Yuan

Keyword(s):

Experimental Data ◽

Mechanical Properties ◽

Titanium Alloy ◽

Young’S Modulus ◽

Young's Modulus ◽

Strain Hardening Exponent ◽

Instrumental Approach ◽

Initial Yield Stress ◽

Non Destructive ◽

Micro Indentation

In order to study the micromechanical behaviour of the forged Ti-1023 titanium alloy, micro-indentation experiments of the forged Ti-1023 titanium alloy were performed with various maximum indentation loads from 500 mN to 4000 mN and various loading speeds from 5.06 mN/s to 51.85 mN/s. Using the experimental data, the non-destructive instrumental approach was applied to indicate the mechanical properties just like the Young’s modulusE, microhardnessH, initial yield stressσyand strain hardening exponentnusing theP-hcurves from the tests. The result showed that the value of the indentation Young’s modulus basically remain unchanged in the range from 110 GPa to 150 GPa andHdecreased with the increase of the load, the micro-indentaion plasticity constitutive equations were obtained by using Hookean elastic and power-law plastic stress-strain equations.

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Hydraulic permeability of granitic bedrock estimated from resistivity and young's modulus

10.1190/segj2018-084.1 ◽

2019 ◽

Author(s):

Sota Kawaguchi ◽

Tada-nori Goto

Keyword(s):

Young’S Modulus ◽

Young's Modulus ◽

Hydraulic Permeability

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Model for the Moisture Quenching of Solid-Matrix Phosphorescence via the Young's Modulus of Filter Paper

Applied Spectroscopy ◽

10.1366/0003702953963300 ◽

1995 ◽

Vol 49 (1) ◽

pp. 98-104 ◽

Cited By ~ 14

Author(s):

J. Chen ◽

Robert J. Hurtubise

Keyword(s):

Young’S Modulus ◽

Filter Paper ◽

Young's Modulus ◽

Solid Matrix

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Mechanical Characterization of Contact Lenses by Microindentation: Constant Velocity and Relaxation Testing

ASME 2008 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2008-192640 ◽

2008 ◽

Author(s):

Sung Jin Lee ◽

Gerald R. Bourne ◽

Xiaoming Chen ◽

W. Gregory Sawyer ◽

Malisa Sarntinoranont

Keyword(s):

Material Properties ◽

Fluid Transport ◽

Contact Lenses ◽

Solid Phase ◽

Clinical Performance ◽

Hydraulic Permeability ◽

Soft Contact Lenses ◽

Speed Up ◽

Design And Testing

Mechanical and fluid transport properties of soft contact lenses may influence clinical performance, e.g., on-eye movement, fitting, and wettability, and may be related to the occurrence of complications, e.g. lesions [1, 2]. In the mechanical assessment of soft hydrated materials, indentation is increasingly being used because of its nondestructive methods for testing these material properties allow for multiple tests to be performed on the same sample, which will speed up the design and testing process for hydrogel contact lenses. [3]. Contact lens hydrogels may be described as a biphasic material. The material properties governing biphasic behavior are the Young’s modulus of the solid phase, Poisson ratio’s, and hydraulic permeability which is measure of fluid conductance in porous media. Previous studies of indentation of biphasic media have been completed by Mow and coworkers [4]. Also, computational finite element (FE) models have also been developed [5].

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Experimental and Biphasic FEM Determinations of the Material Properties and Hydraulic Permeability of the Meniscus in Tension1

Journal of Biomechanical Engineering ◽

10.1115/1.1468868 ◽

2002 ◽

Vol 124 (3) ◽

pp. 315-321 ◽

Cited By ~ 84

Author(s):

Michelle A. LeRoux ◽

Lori A. Setton

Keyword(s):

Finite Element ◽

Stress Relaxation ◽

Transversely Isotropic ◽

Element Model ◽

Tensile Tests ◽

Solid Matrix ◽

Hydraulic Permeability ◽

Permeability Coefficients ◽

Matrix Properties ◽

Biphasic Finite Element

Tensile tests and biphasic finite element modeling were used to determine a set of transversely isotropic properties for the meniscus, including the hydraulic permeability coefficients and solid matrix properties. Stress-relaxation tests were conducted on planar samples of canine meniscus samples of different orientations, and the solid matrix properties were determined from equilibrium data. A 3-D linear biphasic and tranversely isotropic finite element model was developed to model the stress-relaxation behavior of the samples in tension, and optimization was used to determine the permeability coefficients, k1 and k2, governing fluid flow parallel and perpendicular to the collagen fibers, respectively. The collagen fibrillar orientation was observed to have an effect on the Young’s moduli (E1=67.8MPa,E2=11.1MPa) and Poisson’s ratios (ν12=2.13,ν21=1.50,ν23=1.02). However, a significant effect of anisotropy on permeability was not detected (k1=0.09×10−16m4/Ns,k2=0.10×10−16m4/Ns). The low permeability values determined in this study provide insight into the extent of fluid pressurization in the meniscus and will impact modeling predictions of load support in the meniscus.

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