Equivalent Mixed “PHETS” and “MPHETS” Poroelasttc-Transport-Swelling Finite Element Models for Soft Biological Tissues

1999 ◽  
Author(s):  
B. R. Simon ◽  
S. K. Williams ◽  
J. Liu ◽  
J. W. Nichol ◽  
P. H. Rigby ◽  
...  
Keyword(s):  
Finite Element ◽  
Chemical Potential ◽  
Biological Tissues ◽  
Finite Element Models ◽  
Material Interfaces ◽  
Soft Biological Tissues ◽  
Fibrous Matrix ◽  
Charged Species ◽  
Pressure Fields ◽  
Swelling Model

Abstract A soft hydrated tissue structure can be viewed as a “PETS” (poroelastic-transport-swelling) model, i.e., as a continuum composed of an incompressible porous solid (fibrous matrix with fixed charge density, FCD) that is saturated by a mobile incompressible fluid (water) containing mobile positively (p) and negatively (m) charged species. Previously, we described two PETS models — a “semi-mixed” porohyperelastic PHETS model (Simon et al. 1998) and a “fully mixed” MPHETS model (Simon et al. 1999) using FEMs (finite element models) that included geometric and material nonlinearity and coupled electrical/chemical/mechanical transport of the fluid and charged species. Here, we demonstrate the equivalence of the PHETS and MPHETS formulations that are useful when the solid and fluid materials are incompressible and the electrical-chemical potential and mechanical-osmotic pressure fields are discontinuous at material interfaces.

scholarly journals Tissue material properties and computational modelling of the human knee: A critical review

2017 ◽  
Author(s):  
Abby E Peters ◽  
Riaz Akhtar ◽  
Eithne J Comerford ◽  
Karl T Bates
Keyword(s):  
Systematic Review ◽  
Finite Element ◽  
Knee Joint ◽  
Mechanical Behaviour ◽  
Material Properties ◽  
Computational Modelling ◽  
Biological Tissues ◽  
Finite Element Models ◽  
Human Knee ◽  
Tissue Material

Understanding how structural and functional alterations of individual tissues impact on whole-joint function is challenging, particularly in humans where direct invasive experimentation is difficult. Finite element computational models produce quantitative predictions of the mechanical and physiological behaviour of multiple tissues simultaneously, thereby providing a means to study changes that occur through healthy ageing and disease such as osteoarthritis. As a result significant research investment has been placed in developing such models of the human knee. Previous work has highlighted that model predictions are highly sensitive to the various inputs used to build them, particularly the mathematical definition of material properties of biological tissues. The goal of this systematic review is two-fold. First, we provide a comprehensive summation and evaluation of existing material property data for human knee joint tissues, tabulating numerical values as a reference resource for future studies. Second, we review efforts to model whole-knee joint mechanical behaviour through finite element modelling with particular focus on how studies have sourced tissue material properties. The last decade has seen a renaissance in material testing fueled by development of a variety of new engineering techniques that allow the mechanical behaviour of both soft and hard tissues to be characterised at a spectrum of scales from nano- to bulk tissue level. As a result there now exists an extremely broad range of published values for human knee tissues. However, our systematic review highlights gaps and ambiguities that mean quantitative understanding of how tissue material properties alter with age and osteoarthritis is limited. It is therefore currently challenging to construct finite element models of the knee that are truly representative of a specific age or disease-state. Consequently, recent whole-joint finite element models have been highly generic in terms of material properties even relying on non-human data from multiple species. We highlight this by critically evaluating current ability to quantitatively compare and model 1) young and old and 2) healthy and osteoarthritis human knee joints. We suggest that future research into both healthy and diseased knee function will benefit greatly from a subject- or cohort-specific approach in which finite element models are constructed using material properties, medical imagery and loading data from cohorts with consistent demographics and/or disease states.

Extended “LMPHETS” Finite Element Models for Coupled Mechano-Electro-Chemical Transport in Soft Tissues

2002 ◽  
Author(s):  
B. R. Simon ◽  
G. A. Radtke ◽  
P. H. Rigby ◽  
S. K. Williams ◽  
Z. P. Liu
Keyword(s):  
Finite Element ◽  
Soft Tissues ◽  
Electrical Potential ◽  
Fluid Pressure ◽  
Nonlinear Material ◽  
Solid Matrix ◽  
Test Problems ◽  
Finite Element Models ◽  
Material Interfaces ◽  
Mobile Species

Soft tissues are hydrated fibrous materials that exhibit nonlinear material response and undergo finite straining during in vivo loading. A continuum model of these structures (“LMPHETS” [1,2]) is a porous solid matrix (with charges fixed to the solid fibers) saturated by a mobile fluid (water) and multiple species (e.g., three mobile species designated by α, β = p, m, b where p = +, m = −, and b = ± charge) dissolved in the mobile fluid. A “mixed” LMPHETS theory and finite element models (FEMs) were presented [1] in which the “primary fields” are the displacements, ui = xi − Xi and the mechano-electro-chemical potentials, ν˜ξ* (ξ, η = f, e, m, b) that are continuous across material interfaces. “Secondary fields” (discontinuous at material boundaries) are mechanical fluid pressure, pf; electrical potential, μ˜e; and concentration or “molarity”, cα = dnα / dVf. Here an extended version of these models is described and numerical results are presented for representative test problems associated with transport in soft tissues.

scholarly journals Finite element simulation of elastohydrodynamic lubrication of soft biological tissues

2007 ◽  
Vol 85 (11-14) ◽  
pp. 1114-1120 ◽  
Author(s):  
Taraneh Moghani ◽  
James P. Butler ◽  
Judy Li-Wen Lin ◽  
Stephen H. Loring
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Elastohydrodynamic Lubrication ◽  
Biological Tissues ◽  
Soft Biological Tissues ◽  
Element Simulation

scholarly journals Modelling indentation of human lower-limb soft tissue: simulation parameters and their effects

2020 ◽  
Author(s):  
Theodoros Marinopoulos ◽  
Lorenzo Zani ◽  
Simin Li ◽  
Vadim V. Silberschmidt
Keyword(s):  
Finite Element ◽  
Mechanical Behaviour ◽  
Lower Limb ◽  
Soft Tissues ◽  
High Sensitivity ◽  
Biological Tissues ◽  
Finite Element Models ◽  
Mechanical Responses ◽  
Reaction Forces ◽  
Human Participants

Abstract Modern developments of biomedical applications demand a better understanding of mechanical behaviour of soft biological tissues. As human soft tissues demonstrate a significant structural and functional diversity, characterisation of their mechanical behaviour still remains a challenge. Limitations related with implementation of mechanical experiments on human participants lead to a use of finite-element models for analysis of mechanical responses of soft tissues to different loads. This study focuses on parameters of numerical simulation considered for modelling of indentation of a human lower limb. Assessment of the effect of boundary conditions on the model size shows that at a ratio of its length to the tissue’s thickness of 1.7 for the 3D model this effect vanishes. The numerical results obtained with models employing various sets of mechanical parameters of the first-order Ogden scheme were compared with original experimental data. Furthermore, high sensitivity of the resulting reaction forces to the indenting direction is demonstrated for cases of both linear and angular misalignments of the indenter. Finally, the effect of changes in material parameters and their domain on their contribution to the reaction forces is discussed with the aim to improve our understanding of mechanical behaviour of soft tissues based on numerical methods. The undertaken research with its results on minimal requirements for finite-element models of indentation of soft tissues can support inverse analysis of their mechanical properties and underpin orthopaedic and medical procedures.

Forced Response of Disks due to Distributed Pressure Fields

2001 ◽  
Author(s):  
A. H. Mohamad ◽  
J. Ravoux ◽  
G. Jacquet-Richardet
Keyword(s):  
Finite Element ◽  
Finite Element Modeling ◽  
Analytical Model ◽  
Forced Response ◽  
Major Influence ◽  
Finite Element Models ◽  
Circular Plates ◽  
Element Modeling ◽  
Pressure Fields ◽  
Distributed Pressure

Abstract The shape and the frequency of excitation, induced by distributed pressure fields, have both a major influence on the associated response of bladed disks. The way those pressure fields are considered by finite element models have then to be as accurate as possible. In this paper, an analytical model, adapted to the prediction of the forced response of clamped-free circular plates, due to distributed pressure fields, is first derived. This model is considered as a reference in order to assess the effectiveness of different finite element modeling.

Automated Estimation of Elastic Material Parameters of a Transversely Isotropic Material Using Asymmetric Indentation and Inverse Finite Element Analysis

2015 ◽  
Author(s):  
Yuan Feng ◽  
Chung-Hao Lee ◽  
Lining Sun ◽  
Ruth J. Okamoto ◽  
Songbai Ji
Keyword(s):  
Finite Element ◽  
Soft Tissues ◽  
Transverse Isotropy ◽  
Transversely Isotropic ◽  
Biological Tissues ◽  
Fiber Reinforced ◽  
Element Analysis ◽  
Soft Biological Tissues ◽  
Tissue Properties ◽  
Brain White Matter

Anisotropy exists in many soft biological tissues. The most common anisotropy is transverse isotropy, which is typical for fiber-reinforced structures, such as the brain white matter, tendon and muscle. Although many methods have been proposed to determine tissue properties, techniques to characterize transversely isotropic materials remain limited. The goal of this study is to investigate the feasibility of asymmetric indentation coupled with numerical optimization based on inverse finite element (FE) simulation to characterize transversely isotropic soft biological tissues. The proposed approach combining indentation and optimization may provide a useful general framework to characterize a variety of fiber-reinforced soft tissues in the future.

A STUDY ON THE EFFECT OF COLLAGEN FIBER ORIENTATION ON MECHANICAL RESPONSE OF SOFT BIOLOGICAL TISSUES

2015 ◽  
Vol 76 (7) ◽  
Author(s):  
Farshid Fathi ◽  
Shahrokh Shahi ◽  
Soheil Mohammadi
Keyword(s):  
Finite Element ◽  
Soft Tissues ◽  
Mechanical Response ◽  
Strain Energy Function ◽  
Soft Materials ◽  
Biological Tissues ◽  
Soft Biological Tissues ◽  
Proposed Model ◽  
The Matrix ◽  
Element Approach

Extensive research has been performed in the past decades to study the behavior of soft biological tissues in order to reduce the need for practical experiments. The applicability of these researches, particularly for skin, ligament, muscles and the heart, brings up its importance in various biological science and technology disciplines such as surgery and medicine. Softness and large deformation govern the behavior of soft materials and prohibit the use of small strains solutions in finite element method.In this work, the focus is set on a strain energy function which has the advantage of accurately representing the behavior of a variety of soft tissues with only a few parameters in a finite element approach. The numerical results are verified with a set of tensile experiments to demonstrate the performance of the proposed model. The parameters include the matrix and collagen bundles and their orientation. Different cases are analyzed and discussed for better prediction of different soft tissue responses.  

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