scholarly journals INFLUENCE OF LEAFLET’S MATRIX STIFFNESS AND FIBER ORIENTATION ON THE OPENING DYNAMICS OF A PROSTHETIC TRILEAFLET HEART VALVE

2017 ◽  
Vol 17 (06) ◽  
pp. 1750096 ◽  
Author(s):  
ANDREA AVANZINI
Keyword(s):  
Fiber Orientation ◽  
Mechanical Response ◽  
Strain Energy Function ◽  
Effective Orifice Area ◽  
Matrix Stiffness ◽  
Soft Matrix ◽  
Long Time ◽  
Valve Dynamics ◽  
Lower Maximum ◽  
Opening Phase

Biological valves are employed for aortic valve substitution since a long time but there is a growing effort toward the development of new engineered tissues, in which the complex mechanical response of native leaflets is replicated using composite materials consisting of a soft matrix with embedded reinforcing fibers. The main goal of the present study is to investigate the influence that variations on fiber orientation and matrix stiffness may have on valve dynamics. To this aim, a fluid–structure interaction (FSI) model of a trileaflet valve was implemented in which the opening phase was simulated and leaflet matrix stiffness and fiber orientation were varied in the framework of an anisotropic hyperelastic strain energy function. Results show that both parameters may affect significantly transvalvular pressure gradient and effective orifice area (EOA). For the opening phase of the valve examined, less favorable flow conditions were found when preferred fiber orientation is circumferential, due to lower maximum EOA achievable. Such configuration in combination with stiffer matrix may result in significant degradation of valve performances. Overall fiber orientation can potentially be taylored to optimize valve dynamics, provided also structural aspects that may be prominent in the closure phase, are considered.

Wrinkling of a Fiber-Reinforced Membrane

2008 ◽  
Vol 76 (1) ◽  
Author(s):  
E. Shmoylova ◽  
A. Dorfmann
Keyword(s):  
Boundary Conditions ◽  
Energy Function ◽  
Mechanical Response ◽  
Transverse Isotropy ◽  
Base Material ◽  
Strain Energy Function ◽  
Transversely Isotropic ◽  
Incompressible Material ◽  
Fiber Reinforced ◽  
Relaxed Energy

In this paper we investigate the response of fiber-reinforced cylindrical membranes subject to axisymmetric deformations. The membrane is considered as an incompressible material, and the phenomenon of wrinkling is taken into account by means of the relaxed energy function. Two cases are considered: transversely isotropic membranes, characterized by one family of fibers oriented in one direction, and orthotropic membranes, characterized by two family of fibers oriented in orthogonal directions. The strain-energy function is considered as the sum of two terms: The first term is associated with the isotropic properties of the base material, and the second term is used to introduce transverse isotropy or orthotropy in the mechanical response. We determine the mechanical response of the membrane as a function of fiber orientations for given boundary conditions. The objective is to find possible fiber orientations that make the membrane as stiff as possible for the given boundary conditions. Specifically, it is shown that for transversely isotropic membranes a unique fiber orientation exists, which does not affect the mechanical response, i.e., the overall behavior is identical to a nonreinforced membrane.

Numerical Implementation and Finite Element Analysis of Anisotropic Hyperelastic Biomaterials - Influence of Fibers Orientation

2013 ◽  
Vol 554-557 ◽  
pp. 2414-2423 ◽  
Author(s):  
Rachid Djeridi ◽  
Mohand Ould Ouali
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Fiber Orientation ◽  
Mechanical Response ◽  
Theoretical Study ◽  
Constitutive Law ◽  
Anisotropic Behavior ◽  
Element Analysis ◽  
Material Parameters ◽  
Fibers Orientation

Modeling anisotropic behavior of fiber reinforced rubberlike materials is actually of a great interest in many industrials sectors. Indeed, accurately description of the mechanical response and damage of such materials allows the increase of the lifecycle of these materials which generally evolve under several environment conditions. In this paper theoretical study and finite element analysis of anisotropic biomaterials is presented. The mechanical model adopted to achieve this study has been implemented into the finite element code Abaqus using an implicit scheme. This constitutive law has been utilized to perform some numerical simulations. The material parameters of the model have been determined by numerical calibration. One fiber family is considered in this work. Effects of the fiber orientation on the mechanical response and stiffness change of biomaterial is studied. Both the compressible and incompressible states have been taken into account. The results show firstly the capability of the model to reproduce the known results and that optimal fiber orientation can be found.

Large Deformation Isotropic Elasticity—On the Correlation of Theory and Experiment for Incompressible Rubberlike Solids

1973 ◽  
Vol 46 (2) ◽  
pp. 398-416 ◽  
Author(s):  
R. W. Ogden
Keyword(s):  
Mathematical Analysis ◽  
Energy Function ◽  
Strain Energy ◽  
Mechanical Response ◽  
Strain Energy Function ◽  
Usual Practice ◽  
Principal Axes ◽  
Simple Tension ◽  
Isotropic Elasticity ◽  
Strain Invariants

Abstract Many attempts have been made to reproduce theoretically the stress-strain curves obtained from experiments on the isothermal deformation of highly elastic ‘rubberlike’ materials. The existence of a strain-energy function has usually been postulated, and the simplifications appropriate to the assumptions of isotropy and incompressibility have been exploited. However, the usual practice of writing the strain energy as a function of two independent strain invariants has, in general, the effect of complicating the associated mathematical analysis (this is particularly evident in relation to the calculation of instantaneous moduli of elasticity) and, consequently, the basic elegance and simplicity of isotropic elasticity is sacrificed. Furthermore, recently proposed special forms of the strain-energy function are rather complicated functions of two invariants. The purpose of this paper is, while making full use of the inherent simplicity of isotropic elasticity, to construct a strain-energy function which: (i) provides an adequate representation of the mechanical response of rubberlike solids, and (ii) is simple enough to be amenable to mathematical analysis. A strain-energy function which is a linear combination of strain invariants defined by ϕ(α)=(α1α+α2α+α3α)/α is proposed; and the principal stretches α1, α2, and α3 are used as independent variables subject to the incompressibility constraint α1α2α3=1. Principal axes techniques are used where appropriate. An excellent agreement between this theory and the experimental data from simple tension, pure shear and equibiaxial tension tests is demonstrated. It is also shown that the present theory has certain repercussions in respect of the constitutive inequality proposed by Hill.

Modeling of Rock and Soil Aggregate under the Condition of Uniaxial Compression

2011 ◽  
Vol 243-249 ◽  
pp. 55-60
Author(s):  
Jian Ming He ◽  
Xiao Li ◽  
Teng Fei Li ◽  
Shou Ding Li
Keyword(s):  
Uniaxial Compression ◽  
Mechanical Response ◽  
Structural Characteristics ◽  
Failure Process ◽  
Soil Aggregate ◽  
Deformation And Failure ◽  
Uniaxial Test ◽  
Soft Matrix ◽  
Rock Fragments ◽  
Rock And Soil

Rock and soil aggregate (RSA) is a special geo-material and composed of hard matrix like gravel, cobble, pebble and soft matrix of soil. Discontinuity and heterogeneity are the main characteristics of RSA and its mechanical response is mainly controlled by its complex internal structure. The rock fragments play very important role in the mechanical performances under the condition of uniaxial compression and the rock content (the volume percent of rock fragments in RSA) of RSA is the focus of this study. RSA models with different rock content based on the structural characteristics were built for the numerical uniaxial test. The strength of RSA decreases instead with the increment of rock contents, stress-strain curves attained in the test reflect five different phases according to the deformation and failure process of samples.

scholarly journals Evolution of anisotropy in soft tissue

2014 ◽  
Vol 470 (2161) ◽  
pp. 20130548 ◽  
Author(s):  
J. G. Murphy
Keyword(s):  
Linear Theory ◽  
Energy Function ◽  
Anisotropic Material ◽  
Strain Energy ◽  
Mechanical Response ◽  
Essential Feature ◽  
Sufficient Conditions ◽  
Strain Energy Function ◽  
Phenomenological Approach ◽  
Reduced Form

The phenomenological approach to the modelling of the mechanical response of arteries usually assumes a reduced form of the strain-energy function in order to reduce the mathematical complexity of the model. A common approach eschews the full basis of seven invariants for the strain-energy function in favour of a reduced set of only three invariants. It is shown that this reduced form is not consistent with the corresponding full linear theory based on infinitesimal strains. It is proposed that compatibility with the linear theory is an essential feature of any nonlinear model of arterial response. Two approaches towards ensuring such compatibility are proposed. The first is that the nonlinear theory reduces to the full six-constant linear theory, without any restrictions being imposed on the constants. An alternative modelling strategy whereby an anisotropic material is compatible with a simpler material in the linear limit is also proposed. In particular, necessary and sufficient conditions are obtained for a nonlinear anisotropic material to be compatible with an isotropic material for infinitesimal deformations. Materials that satisfy these conditions should be useful in the modelling of the crimped collagen fibres in the undeformed configuration.

scholarly journals EFFECT OF FIBER ORIENTATION PATH ON THE BUCKLING, FREE VIBRATION, AND STATIC ANALYSES OF VARIABLE ANGLE TOW PANELS

2020 ◽  
Vol 18 (2) ◽  
pp. 165
Author(s):  
Nasim Fallahi ◽  
Andrea Viglietti ◽  
Erasmo Carrera ◽  
Alfonso Pagani ◽  
Enrico Zappino
Keyword(s):  
Free Vibration ◽  
Fiber Orientation ◽  
Mechanical Response ◽  
Dimensional Model ◽  
Computationally Efficient ◽  
One Dimensional ◽  
Variable Angle ◽  
Carrera Unified Formulation ◽  
Mechanical Performances ◽  
Complex Phenomena

In this work, the effect of the fiber orientation on the mechanical response of variable angle tow (VAT) panels is investigated. A computationally efficient high-order one-dimensional model, derived under the framework of the Carrera unified formulation (CUF), is used. In detail, a layerwise approach is adopted to predict the complex phenomena that may appear in VAT panels. Static, free-vibration and buckling analyses are performed, considering several material properties, geometries, and boundary conditions, and the results are assessed with those obtained using existing approaches. Considering the findings of the comparative analysis, several best design practices are suggested to improve the mechanical performances of VAT panels.

scholarly journals Matrix stiffness and blood pressure together regulate vascular smooth muscle cell phenotype switching and cofilin dependent podosome formation

2020 ◽  
Author(s):  
Brian Sit ◽  
Zhen Feng ◽  
Ioannis Xanthis ◽  
Emilie Marhuenda ◽  
Simona Zingaro ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Phenotypic Switching ◽  
Cell Phenotype ◽  
Matrix Stiffness ◽  
Cellular Mechanics ◽  
Soft Matrix ◽  
Phenotype Switch ◽  
The Impact ◽  
Progression Of Atherosclerosis

AbstractVascular smooth muscle cells (VSMCs) play a central role in the onset and progression of atherosclerosis. In pre-atherosclerotic lesions, VSMCs switch from a contractile to a synthetic phenotype and subsequently remodel the microenvironment, leading to further disease progression. Ageing and associated mechanical changes of the extracellular matrix as well as hypertension are major risk of atherosclerosis. Consequently, we sought here to systematically study the impact of mechanical and chemical stimulations on VSMC phenotypic switching. We find that the hemodynamic pressure and matrix stiffness have overlapping effects and together contribute to the phenotypic changes in cellular mechanics, podosome formation, and matrix degradation. We further identify cofilin as a key modulator of the mechanosensitive phenotype switch, which is regulated through Ca2+/slingshot-dependent pressure sensing and RhoA/ROCK-dependent stiffness sensing pathways. Altogether, microenvironment stimulations of high pressure and soft matrix collectively promote the cofilin activity, VSMC migration, and the early progression of atherosclerosis.

scholarly journals Variety of fiber orientation tensors

2021 ◽  
pp. 108128652110576
Author(s):  
Julian Karl Bauer ◽  
Thomas Böhlke
Keyword(s):  
Fiber Orientation ◽  
Mechanical Response ◽  
Transversely Isotropic ◽  
Orientation Tensor ◽  
Isotropic State ◽  
Orientation Tensors ◽  
Linear Invariant ◽  
Parameter Ranges ◽  
Independent Parameters

Fiber orientation tensors are established descriptors of fiber orientation states in (thermo-)mechanical material models for fiber-reinforced composites. In this paper, the variety of fourth-order orientation tensors is analyzed and specified by parameterizations and admissible parameter ranges. The combination of parameterizations and admissible parameter ranges allows for studies on the mechanical response of different fiber architectures. Linear invariant decomposition with focus on index symmetry leads to a novel compact hierarchical parameterization, which highlights the central role of the isotropic state. Deviation from the isotropic state is given by a triclinic harmonic tensor with simplified structure in the orientation coordinate system, which is spanned by the second-order orientation tensor. Material symmetries reduce the number of independent parameters. The requirement of positive-semi-definiteness defines admissible ranges of independent parameters. Admissible parameter ranges for transversely isotropic and planar cases are given in a compact closed form and the orthotropic variety is visualized and discussed in detail. Sets of discrete unit vectors, leading to selected orientation states, are given.

scholarly journals TRPV4 Plays a Role in Matrix Stiffness-Induced Macrophage Polarization

2020 ◽  
Vol 11 ◽  
Author(s):  
Bidisha Dutta ◽  
Rishov Goswami ◽  
Shaik O. Rahaman
Keyword(s):  
Transient Receptor Potential ◽  
Macrophage Polarization ◽  
Transient Receptor Potential Vanilloid ◽  
Polarization Spectrum ◽  
Dependent Manner ◽  
Matrix Stiffness ◽  
Soft Matrix ◽  
Genetic Ablation ◽  
M1 Macrophage

Phenotypic polarization of macrophages is deemed essential in innate immunity and various pathophysiological conditions. We have now determined key aspects of the molecular mechanism by which mechanical cues regulate macrophage polarization. We show that Transient Receptor Potential Vanilloid 4 (TRPV4), a mechanosensitive ion channel, mediates substrate stiffness-induced macrophage polarization. Using atomic force microscopy, we showed that genetic ablation of TRPV4 function abrogated fibrosis-induced matrix stiffness generation in skin tissues. We have determined that stiffer skin tissue promotes the M1 macrophage subtype in a TRPV4-dependent manner; soft tissue does not. These findings were further validated by our in vitro results which showed that stiff matrix (50 kPa) alone increased expression of macrophage M1 markers in a TRPV4-dependent manner, and this response was further augmented by the addition of soluble factors; neither of which occurred with soft matrix (1 kPa). A direct requirement for TRPV4 in M1 macrophage polarization spectrum in response to increased stiffness was evident from results of gain-of-function assays, where reintroduction of TRPV4 significantly upregulated the expression of M1 markers in TRPV4 KO macrophages. Together, these data provide new insights regarding the role of TRPV4 in matrix stiffness-induced macrophage polarization spectrum that may be explored in tissue engineering and regenerative medicine and targeted therapeutics.

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