Anisotropic Fiber Orientation Research Articles

Characterisation of Anisotropic Fibre Orientation in Composites by Means of X-Ray Grating Interferometry Computed Tomography

In this work carbon fibre-reinforced polymer (CFRP) laminates and short glass fibre- reinforced polymers (sGFRP) were investigated by means of X-ray scatter dark field imaging (SDFI) using Talbot-Lau grating interferometer computed tomography. For the characterisation of the laminate structures of CFRP the anisotropic properties of the small angle scattering signal was used to image fibre bundles running in different directions. SDFI allows the visualisation of the weave pattern structure of a carbon fibre bundle in three dimensions, even if the individual fibres cannot be separated or the absorption contrast between the carbon fibres and the epoxy resin matrix is very low. For the investigated sGFRP samples qualitative information about local fibre anisotropies within a specimen were obtained by SDFI. Due to the complex behaviour of fibre alignment during the injection process a clear interpretation of the SDFI signals was difficult. As a reference method, all samples were scanned by means of high resolution cone beam Computed Tomography (µXCT). For the sGFRP the combination of µXCT and appropriate software tools provides local fibre orientations and allows three-dimensional visualisation by colour coding each extracted fibre.

Computational analysis of the electromechanical consequences of short QT syndrome.

Computational analysis of the electromechanical consequences of short QT syndrome.

Snail1-expressing fibroblasts in the tumor microenvironment display mechanical properties that support metastasis.

Crosstalk between tumor and stromal cells in the tumor microenvironment alter its properties in ways that facilitate the invasive behavior of tumor cells. Here, we demonstrate that cancer-associated fibroblasts (CAF) increase the stiffness of the extracellular matrix (ECM) and promote anisotropic fiber orientation, two mechanical signals generated through a Snail1/RhoA/αSMA-dependent mechanism that sustains oriented tumor cell migration and invasiveness. Snail1-depleted CAF failed to acquire myofibroblastic traits in response to TGFβ, including RhoA activation, αSMA-positive stress fibers, increased fibronectin fibrillogenesis, and production of a stiff ECM with oriented fibers. Snail1 expression in human tumor-derived CAF was associated with an ability to organize the ECM. In coculture, a relatively smaller number of Snail1-expressing CAF were capable of imposing an anisotropic ECM architecture, compared with nonactivated fibroblasts. Pathologically, human breast cancers with Snail1(+) CAF tended to exhibit desmoplastic areas with anisotropic fibers, lymph node involvement, and poorer outcomes. Snail1 involvement in driving an ordered ECM was further confirmed in wound-healing experiments in mice, with Snail1 depletion preventing the anisotropic organization of granulation tissue and delaying wound healing. Overall, our results showed that inhibiting Snail1 function in CAF could prevent tumor-driven ECM reorganization and cancer invasion.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

GEF-H1 controls focal adhesion signaling that regulates mesenchymal stem cell lineage commitment

Focal adhesions (FAs) undergo maturation that culminates in size and composition changes that modulate adhesion, cytoskeleton remodeling and differentiation. Although it is well recognized that stimuli for osteogenesis of mesenchymal stem cells (MSCs) drive FA maturation, actin organization and stress fiber polarization, the extent to which FA-mediated signals regulated by the FA protein composition specifies MSC commitment remains largely unknown. Here, we demonstrate that, upon dexamethasone (osteogenic induction) treatment, guanine nucleotide exchange factor H1 (GEF-H1, also known as Rho guanine nucleotide exchange factor 2, encoded by ARHGEF2) is significantly enriched in FAs. Perturbation of GEF-H1 inhibits FA formation, anisotropic stress fiber orientation and MSC osteogenesis in an actomyosin-contractility-independent manner. To determine the role of GEF-H1 in MSC osteogenesis, we explore the GEF-H1-modulated FA proteome that reveals non-muscle myosin-II heavy chain-B (NMIIB, also known as myosin-10, encoded by MYH10) as a target of GEF-H1 in FAs. Inhibition of targeting NMIIB into FAs suppresses FA formation, stress fiber polarization, cell stiffness and osteogenic commitments in MSCs. Our data demonstrate a role for FA signaling in specifying MSC commitment.

Phenomenological improvements to predictive models of fiber orientation in concentrated suspensions

The standard Folgar-Tucker (FT) orientation equation is a useful method for theoretically determining isotropic fiber orientation in concentrated suspensions. However, when quantitatively compared with related experimental observations, this equation demonstrates an over-prediction inaccuracy. Recently, the Phelps-Tucker anisotropic rotary diffusion (ARD) model has shown an ability to handle primary anisotropic fiber orientation. Nevertheless, the ARD tensor depending upon Hand's tensor is difficult to apply in general, because numerous parameters themselves are so sensitive as to affect the stability of any numerical results. To address these critical problems in predicting fiber orientation, this study proposes an improved ARD tensor combined with a new retardant principal rate (iARD-RPR) model. The RPR model is a coaxial correction of the orientation tensor for the FT equation. In addition, the iARD tensor, consisting of an identity tensor and a dimensionless fiber-rotary-resistance tensor, is more concise with two available parameters. As a validation, the iARD-RPR model nicely fits the orientation tensor components measured in transient simple shear flows. Of particular importance is the good agreement between the predictive fiber orientation distribution and the practical core-shell structure for the center-gated disk of injection molding of fiber-reinforced thermoplastics.

Termination of pinned vortices by high-frequency wave trains in heartlike excitable media with anisotropic fiber orientation

A variety of chemical and biological nonlinear excitable media, including heart tissue, exhibit vortices (spiral waves) that can anchor to nonexcitable obstacles. Such anchored vortices can be terminated by the application of high-frequency wave trains, as shown previously in isotropic excitable media. In this study, we examined the basic dependencies of the conduction velocities of planar waves and waves around curved obstacles as a function of anisotropy through numerical simulations of excitable media that mimic the fiber orientation in a real heart. We also investigated the unpinning of anchored spiral waves by high-frequency wave trains in an anisotropic excitable medium. Unlike the findings regarding the termination of spiral waves in isotropic excitable systems, we found a nonmonotonic relationship between the maximum unpinning period and the obstacle radius depending on the fiber orientation, where the formation of unwanted secondary pinned vortices or chaotic waves is seen over a wide range of parameters.

Influence of carding and drawing processes on orientation of fibers in slivers

The orientation of fibers is known to play a very important role in determining the quality of the carded and drawn slivers as well as the quality of the ultimate yarns produced from those slivers. Also, the orientation of fibers is considered to be a very useful parameter for evaluating the effectiveness of the carding and drawing processes in aligning the fibers. In addition, the orientation of fibers is known to determine the length utilization of the fibers in the slivers. This article reports on the influence of carding and drawing processes on the orientation of fibers in the carded and drawn slivers. A series of carded and drawn slivers were prepared by using polyester staple fibers and making various changes in the carding and drawing processes and the orientation of fibers in the slivers was evaluated based on Lindsley’s methodology in conjunction with a mathematical model of fiber orientation in slivers. It was observed that the increase in cylinder speed and the decrease in doffer speed resulted in more anisotropic fiber orientation distribution in the carded slivers and the degree of anisotropy was found to be more in the forward direction as compared to the backward direction of the carded slivers. The higher draft and doubling in the drawframe resulted in higher anisotropy in the orientation of fibers in the drawn slivers and the drawn slivers displayed more anisotropy in the backward direction as compared to the forward direction. The higher delivery speed of the drawframe resulted in higher anisotropy in fiber orientation in the drawn slivers and the drawn slivers exhibited more anisotropy in the backward direction as compared to the forward direction. The results of fiber orientation in the carded and drawn slivers obtained by using the mathematical model were compared to the fiber orientation parameters suggested by earlier researchers and a satisfactory correlation between them was observed.

Creep of experimental short fiber-reinforced composite resin

The purpose of this study was to investigate the reinforcing effect of short E-glass fiber fillers oriented in different directions on composite resin under static and dynamic loading. Experimental short fiber-reinforced composite resin (FC) was prepared by mixing 22.5 wt% of short E-glass fibers, 22.5 wt% of resin, and 55 wt% of silane-treated silica fillers. Three groups of specimens (n=5) were tested: FC with isotropic fiber orientation, FC with anisotropic fiber orientation, and particulate-filled composite resin (PFC) as a control. Time-dependent creep and recovery were recorded. ANOVA revealed that after secondary curing in a vacuum oven and after storage in dry condition for 30 days, FC with isotropic fiber orientation (1.73%) exhibited significantly lower static creep value (p<0.05) than PFC (2.54%). For the different curing methods and storage conditions evaluated in this study, FC achieved acceptable static and dynamic creep values when compared to PFC.

Enhanced Biochemical and Biomechanical Properties of Scaffolds Generated by Flock Technology for Cartilage Tissue Engineering

Natural cartilage shows column orientation of cells and anisotropic direction of collagen fibers. However, matrices presently used in matrix-assisted autologous chondrocyte implantation do not show any fiber orientation. Our aim was to develop anisotropic scaffolds with parallel fiber orientation that were capable to support a cellular cartilaginous phenotype in vitro. Scaffolds were created by flock technology and consisted of a membrane of mineralized collagen type I as substrate, gelatine as adhesive, and parallel-oriented polyamide flock fibers vertically to the substrate. Confocal laser scan microscopy demonstrated that mesenchymal stem cells (MSCs) adhered and proliferated well in the scaffolds and cell vitality remained high over time. Articular chondrocytes seeded in a collagen type I gel into flock scaffolds deposited increasing amounts of proteoglycans and collagen type II over time. MSC-seeded flock scaffold constructs under chondrogenic conditions deposited significantly more proteoglycans and collagen type II than MSC collagen type I gel constructs only. Biomechanical testing revealed higher initial hardness of flock scaffolds than that of a clinically applied collagen type I/III scaffold combined with superior relaxation and an increasing hardness in MSC-loaded flock biocomposites during chondrogenesis. In conclusion, flock technology allows fabrication of scaffolds with anisotropic fiber orientation that mediates superior biomechanical and biochemical composition of tissue engineering constructs for cartilage repair.

MRI assessment of cartilage ultrastructure

In T2-weighted MRI images joint cartilage can appear laminated. The multilaminar appearance is visualized as zones of different intensity. This appearance is based on the dipolar interaction of water molecules within cartilage zones of different collageneous network structures. Therefore, the MR visualization of zones of anisotropic arrangement of the collagen fibers depends upon their orientation to the static magnetic field (magic-angle effect). The aim of this article is to demonstrate the potential of high-resolution MRI for characterizing cartilage network structuring and biomechanical properties. Information equivalent to that from polarization light microscopy can be derived noninvasively. Based on NMR microscopic (microMRI) data, potential new possibilities of MRI for quantitative assessment of collagen structuring and intracartilagenous load distribution are presented. These methods use MR intensity angle dependence and load influence on cartilage visualization. Alternatively to the determination of mechanical parameters from cartilage deformation, it is demonstrated that stress distribution and biomechanical properties can be derived in principle from the local intensity variation of anisotropic fiber orientation zones. The limitations with respect to a clinical application of the proposed methods are discussed.

Fibre structure and anisotropy of glass reinforced thermoplastics

Abstract The fibre structure and orientation distribution of two commercially available glass mat thermoplastics reinforced by continuous glass fibre was studied to investigate the anisotropic behaviour under compression moulding and mechanical loading, and to investigate the influence of the fibre structure and orientation on the anisotropic behaviour. Circular samples were deformed into ellipses when moulded, due to the anisotropic fibre orientation. The fibre content and orientation were examined in different locations of the elliptically deformed specimens. X-ray pictures were taken of the material in order to develop images of the fibres, before and after compression moulding. In another procedure, the matrix was burned off and the fibre network structures were studied in each case. A CCD camera was used to scan the fibres as digital images to measure the orientation distribution functions of the fibres. The fibre orientation measuring process was facilitated by subroutines implemented in the source code of the public domain NIH-image analysis software using simulated Fraunhofer diffraction.

The two-way interaction between anisotropic flow and fiber orientation in squeeze flow

The rheology of a discontinuous fiber filled polypropylene in squeeze flow between parallel plates is studied. The material has an initial anisotropic fiber orientation distribution and therefore displays a strongly anisotropic in-plane flow behavior with predominant flow transverse to the axis of principal orientation. The kinematic field is computed using a linear, orthotropic constitutive model, where the fibers are assumed to move affinely with the surrounding fluid. The fiber orientation distribution is updated in each timestep thus coupling orientation and flow. Two different orientation descriptions are evaluated: orientation tensors with closure approximations, and a technique based on direct solution of the orientation of a set of test fibers. The two methods are first compared to exact solutions of the orientation distribution function in simple shear and pure extension; the direct solution is exact within numerical error, whereas the methods based on orientation tensors and quadratic and hybrid closure fail to correctly describe any transient fiber orientation evolution. Finally, the orientation representations are implemented in the kinematic model and compared to the experimental data; the direct solution method is found to give a very accurate prediction of the observed flow kinematics, whereas the other techniques result in substantial errors.

Effects of fiber orientation on strain concentrations in glass reinforced polyamides

AbstractOrientation of reinforcement fibers in injection molded parts is a key factor in determining their strength and stiffness: therefore stress‐strain analyses based on isotropic material models produce only rough results. We present a flow/strain analysis methodology that accounts for the actual anisotropic material properties and fiber orientation. Material properties are determined by experiment, fiber orientation is inferred from flow simulation results (velocity vectors). Stress/strain fields are calculated by means of finite element analysis. Results show that for notched parts molded from short glass reinforced polyamide resin, there is a significant dependence of the strain concentration on the local fiber orientation resulting from different injection molding conditions.

Damage process modeling on SMC

The damage processes taking place in SMC, which has been subjected to monotonically increasing tensile loads, are analyzed and the stress-strain curves are calculated. SMC is viewed as a laminate consisting of fiber bundles embedded in a resin/filler matrix. The stiffness of bundles and matrix is expected to be influenced by developing cracks, which lead to a reduction of the total stiffness of the SMC. Crack creation, and consequent bundle and matrix stiffness reduction, are viewed as a statistical process. The quadratic criterion in stress space and the maximum strain criterion are used to predict failure in the fiber bundles and in the matrix, respectively. Residual stresses resulting from the high curing temperatures, anisotropic fiber orientation, and varying content of filler particles in the matrix, inside and outside of the fiber bundles, are taken into account. The comparison of predicted stress-strain curves to experimental results, obtained on almost 20 different SMC materials, shows very good agreement, especially at elongations less than 1%. The model developed in this work allows us to appreciate quantitatively the influence of different material and processing parameters on the behavior of SMC, and in this way, to optimize its composition. © 1996 John Wiley & Sons, Inc.