Random Fiber Orientation Research Articles

Effective Moduli Evaluation of Carbon Nanotube Reinforced Polymers Using Micromechanics

A multistep homogenization method is adopted to compute the effective moduli of carbon nanotube reinforced composites. The composite is assumed to be reinforced with isolated individual fibers and clustered fibers. A uniform agglomeration model is introduced assuming constant carbon nanotube cluster size throughout the matrix. Agglomeration volume fraction—a critical parameter in the simulation—is considered to be an explicit function of inter-particle distance and quality of dispersion of fibers. The micromechanics model also incorporates random fiber orientation using a statistical approach. It is seen that these parameters reduce the stiffening effect of carbon nanotubes significantly in the composite.

Impact Behavior of Apus Bamboo (<i>Gigantochloa apus</i>) Fiber/Epoxy Green Composites

The objective of this work is to investigate the impact behavior of bamboo fiber/epoxy composites. The test was carried out in accordance with the ASTM D5941 Izod impact test standard. Whilst the fiber was obtained from local bamboo the matrix being used is Eposchon general purpose Bisphenol A-epichlorohydrin epoxy resin mixed with Eposchon general purpose Polyaminoamide epoxy hardener. The specimens were cut from nine bamboo fiber/epoxy composite panels. Each panel contains either random or unidirectional fiber orientation of four different volume fraction,i.e. 10, 20, 30 and 40%, of fiber, along with a pure epoxy, without fiber, panel board as reference. According to the adopted standard, the specimens are of prismatic bars of 85 [mm] long × 10 [mm] wide × 5 [mm] thick. Photo macrographs of selected samples were analyzed to describe their failure modes. It was revealed that both the impact strength and energy absorption capacity of the samples increase with the increase of fiber content up to 40%, for both unidirectional and randomly oriented fiber arrangement. In addition, unidirectional fiber composite samples show higher values in both impact strength and energy absorption capacity (0.162 [J.mm-2] and 8.5 [J], respectively) in comparison with those of randomly oriented fiber composite samples (0.144 [J.mm-2] and 7.6 [J], respectively).

Electrospun scaffolds for multiple tissues regeneration in vivo through topography dependent induction of lineage specific differentiation

Physical topographic cues from various substrata have been shown to exert profound effects on the growth and differentiation of stem cells due to their niche-mimicking features. However, the biological function of different topographic materials utilized as bio-scaffolds in vivo have not been rigorously characterized. This study investigated the divergent differentiation pathways of mesenchymal stem cells (MSCs) and neo-tissue formation trigged by aligned and randomly-oriented fibrous scaffolds, both in vitro and in vivo. The aligned group was observed to form more mature tendon-like tissue in the Achilles tendon injury model, as evidenced by histological scoring and collagen I immunohistochemical staining data. In contrast, the randomly-oriented group exhibited much chondrogenesis and subsequent bone tissue formation through ossification. Additionally, X-ray imaging and osteocalcin immunohistochemical staining also demonstrated that osteogenesis in vivo is driven by randomly oriented topography. Furthermore, MSCs on the aligned substrate exhibited tenocyte-like morphology and enhanced tenogenic differentiation compared to cells grown on randomly-oriented scaffold. qRT-PCR analysis of osteogenic marker genes and alkaline phosphatase (ALP) staining demonstrated that MSCs cultured on randomly-oriented fiber scaffolds displayed enhanced osteogenic differentiation compared with cells cultured on aligned fiber scaffolds. Finally, it was demonstrated that cytoskeletal tension release abrogated the divergent differentiation pathways on different substrate topography. Collectively, these findings illustrate the relationship between topographic cues of the scaffold and their inductive role in tissue regeneration; thus providing an insight into future development of smart functionalized bio-scaffold design and its application in tissue engineering.

Determination of material properties for short fibre reinforced C/C-SiC

Determining the mechanical properties of short fibre reinforced CMC using standard sized coupons has always been a challenge due to a high statistical scattering of the measured values. Although the random orientation of short fibres results in a quasi-isotropic material behavior of 2D-structures with a sufficiently large volume, the small volume typical for test coupons usually results in a non-isotropic fibre orientation in the tested volume. This paper describes a method for manufacturing unidirectional oriented short fibre reinforced CMC materials and presents material properties of UD-C/C-SiC. After verifying the fibre orientation of the CMC using micro-computed tomography, coupons were extracted to determine the orthotropic material properties. These orthotropic material properties were then used to predict the properties of C/C-SiC with randomly distributed short fibres. To validate the method, micro-computed tomography is used to quantitatively determine the fibre orientation within coupons extracted from randomly distributed short fibre C/C-SiC. After mechanical three-point-bending tests, the measured stiffness and bending strength is compared with the predicted properties. Finally, the data are used to devise a method suited for reducing the inherent large spread of material properties associated with the measurement of CMC materials with randomly distributed short fibres.

Structural performance of steel fibre reinforced concrete — Part III. Behaviour in tension

The present paper of a series deals with the experimental characterisation of tensile splitting strength and compressive behaviour of different structural concrete containing different volume of steel fibre reinforcement (0 V%, 0.5 V%, 1.0 V%, 75 kg/m3, 150 kg/m3) and different configuration of steel fibres (crimped, hooked-end). Tensile splitting tests were carried out on standard cylinder (∅ = 150 mm, l = 300 mm) specimens (so-called Brazilian test) considering random fibre orientation. Since the fibre orientation may significantly affect the tensile behaviour test series were also performed on cross-section (100 mm × 100 mm) of steel fibre reinforced concrete beams (100 mm × 100 mm × 240 mm) sawn out of steel fibre reinforced slab elements. Taken as a whole behaviour of steel fibre reinforced concrete was examined in tension taking into consideration different experimental parameters such as fibre content, type of fibres, fibre configuration, fibre orientation, size of specimens (size effect) and concrete mixture.

The effects of nanofiber diameter and orientation on siRNA uptake and gene silencing

While substrate topography influences cell behavior, RNA interference (RNAi) has also emerged as a potent method for understanding and directing cell fate. However, the effects of substrate topography on RNAi remain poorly understood. Here, we report the influence of nanofiber architecture on siRNA-mediated gene-silencing in human somatic and stem cells. The respective model cells, human dermal fibroblasts (HDFs) and mesenchymal stem cells (MSCs), were cultured onto aligned or randomly oriented electrospun poly(ε-caprolactone) fibers of different average diameters (300 nm, 700 nm and 1.3 μm). In HDFs, decreasing fiber diameter from 1.3 μm to 300 nm improved Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and Collagen-I silencing efficiencies by ∼ 3.8 and ∼4.4 folds respectively (p < 0.05) while the effective siRNA uptake pathway was altered from clathrin-dependent endocytosis to macropinocytosis. In MSCs, aligned fibers generated significantly higher level of gene silencing of RE-1 silencing transcription factor (REST) and green fluorescent protein (GFP) (∼1.6 and ∼1.5 folds respectively, p < 0.05), than randomly-oriented fibers. Aligned fiber topography facilitated functional siRNA uptake through clathrin-mediated endocytosis and membrane fusion. Taken together, our results demonstrated a promising role of three-dimensional fibrous scaffolds in modulating siRNA-mediated gene-silencing and established the critical synergistic role of these substrates in modulating cellular behavior by RNAi.

Effect of fiber orientation on the shear behavior of glass fiber/epoxy composites

This paper deals with the study of the influence of the lay-up configuration on interlaminar and in-plane shear properties of glass fiber reinforced epoxy composites. The following laminates were produced by resin transfer molding with vacuum assistance for this study: [0]5, [90]5, [0/90/0/90/0] and randomly oriented (mat). The composites, with similar overall fiber volume fraction, were evaluated based on four tests: double-notched shear, short beam shear, V-notched rail and Iosipescu shear tests. Besides, the dynamic shear modulus was measured with non-destructive testing based on free vibration method. The [0]5 laminate presented interlaminar shear strength almost twice that of [90]5, whereas the mat samples presented higher in-plane shear strength in both tests used due to its random fiber orientation. The dynamic shear modulus was higher for the composites [0]5, as expected due to the longitudinally oriented fibers. Among the shear test methods applied, double-notched and V-notched methods exhibited more auspicious features, possibly due to a more uniform shear stress state during testing.

Flexural Modeling of Steel Fiber-Reinforced Concrete Members: Analytical Investigations

AbstractThis paper presents an analytical model for the determination of the ultimate flexural capacity of steel fiber-reinforced (SFR) concrete rectangular sections and their associated crack width using the principles of strain compatibility and force equilibrium. The proposed model considers an elastic perfect-plastic model for compression and an elastic constant postpeak response of SFR concrete in tension. Unlike other flexural models available in the literature, the proposed model considers in the analysis the random distribution and orientation of steel fibers at a cracked section. The model was verified using existing experimental results, and it fairly predicted the flexural capacity of the SFR concrete beams. A parametric study using the proposed model was conducted to assess the effect of the fiber parameters and the strength of the concrete on the ultimate flexural capacity of a section and its associated crack widths. A normalized design chart is also presented to simplify the analysis proced...

Fabrication of Tubular Scaffolds with Controllable Fiber Orientations Using Electrospinning for Tissue Engineering

Tubular scaffolds with controllable fiber orientations are fabricated by electrospinning with a conductive rotating drum in the presence of a parallel or orthogonal conductive wire. A higher rotational speed of the drum results in thinner fibers and a more aligned fibrous structure. The fiber orientation can be further precisely controlled by the design of a conductive wire capable of guiding the deposition of electrospun fibers. Parallel or orthogonal fiber orientations in the tubular scaffolds are achieved using an orthogonal or parallel conductive wire, respectively, at a high rotational speed of the drum. Cell culture on the scaffolds with random, parallel, and orthogonal fiber orientations reveals that the degree of stretching of the fibroblast is highly affected by the fiber orientations.

Structural performance of steel fibre reinforced concrete — Part II. Compressive behaviour and stress-strain relationship

Abstract The present paper of a series deals with the experimental characterisation of compressive strength and compressive behaviour (stress-strain relationship) of different structural concrete containing different volume of steel fibre reinforcement (0 V%, 0.5V%, 1.0V%, 75 kg/m3, 150 kg/m3) and different configuration of steel fibres (crimped, hooked-end). Compressive tests were carried out on standard cube (150 mm × 150 mm × 150 mm) and cylinder (Ø = 150 mm, l = 300 mm) specimens considering random fibre orientation. Since the fibre orientation may significantly affect the compressive behaviour, test series were also performed on cylinders (Ø = 70 mm, l = 100 mm) drilled out of fibre reinforced concrete beams and prisms (100 mm × 100 mm × 240 mm) sawn out of steel fibre reinforced deep beams. Throughout the tests stress-strain relationships were registered on the standard cube and cylinder specimens as well. In conclusion, behaviour of steel fibre reinforced concrete was examined in compression taking into consideration different experimental parameters such as fibre content, type of fibres, fibre configuration, fibre orientation, size of specimens (size effect) and concrete mixture.

Dry Sliding Wear Behaviour of Magnesium Alloy Based Hybrid Composites in Transverse Direction

Wear behaviour of AE42 Mg alloy-based composites reinforced with Saffil short fibres (SSF) and SiC particles (SiCp) in various combinations has been investigated in transverse direction, i.e., the plane containing random fibre-orientation was parallel to the steel counter-face. Wear tests are conducted on a pin-on-disc set-up under dry sliding condition having a constant sliding velocity of 0.837 m/s for a constant sliding distance of 2.5 km in the load range of 10-40 N. It is observed that the hybrid composites reinforced with both SSF and SiCp exhibit better wear resistance than the composite reinforced with SSF alone, because SiCp are harder than SSF and remain intact retaining their load bearing capacity even at the highest load employed in the present investigation. The dominant wear mechanism is observed to be abrasion for all the composites. It is accompanied by fracture and pull-out of SSF from the worn surfaces. Wear behaviour of the composites in transverse direction is also compared with wear behaviour in longitudinal direction, i.e., the plane containing random fibre-orientation was perpendicular to the steel counter-face, reported earlier by the same authors. It is observed that the wear resistance of the composites in transverse direction is lower than that in longitudinal direction due to the lower load bearing capacity, the extensive fracture and pull-out of SSF from the worn surfaces.

The effect of general statistical fiber misalignment on predicted damage initiation in composites

A micromechanical method is employed for the prediction of unidirectional composites in which the fiber orientation can possess various statistical misalignment distributions. The method relies on the probability-weighted averaging of the appropriate concentration tensors, which are established by the micromechanical procedure. This approach provides access to the local field quantities throughout the constituents, from which initiation of damage in the composite can be predicted. In contrast, a typical macromechanical procedure can determine the effective composite elastic properties in the presence of statistical fiber misalignment, but cannot provide the local fields. Fully random fiber distribution is presented as a special case using the proposed micromechanical method. Results are given that illustrate the effects of various amounts of fiber misalignment in terms of the standard deviations of in-plane and out-of-plane misalignment angles, where normal distributions have been employed. Damage initiation envelopes, local fields, effective moduli, and strengths are predicted for polymer and ceramic matrix composites with given normal distributions of misalignment angles, as well as fully random fiber orientation.

Effect of fiber orientation of collagen-based electrospun meshes on human fibroblasts for ligament tissue engineering applications.

Within the past two decades polylactic-co-glycolic acid (PLGA) has gained considerable attention as a biocompatible and biodegradable polymer that is suitable for tissue engineering and regenerative medicine. In this present study, we have investigated the potential of PLGA, collagen I (ColI), and polyurethane (PU) scaffolds for ligament tissue regeneration. Two different ratios of PLGA (50:50 and 85:15) were used to determine the effects on mechanical tensile properties and cell adhesion. The Young's modulus, tensile stress at yield, and ultimate tensile strain of PLGA(50:50)-ColI-PU scaffolds demonstrated similar tensile properties to that of ligaments found in the knee. Whereas, scaffolds composed of PLGA(85:15)-ColI-PU had lower tensile properties than that of ligaments. Furthermore, we investigated the effect of fiber orientation on mechanical properties and our results indicate that aligned fiber scaffolds demonstrate higher tensile properties than scaffolds with random fiber orientation. Also, human fibroblasts attached and proliferated with no need for additional surface modifications to the presented electrospun scaffolds in both categories. Collectively, our investigation demonstrates the effectiveness of electrospun PLGA scaffolds as a suitable candidate for regenerative medicine, capable of being manipulated and combined with other polymers to create three-dimensional microenvironments with adjustable tensile properties to mimic native tissues.

Determination of the fiber-size distribution function in polydisperse dielectric fibrous materials

A simple method has been proposed for determining the average fiber length in unit volume of a polydisperse fibrous material as depending on fiber diameter. The method consists in the measurement of light attenuation as a function of the distance from an examined sample. The method entails comparison of the measured energy fluxes that reach a detector before and after scattering by an examined fibrous material sample and uses an integral relation that expresses the intensity of light transmitted through a random medium via the electric-field correlation function. Formulas have been found for the electric-field correlation function after the passage through a layer of a polydisperse fibrous material with random arrangement and orientation of fibers. The obtained correlation function enables one to derive an integral equation that expresses the logarithmic ratio of the energy fluxes reaching the radiation detector before and after the passage through a scattering medium via the fiber size-distribution function. Solution of this integral equation makes it possible to determine the fiber-size distribution function from the light attenuation measured as depending on the distance from the point of observation. Experiments have been carried out for several fibrous filters and relevant calculations have been presented. The results of the solution of the integral equation agree with the data obtained by other experimental methods and with visual processing of electron micrographs.

Improved mechanical properties and hydrophilicity of electrospun nanofiber membranes for filtration applications by dopamine modification

Electrospun nanofiber membranes (ENMs) are an emerging platform for membrane filtration; however, widespread applications of ENMs are hindered by poor mechanical strength attributed to their high porosity, intrinsically low, random fiber orientations and weak interactions between fiber junctions. In addition to suitable mechanical properties, most water-based filtration processes require membranes to be hydrophilic in order to resist fouling and enhance water flow. In this study, we demonstrate a simple chemical modification capable of improving the mechanical properties of polyacylonitrile (PAN) and polysulfone (PSu) ENMs. The chemical modification involves the polydopamine (PDA), a hydrophilic polymer. PDA has the dual benefit of hydrophilization and strengthening of ENMs to improve their wettability and tolerance to operational and handling conditions. When deposited onto the fibers, PDA promotes bonding between fibers by coating junction points throughout the nonwoven. The coated nonwoven membranes showed a 100 to 300% increases in tensile strength and Young׳s Modulus with no decrease in flexibility while retaining their porous structure and high water permeability. For hydrophobic PSu ENMs, the hydrophilicity was also significantly improved after coating.

Electrospun Gelatin Constructs with Tunable Fiber Orientation Promote Directed Angiogenesis

The field of therapeutic angiogenesis has been predominantly concentrated in modalities that incorporate pro-angiogenic growth factors and/or cells within polymeric constructs that are implanted into the ischemic region. There is growing evidence that construct architecture can significantly affect growth factor activity, cellular viability and differentiation potential. Electrospinning is an attractive but simple scaffold fabrication technique that offers several advantages over traditional fabrication approaches to prepare highly organized structures for therapeutic angiogenesis applications. We recently described the fabrication of nanofibrous scaffolds with aligned fiber orientation that directed cell migration and orientation (i.e.human umbilical vein endothelial cells). Herein we demonstrate the ability of bFGF containing nanofibrous gelatin B scaffolds with controlled fiber orientation to promote capillary formation in vivo. Aligned scaffolds loaded with bFGF induced the highest levels of reperfusion (73% increased in LDPI ratios by day 21 post ischemia induction) in comparison to all other groups including scaffolds with random fiber orientation. Furthermore, the newly formed vasculature, assessed by confocal microscopy, had a parallel alignment along the axis of the scaffold’s fibers. In contrast, no vessel directionality was observed in the animals treated with scaffolds with random fiber orientation in the presence or absence of bFGF.

Optimization of fiber distribution in fiber reinforced composite by using NURBS functions

This research deals with the optimization of short fibers distribution in continuum structures made of Fiber Reinforced Composite (FRC) by adopting an efficient gradient based optimization approach. Motivated by lack of non-heuristic and mesh independent optimization algorithms to obtain the optimum distribution of short fibers through a design domain, Non-Uniform Rational B-spline (NURBS) basis functions have been implemented to define continuous and smooth mesh independent fiber distribution function as well as domain discretization. Thanks to higher order (here quadratic) NURBS basis functions along with their compact support, a drastic reduction in computational time has been obtained by increasing mesh size while the accuracy of the model is maintained. Moreover combination of NURBS with sensitivity based optimization method allows a fast convergence to optimum fiber distribution layout. Minimization of elastic strain energy and maximization of fundamental frequency have been considered as objective functions for static and free vibration problems, respectively; to get the maximum fiber exploitation in the structural element. Nodal volume fraction of fiber was defined as the optimization design variable while a homogenization approach based on the random orientation of short fibers in the matrix has been adopted. Some numerical examples related to the structural response under static loading as well as the free vibration behavior are finally conducted to demonstrate the capability and reliability of the model.

Synergy of fiber length and content on free vibration and damping behavior of natural fiber reinforced polyester composite beams

This work addresses the results of experimental investigation carried out on free vibration characteristics of short sisal fiber (SFPC) and short banana fiber (BFPC) polyester composites. Influence of fiber length and weight percentage on mechanical properties and free vibration characteristics are analyzed. Composite beam specimen is fabricated with random fiber orientations at17MPa compression using compression molding machine. Natural frequencies and associated modal damping values of the composite laminates were obtained by carrying out the experimental modal analysis. It is found that an increase in fiber content increases the mechanical and damping properties. For SFPC, 3mm fiber length and 50wt% fiber content yielded better properties, whereas for BFPC, 4mm fiber length and 50wt% fiber content was the best combination. Scanning electron microscopy was performed to study the interfacial mechanism.

Shape-memory-actuated change in scaffold fiber alignment directs stem cell morphology

Tissue engineering scaffolds have traditionally been static physical structures poorly suited to mimicking the complex dynamic behavior of in vivo microenvironments. Here we present a thermoresponsive scaffold that can be programmed to change macroscopic shape and microscopic architecture during cell culture. The scaffold, which was prepared by electrospinning a shape memory polymer (SMP), was used to test the hypothesis that a shape-memory-actuated change in scaffold fiber alignment could be used to control the behavior of attached and viable cells. To test this hypothesis, we stretched an SMP scaffold of randomly oriented fibers and fixed the scaffold in a temporary but stable elongated shape in which fibers were aligned by the strain. Following seeding and culture of human adipose-derived stem cells on the strain-aligned scaffold, the scaffold was triggered to transition back to its initial shape and random fiber orientation via shape memory actuation using a cytocompatible temperature increase. We found that cells preferentially aligned along the fiber direction of the strain-aligned scaffold before shape memory actuation. After shape memory actuation, cells remained attached and viable but lost preferential alignment. These results demonstrate that shape-memory-actuated changes in scaffold fiber alignment can be achieved with attached and viable cells and can control cell morphological behavior. The incorporation of shape memory into cytocompatible scaffolds is anticipated to facilitate the development, delivery and functionality of tissue engineering scaffolds and the in vitro and in vivo study and application of mechanobiology.

Two-nozzle electrospinning of (MWNT/PU)/PU nanofibrous composite mat with improved mechanical and thermal properties

Composite nanofibrous mat composed of neat polyurethane (PU) and multiwalled carbon nanotubes/polyurethane (MWNT/PU) nanofibers have been fabricated by one-step angled two-nozzle electrospinning. The morphological, thermal, and mechanical properties of the electrospun nanofibers were evaluated. The diameters of electrospun neat PU and composite nanofibers ranged from 239 to 1058 nm. The two-nozzle electrospun (MWNT/PU)/PU composite nanofibers showed curly, and randomly-oriented fibers with interfiber bonding, and were generally bigger in size than single-nozzle electrospun nanofibers. The tensile strength of the neat PU composite nanofiber mat obtained from two-nozzle electrospinning was 25% higher than that obtained from neat PU single-nozzle electrospinning. The incorporation of MWNTs in the composite nanofiber increased the tensile strength by as much as 64% without reducing elongation, made the composite nanofiber more thermally stable, and improved the melting zone. The present results showed that side-by-side angled two-nozzle electrospinning can improve the quality of the electrospun nanofibers that could have potential application in different fields such as filtration, protective clothing and tissue engineering.