Degree Of Fiber Alignment Research Articles

Two‐stage annealing method for short carbon fiber‐reinforced nylon 6 in fused filament fabrication

AbstractThe mechanical properties of short carbon fiber‐reinforced nylon 6 (CF‐PA6) components formed by fused filament fabrication (FFF) are significantly affected by the process parameters of additive manufacturing and heat treatment. In this study, the effects of printing speed, carbon fiber aspect ratio, and annealing temperature on fiber orientation were investigated by observation of single‐layer‐single‐fiber samples. Furthermore, a two‐stage annealing process was proposed to increase the tensile modulus of CF‐PA6 based on the correlation analysis results between the degree of fiber alignment and the variation of tensile modulus. According to the calculation of the Pearson correlation coefficient, the tensile modulus was highly correlated with the degree of fiber alignment under different printing speeds and fiber aspect ratios. The variation in tensile modulus and fiber orientation was also consistent when the annealing temperature was lower than the crystallization temperature. Conversely, the variation of tensile modulus and fiber orientation were opposite, as the annealing temperature was higher than the crystallization temperature because of the influence of crystallinity. Through increasing the degree of fiber alignment and crystallinity of the parts, the proposed two‐stage annealing method could increase the tensile modulus of the parts to 9.0 GPa, which was 16.81% higher than that of single‐temperature annealing.Highlights The effects of annealing temperature, carbon fiber aspect ratio and printing speed on fiber orientation were illustrated. The relationship between the degree of fiber alignment and the variation of tensile modulus was established. The proposed two‐stage annealing method, considering fiber orientation and crystallinity, significantly increased the tensile modulus of CF270‐PA6 parts from 7.7 to 9.0 GPa. The quantitative analysis of the fiber orientation is realized by the statistical analysis of the plane fiber orientation angle of the single‐layer‐single‐fiber sample.

2D or not 2D? Mapping the in-depth inclination of the collagen fibers of the corneoscleral shell

The collagen fibers of the corneoscleral shell play a central role in the eye mechanical behavior. Although it is well-known that these fibers form a complex three-dimensional interwoven structure, biomechanical and microstructural studies often assume that the fibers are aligned in-plane with the tissues. This is convenient as it removes the out-of-plane components and allows focusing on the 2D maps of in-plane fiber organization that are often quite complex. The simplification, however, risks missing potentially important aspects of the tissue architecture and mechanics. In the cornea, for instance, fibers with high in-depth inclination have been shown to be mechanically important. Outside the cornea, the in-depth fiber orientations have not been characterized, preventing a deeper understanding of their potential roles. Our goal was to characterize in-depth collagen fiber organization over the whole corneoscleral shell. Seven sheep whole-globe axial sections from eyes fixed at an IOP of 50 mmHg were imaged using polarized light microscopy to measure collagen fiber orientations and density. In-depth fiber orientation distributions and anisotropy (degree of fiber alignment) accounting for fiber density were quantified over the whole sclera and in 15 regions: central cornea, peripheral cornea, limbus, anterior equator, equator, posterior equator, posterior sclera and peripapillary sclera on both nasal and temporal sides. Orientation distributions were fitted using a combination of a uniform distribution and a sum of π-periodic von Mises distributions, each with three parameters: primary orientation μ, fiber concentration factor k, and weighting factor a. To study the features of fibers that are not in-plane, i.e., fiber inclination, we quantified the percentage of inclined fibers and the range of inclination angles (half width at half maximum of inclination angle distribution). Our measurements showed that the fibers were not uniformly in-plane but exhibited instead a wide range of in-depth orientations, with fibers significantly more aligned in-plane in the anterior parts of the globe. We found that fitting the orientation distributions required between one and three π-periodic von Mises distributions with different primary orientations and fiber concentration factors. Regions of the posterior globe, particularly on the temporal side, had a larger percentage of inclined fibers and a larger range of inclination angles than anterior and equatorial regions. Variations of orientation distributions and anisotropies may imply varying out-of-plane tissue mechanical properties around the eye globe. Out-of-plane fibers could indicate fiber interweaving, not necessarily long, inclined fibers. Effects of small-scale fiber undulations, or crimp, were minimized by using tissues from eyes at high IOPs. These fiber features also play a role in tissue stiffness and stability and are therefore also important experimental information.

Creep of particle and short fibre reinforced polyurethane rubber

Tensile stress–strain testing and creep testing have been carried out on a polyurethane rubber, at three temperatures, with and without either particulate or short fibre alumina reinforcement. A previous paper reported concerning composites with particulate reinforcement and the present work is focused on the effect of the fibres. The samples were made via a blending and extrusion process that produced a certain degree of fibre alignment (along the direction of loading). Prior milling procedures were used to produce fibres with two different ranges of aspect ratio (with averages about 10 and 16). When expressed as true stress–strain relationships, all materials exhibit approximately linear responses. The dependence of stiffness on the volume fraction and aspect ratio of the reinforcement was found to conform well to the Eshelby model predictions. Moreover, the creep behaviour of all of the materials can be captured well by a Miller–Norton formulation, using the average matrix stress predicted by the Eshelby model. A striking conclusion is that it is both predicted and observed that short fibres are much more effective in reducing the creep rate than is the case with particles.

An investigation into the polylactic acid texturization through thermomechanical processing and the improved d33 piezoelectric outcome of the fabricated scaffolds

The bio/sensors performance has been established to be significantly affected through partially or entirely alignment of nano/microfibrous in polymeric mats. The matter of crystalline/amorphous proportion in semicrystalline polymers is another factor that can affect the application of the piezoelectric patches. The present work deals with fabricating the scaffolds of micro/nanofibers through a modified electrospinning procedure. The ratio of the relevant organic and polar solvents, the beading, the degree of fiber alignment, and fiber thickness have been intentionally elaborated. An unaligned unbeaded nanofibrous mat has been fabricated after tuning the solvents to poly-lactic acid ratio. This paper, for the first time, deals with the calculation of the value of d33 value of a commercial PLA and its improvement, it has been revealed that the d33 piezoelectric property is improved as a consequence of the thermo-mechanical processing above the cold crystallization temperature. The applied thermo (mechanical) processing causes the structural evolution from amorphous to crystallized states. Formation of the α and α′ crystalline phases is introduced as the main responsible for the improvement of the piezoelectric property. This improvement not only is correlated with the degree of crystallinity, but also the orientation and alignment of the crystallites is known to be influential. In this respect, the complex helical chain structural evolution of poly-lactic acid has been analyzed through Herman's orientation function. It has been found that, besides the characterized disorder-to-order phase transformation, the CO branched out dipoles interactions significantly affects by the texturization of the aligned polymeric chains in the direction of the electrospinning which is known as the main factor to promote the piezoelectric property of processed mat.

In Situ Characterization of Polycaprolactone Fiber Response to Quasi-Static Tensile Loading in Scanning Electron Microscopy.

Microstructural responses to the mechanical load of polymers used in tissue engineering is notably important for qualification at in vivo testing, although insufficiently studied, especially regarding promising polycaprolactone (PCL). For further investigations, electrospun PCL scaffolds with different degrees of fiber alignment were produced, using two discrete relative drum collector velocities. Development and preparation of an adjusted sample geometry enabled in situ tensile testing in scanning electron microscopy. By analyzing the microstructure and the use of selected tracking techniques, it was possible to visualize and quantify fiber/fiber area displacements as well as local fractures of single PCL fibers, considering quasi-static tensile load and fiber alignment. The possibility of displacement determination using in situ scanning electron microscopy techniques for testing fibrous PCL scaffolds was introduced and quantified.

Characterization of degree of alignment of polymer microfibers electrospun on a rotating water collector

In this study, the degree of alignment of polymer microfibers produced by electrospinning using a rotating water collector was evaluated. Aligned micro- and nano-fibers are required in various practical applications involving anisotropic properties. The degree of fiber alignment has many significant effects; hence, and accurate quantitative analysis of fiber alignment is necessary. Therefore, this study developed a simple and efficient method based on two-dimensional fast Fourier transform, followed by ellipse fitting. As a demonstrative example, the polymer microfibers were electrospun on the rotating water collector as the alignment of microfibers can be easily controlled. The analysis shows that the flow velocity of the liquid collector significantly affects the electrospun microfiber alignment, that is, the higher the flow velocity of the liquid collector, the greater is the degree of microfiber alignment. This method can be used for analyzing the fiber alignment in various fields such as smart sensors, fibers, composites, and textile engineering.

Effect of electrospinning parameters on the mechanical and morphological characteristics of small diameter PCL tissue engineered blood vessel scaffolds having distinct micro and nano fibre populations – A DOE approach

Electrospinning is a widely used technique in tissue engineered blood vessel (TEBV) scaffold research. Successful TEBV scaffolds must be produced in a way that balances tissue-like mechanical characteristics with morphologies that promote cellularity by supporting cell attachment whilst also permitting cell infiltration. Electrospun tubular poly (ε-caprolactone) (PCL) scaffolds combining interspersed nano and micro fibre morphologies have shown promise in this regard. A comprehensive design of experiments (DOE) approach examines the effect of production parameters on the mechanical and morphological properties of small diameter PCL vascular scaffolds created using a single-step electrospinning process and comprised of multi-modal fibre populations. Mechanical properties of the vessels are assessed using a modified uniaxial ringlet tensile test method while morphological properties, including mean fibre diameter, degree of fibre alignment and porosity, are also captured.Regression analysis showed that a diverse range of mechanical properties could be achieved through the careful adjustment of processing conditions. Constructs with a broad range of ultimate tensile strengths (~4–10 MPa) and Young's moduli (~1.5–3 MPa) were prepared. The speed of the rotating collector system was found to be a dominant factor influencing both the mechanical and morphological attributes of the fabricated scaffolds. Several other main effects and interactions terms were found to influence the scaffold attributes, including degree of fibre orientation and mean fibre diameter.The potential applicability of particular tubular scaffolds for vascular applications were then evaluated by comparison with literature obtained mechanical property values for human coronary arteries and the great saphenous vein. This study demonstrates an important step towards a readily available and tailorable set of multi-modal PCL scaffold designs for further biological and clinical investigation.

Highly sensitive humidity-responsive actuator comprising aligned electrospun fibers containing metal–organic framework nanoparticles

A humidity-responsive bilayer actuator was fabricated using the electrospinning method. We fabricated a polyvinylpyrrolidone (PVP)/poly(acrylic acid) (PAA) active layer with different alignments of fibers and thicknesses, and combined them with polyimide film. We observed the bending motion of the actuator while the relative humidity varied from 10% to 80%. While the PVP/PAA layer was electrospun with an increase in collecting speed and time, the degree of fiber alignment and the film thickness increased, respectively. We observed that a well-aligned or thick actuator exhibited a higher change in curvature throughout the experiment. However, a thick actuator had low sensitivity to relative humidity changes because of the low diffusion rate. To overcome this drawback, we added metal–organic framework (MOF) nanoparticles to the PVP/PAA solution before electrospinning to enhance the sensitivity of the actuator. As a result, the MOF-actuator was highly sensitive to humidity and showed larger curvature changes, generating a high actuating force of approximately 5.5 mN at the same thickness as the bare PVP/PAA actuator. We believe that the introduced actuator can be applied in robotics, energy harvesting, and sensors with controllable performance and high actuating force.

Temporal Impact of Substrate Anisotropy on Differentiating Cardiomyocyte Alignment and Functionality.

Anisotropic biomaterials can affect cell function by driving cell alignment, which is critical for cardiac engineered tissues. Recent work, however, has shown that pluripotent stem cell-derived cardiomyocytes may self-align over long periods of time. To determine how the degree of biomaterial substrate anisotropy impacts differentiating cardiomyocyte structure and function, we differentiated mouse embryonic stem cells to cardiomyocytes on nonaligned, semialigned, and aligned fibrous substrates and evaluated cell alignment, contractile displacement, and calcium transient synchronicity over time. Although cardiomyocyte gene expression was not affected by fiber alignment, we observed gradient- and threshold-based differences in cardiomyocyte alignment and function. Cardiomyocyte alignment increased with the degree of fiber alignment in a gradient-based manner at early time points and in a threshold-based manner at later time points. Calcium transient synchronization tightly followed cardiomyocyte alignment behavior, allowing highly anisotropic biomaterials to drive calcium transient synchronization within 8 days, while such synchronized cardiomyocyte behavior required 20 days of culture on nonaligned biomaterials. In contrast, cardiomyocyte contractile displacement had no directional preference on day 8 yet became anisotropic in the direction of fiber alignment on aligned fibers by day 20. Biomaterial anisotropy impact on differentiating cardiomyocyte structure and function is temporally dependent. Impact Statement This work demonstrates that biomaterial anisotropy can quickly drive desired pluripotent stem cell-derived cardiomyocyte structure and function. Such an understanding of matrix anisotropy's time-dependent influence on stem cell-derived cardiomyocyte function will have future applications in the development of cardiac cell therapies and in vitro cardiac tissues for drug testing. Furthermore, our work has broader implications concerning biomaterial anisotropy effects on other cell types in which function relies on alignment, such as myocytes and neurons.

Superior mechanical enhancement of epoxy composites reinforced by polyimide nanofibers via a vacuum-assisted hot-pressing

High performance epoxy composites are highly required in many applications. In this work, polyimide electrospun nanofibers (PIENFs) with excellent thermal and mechanical properties were used to reinforce the epoxy matrix by a vacuum-assisted hot-pressing procedure. The morphologies of PIENFs and PI/epoxy composites were investigated by scanning electron microscopy (SEM). Thermogravimetric analyses (TGA) was used to characterize the thermal properties of PI/epoxy composites and calculated the actual weight amount of PIENFs in the composites. The effects of nanofiber amount and the degree of fiber alignment on the mechanical properties of PI/epoxy composites have been studied. Owing to the superior mechanical performance of PIENFs and the strong interfacial adhesion, the PI/epoxy composites presented significantly mechanical improvement as compared to the pure epoxy.

Fiber Orientation Control by Stretching in Cellulose Nanofiber Green Composites

The presence of nanoscale cellulosic fiber; namely cellulose nanofiber, increases year by year because the mechanical and physical properties are believed to be comparable to those of common glass fibers. On the other hand, most of the reported strength data for the cellulose nanofiber-reinforced polymeric composite materials was not as high as expected. In order to obtain high-strength cellulose nanofiber-reinforced polymer composites, we tried to optimize the fiber orientation of cellulose nanofibers in poly (vinyl alcohol)-based polymer matrix by using a repeated mechanical stretching treatment. The fiber orientation of cellulose nanofibers in the poly (vinyl alcohol) matrix can be modified by changing the total amount of stretching strain applied during the multiple stretching treatments. The degree of fiber alignment was directly evaluated by observing the cellulose nanofibers on the sample surface with a digital microscope. The efficacy of proposed nanofiber alignment control has been explored experimentally and theoretically. The tensile strength and modulus of the cellulosic nanocomposites after applying the multiple stretching treatments increased by approximately 80% and 40% respectively, as compared with those of the untreated nanocomposites.

Optimization of rotating-jet electrospinning process using response surface methodology

Rotating-jet electrospinning method is one of the efficient techniques for producing aligned nanofibers. This paper reports an accurate investigation on the influence of collector diameter (CD), voltage, polymer concentration (PC), and insulator length (IL) of spinneret on the degree of fiber alignment (DFA), production rate of fiber, and fiber diameter. The polymer solution was a mixture of polyacrylonitrile and N,N-dimethylformamide. The ranges of independent variables were 20–50 cm for CD, 10–22 kV for voltage, 13–19 wt% for PC, and 0.5–3 cm for IL. To minimize the number of required experiments for a complete evaluation, response surface methodology (RSM) and central composite rotatable design were applied by means of Expert Design Software. After defining the upper and lower bounds of the above independent variables in the software, 30 unique experiments were delivered. The recommended operating conditions by the software were exactly applied in the laboratory and the corresponding values for the DFA, production rate, and fiber diameter were measured. The nanofiber morphology was examined by scanning electron microscopy (SEM). By applying the least-squares method in the DX7.0.0 software, well-fitting polynomial correlations to the experimental results were obtained, and using these correlations, the influence of independent variables and responses was comprehensively studied. Finally, the best values of independent variables for optimizing the responses were determined using RSM.

Preparation of 3D Collagen Gels and Microchannels for the Study of 3D Interactions <em>In Vivo</em>

Historically, most cellular processes have been studied in only 2 dimensions. While these studies have been informative about general cell signaling mechanisms, they neglect important cellular cues received from the structural and mechanical properties of the local microenvironment and extracellular matrix (ECM). To understand how cells interact within a physiological ECM, it is important to study them in the context of 3 dimensional assays. Cell migration, cell differentiation, and cell proliferation are only a few processes that have been shown to be impacted by local changes in the mechanical properties of a 3-dimensional ECM. Collagen I, a core fibrillar component of the ECM, is more than a simple structural element of a tissue. Under normal conditions, mechanical cues from the collagen network direct morphogenesis and maintain cellular structures. In diseased microenvironments, such as the tumor microenvironment, the collagen network is often dramatically remodeled, demonstrating altered composition, enhanced deposition and altered fiber organization. In breast cancer, the degree of fiber alignment is important, as an increase in aligned fibers perpendicular to the tumor boundary has been correlated to poorer patient prognosis1. Aligned collagen matrices result in increased dissemination of tumor cells via persistent migration2,3. The following is a simple protocol for embedding cells within a 3-dimensional, fibrillar collagen hydrogel. This protocol is readily adaptable to many platforms, and can reproducibly generate both aligned and random collagen matrices for investigation of cell migration, cell division, and other cellular processes in a tunable, 3-dimensional, physiological microenvironment.

Preparation of 3D Collagen Gels and Microchannels for the Study of 3D Interactions In Vivo.

Historically, most cellular processes have been studied in only 2 dimensions. While these studies have been informative about general cell signaling mechanisms, they neglect important cellular cues received from the structural and mechanical properties of the local microenvironment and extracellular matrix (ECM). To understand how cells interact within a physiological ECM, it is important to study them in the context of 3 dimensional assays. Cell migration, cell differentiation, and cell proliferation are only a few processes that have been shown to be impacted by local changes in the mechanical properties of a 3-dimensional ECM. Collagen I, a core fibrillar component of the ECM, is more than a simple structural element of a tissue. Under normal conditions, mechanical cues from the collagen network direct morphogenesis and maintain cellular structures. In diseased microenvironments, such as the tumor microenvironment, the collagen network is often dramatically remodeled, demonstrating altered composition, enhanced deposition and altered fiber organization. In breast cancer, the degree of fiber alignment is important, as an increase in aligned fibers perpendicular to the tumor boundary has been correlated to poorer patient prognosis(1). Aligned collagen matrices result in increased dissemination of tumor cells via persistent migration(2,3). The following is a simple protocol for embedding cells within a 3-dimensional, fibrillar collagen hydrogel. This protocol is readily adaptable to many platforms, and can reproducibly generate both aligned and random collagen matrices for investigation of cell migration, cell division, and other cellular processes in a tunable, 3-dimensional, physiological microenvironment.

A simple method for fabrication of electrospun fibers with controlled degree of alignment having potential for nerve regeneration applications

In peripheral nerve injuries where direct suturing of nerve endings is not feasible, nerve regeneration has been facilitated through the use of artificially aligned fibrous scaffolds that provide directional growth of neurons to bridge the gap. The degree of fiber alignment is crucial and can impact the directionality of cells in a fibrous scaffold. While there have been multiple approaches that have been used for controlling fiber alignment, however, they have been associated with a compromised control on other properties, such as diameter, morphology, curvature, and topology of fibers. Therefore, the present study demonstrates a modified electrospinning set-up, that enabled fabrication of electrospun fibers with controlled degree of alignment from non-aligned (NA), moderately aligned (MA, 75%) to highly aligned (HA, 95%) sub-micron fibers while keeping other physical properties unchanged. The results demonstrate that the aligned fibers (MA and HA) facilitated directional growth of human astrocytoma cells (U373), wherein the aspect ratio of cells was found to increase with an increase in degree of fibers alignment. In contrast to NA and MA fibers, the HA fibers showed improved contact guidance to U373 cells that was demonstrated by a significantly higher cell aspect ratio and nuclear aspect ratio. In conclusion, the present study demonstrated a modified electrospinning setup to fabricate differentially aligned fibrous scaffolds with the HA fibers showing potential for use in neural tissue engineering.

The anisotropic mechanical behaviour of electro-spun biodegradable polymer scaffolds: Experimental characterisation and constitutive formulation

Electro-spun biodegradable polymer fibrous structures exhibit anisotropic mechanical properties dependent on the degree of fibre alignment. Degradation and mechanical anisotropy need to be captured in a constitutive formulation when computational modelling is used in the development and design optimisation of such scaffolds.Biodegradable polyester-urethane scaffolds were electro-spun and underwent uniaxial tensile testing in and transverse to the direction of predominant fibre alignment before and after in vitro degradation of up to 28 days. A microstructurally-based transversely isotropic hyperelastic continuum constitutive formulation was developed and its parameters were identified from the experimental stress–strain data of the scaffolds at various stages of degradation.During scaffold degradation, maximum stress and strain in circumferential direction decreased from 1.02±0.23MPa to 0.38±0.004MPa and from 46±11% to 12±2%, respectively. In longitudinal direction, maximum stress and strain decreased from 0.071±0.016MPa to 0.010±0.007MPa and from 69±24% to 8±2%, respectively. The constitutive parameters were identified for both directions of the non-degraded and degraded scaffold for strain range varying between 0% and 16% with coefficients of determination r2>0.871. The six-parameter constitutive formulation proved versatile enough to capture the varying non-linear transversely isotropic behaviour of the fibrous scaffold throughout various stages of degradation.

Rapid Quantification of 3D Collagen Fiber Alignment and Fiber Intersection Correlations with High Sensitivity.

Metastatic cancers aggressively reorganize collagen in their microenvironment. For example, radially orientated collagen fibers have been observed surrounding tumor cell clusters in vivo. The degree of fiber alignment, as a consequence of this remodeling, has often been difficult to quantify. In this paper, we present an easy to implement algorithm for accurate detection of collagen fiber orientation in a rapid pixel-wise manner. This algorithm quantifies the alignment of both computer generated and actual collagen fiber networks of varying degrees of alignment within 5°°. We also present an alternative easy method to calculate the alignment index directly from the standard deviation of fiber orientation. Using this quantitative method for determining collagen alignment, we demonstrate that the number of collagen fiber intersections has a negative correlation with the degree of fiber alignment. This decrease in intersections of aligned fibers could explain why cells move more rapidly along aligned fibers than unaligned fibers, as previously reported. Overall, our paper provides an easier, more quantitative and quicker way to quantify fiber orientation and alignment, and presents a platform in studying effects of matrix and cellular properties on fiber alignment in complex 3D environments.

Oriented nanofibrous membranes for tissue engineering applications: Electrospinning with secondary field control

Electrospinning is an electrical field driven method to produce polymer fibre membranes by deposition of a charged polymer jet onto a grounded collector. Fibre alignment within these mats is usually achieved by a fast collector movement, which is not feasible for all collector geometries, such as small diameter tubes or free-form moulds. The aim of this study was to evaluate the use of charged deflector plates to apply a dynamic, alternating electrical field perpendicular to the spinning direction, in order to directly control the fibre trajectory. Different field signal types, deflector plate voltages and deflection frequency ranges have been investigated. 210 poly(ɛ)caprolactone (PCL) membranes were electrospun. SEM images of each membrane were analysed using ImageJ. Main fibre diameter and orientation, as well as the degree of fibre alignment, were calculated, while a subset of the spun scaffolds were tested for their tensile properties. Higher deflector plate voltage amplitude resulted in a better fibre alignment. The best alignment was observed in a low deflection frequency range from 2 to 10 Hz. Mean main fibre direction was 87±18°, relative to the deflection axis, while fibre alignment had only a minor effect on the average fibre diameter. Young′s modulus and yield stress increased with the ratio of the parallel fibre component. The feasibility of the described method to achieve fibre alignment was demonstrated. However, the main fibre direction is not aligned with the deflection axis, but consistently perpendicular to it, which is also reflected in the tensile properties of spun samples.

Quantitative analysis of three-dimensional fibrillar collagen microstructure within the normal, aged and glaucomatous human optic nerve head.

The aim of this study was to quantify connective tissue fibre orientation and alignment in young, old and glaucomatous human optic nerve heads (ONH) to understand ONH microstructure and predisposition to glaucomatous optic neuropathy. Transverse (seven healthy, three glaucomatous) and longitudinal (14 healthy) human ONH cryosections were imaged by both second harmonic generation microscopy and small angle light scattering (SALS) in order to quantify preferred fibre orientation (PFO) and degree of fibre alignment (DOFA). DOFA was highest within the peripapillary sclera (ppsclera), with relatively low values in the lamina cribrosa (LC). Elderly ppsclera DOFA was higher than that in young ppsclera (p < 0.00007), and generally higher than in glaucoma ppsclera. In all LCs, a majority of fibres had preferential orientation horizontally across the nasal–temporal axis. In all glaucomatous LCs, PFO was significantly different from controls in a minimum of seven out of 12 LC regions (p < 0.05). Additionally, higher fibre alignment was observed in the glaucomatous inferior–temporal LC (p < 0.017). The differences between young and elderly ONH fibre alignment within regions suggest that age-related microstructural changes occur within the structure. The additional differences in fibre alignment observed within the glaucomatous LC may reflect an inherent susceptibility to glaucomatous optic neuropathy, or may be a consequence of ONH remodelling and/or collapse.

Transport properties of electrospun fibrous membranes with controlled anisotropy

In-plane gas permeability measurements were performed on electrospun polyacrilonitrile fibrous mats. Samples were cast onto a drum rotating at various speeds in order to create materials with different degrees of fiber alignment. Permeability measurements were made in both parallel and perpendicular directions and large increases were seen for flow in the fiber direction as expected. Because these measurements were performed in-plane it was necessary to mechanically compress the samples during measurement. Tests were performed at several compressed thicknesses, but it was found that the samples did not compress uniformly so it was not possible to determine a unique Carman–Kozeny constant for the material. A methodology was developed by which the Carman–Kozeny constant was determined for each compression that produced a linear trend against compressed porosity. It was proposed that the true Carman–Kozeny constant for the material can be determined by extrapolating this trend to the value of the uncompressed porosity, and good agreement with the literature values was obtained.