Range Of Fiber Diameters Research Articles

Measurement of tissue scattering properties using multi-diameter single fiber reflectance spectroscopy: in silico sensitivity analysis

Multiple diameter single fiber reflectance (MDSFR) measurements of turbid media can be used to determine the reduced scattering coefficient (μ′s) and a parameter that characterizes the phase function (γ). The MDSFR method utilizes a semi-empirical model that expresses the collected single fiber reflectance intensity as a function of fiber diameter (dfiber), μ′s, and γ. This study investigated the sensitivity of the MDSFR estimates of μ′s and γ to the choice of fiber diameters and spectral information incorporated into the fitting procedure. The fit algorithm was tested using Monte Carlo simulations of single fiber reflectance intensities that investigated biologically relevant ranges of scattering properties (μ′s ∈ [0.4 – 4]mm−1) and phase functions (γ ∈ [1.4 – 1.9]) and for multiple fiber diameters (dfiber ∈ [0.2 – 1.5] mm). MDSFR analysis yielded accurate estimates of μ′s and γ over the wide range of scattering combinations; parameter accuracy was shown to be sensitive to the range of fiber diameters included in the analysis, but not to the number of intermediate fibers. Moreover, accurate parameter estimates were obtained without a priori knowledge about the spectral shape of γ. Observations were used to develop heuristic guidelines for the design of clinically applicable MDSFR probes.

Development of a compliant and cytocompatible micro‐fibrous polyethylene terephthalate vascular scaffold

Bioengineering approaches have been intensively applied to create small diameter vascular grafts using artificial materials. However, a fully successful, high performing and anti-thrombogenic structure has not been achieved yet. In this study, we have designed and fabricated a novel non-woven fibrous vascular graft with biomechanical properties closely resembling those of native vessels. Vascular cell growth, preservation of cell phenotype, retention of vasoactive properties, as well as the effect of gelatin coating on the cellular interaction with the scaffolds under static and shear stress conditions were investigated. The non-woven fibrous scaffolds were made from melt blown polyethylene terephthalate fiber webs stacked by means of a consolidation technique. The scaffold variables were fiber diameter distribution and the number of consolidated web stacks. SEM analysis confirmed various fiber diameter and pore size ranges corresponding to the different conditions. The scaffolds showed burst pressure values of ∼1500 mmHg and compliance (8.4 ± 1.0 × 10(-2) % mmHg(-1) ) very similar to those of native arteries (∼8 × 10(-2) % mmHg(-1) ). The structure with the smallest fiber diameter range (1-5 μm) and pore size range (1-20 μm) was the most suitable for the growth of human brain endothelial cells and aortic smooth muscle cells. The cells maintained their specific cell phenotype, expressed collagen and elastin and produced cAMP in response to α-calcitonin gene-related peptide. However, under shear stress conditions (0.9 dyne cm(-2) ), only 30% of the cells were retained in both uncoated and gelatin-coated scaffolds indicating the need for improving the cell retention capacity of these structures, which is our future research direction. This study indicates that the biomechanical and biocompatible properties of this novel vascular scaffold are promising for the development of a vascular graft with similar characteristics to those of native vessels.

Evaluation of the Force Required to Move a Coalesced Liquid Droplet along a Fiber

This work presents a theoretical model describing the force required to move a coalesced liquid droplet along an oleophilic filter fiber. Measurements have been made using the atomic force microscope (AFM) to examine these forces over a range of fiber and droplet diameters as well as oil properties. Good agreement between measured and modeled forces was found. The influence of droplet displacement perpendicular to the fiber on the force required to move the droplet has also been determined experimentally and theoretically. It was found that fiber surface inhomogeneities are likely to influence results. This work has also established empirical relationships that can be used to predict the force, based on a known droplet volume, for the liquid types used.

Mechanics of SFRC under tension, part II: experimental validation

This is the second of a two-part paper involving a fundamental study of the tensile stress–strain relationship of short-fibre-reinforced concrete under tension. The validation of the analytical model developed in the first part is presented here. The tensile stress–strain results obtained from the theoretical model are compared with the results obtained from the experimental investigations for a wide range of fibre lengths, diameters and volume fractions. The results of the present model are also compared with the tensile stress–strain results obtained from the existing literature. The tensile stress–strain results obtained from the proposed theoretical predictions are found to be in good agreement with the experimental results. The predictability of the analytical approach is also scrutinised for peak load, load at ultimate deformation, ductility and so on. The analytical results show a good conformity, with respect to peak load, toughness and the natures of the ascending as well as descending branches.

Structure property correlations for electrospun nanofiber nonwovens

Highly porous nonwovens composed of nanofibers and produced by electrospinning are key elements in a broad range in technical but also in Life Science areas. Applications for gas or fluid filtration, textile applications, carriers for catalysts and scaffolds for tissue engineering are selected examples. These applications require well defined nonwoven parameters such as in particular pore diameters, internal surfaces as well as permeation properties. Electrospinning, on the other hand, allows to control structural parameters such as fiber diameter, nonwoven architecture as well as in certain limits the total porosity. It is thus highly important to know as much as possible about the correlations between the structural parameters controlled by electrospinning and the parameters controlling the performance of the nonwovens composed of the electrospun nanofibers. In the present contribution we analyze these correlations for different types of electrospun nonwovens for a broad range of fiber diameters on an experimental scale The nonwoven considered are composed of polyacrylonitrile (PAN) and polyamide 6 (PA 6) fibers. Results are that pore diameters, specific surface area and permeation coefficients scale in a transparent way with fiber diameters. Finally we briefly compare these experimental results with corresponding predictions gained for ideal nonwovens predominantly from Monte Carlo simulations. The results suggest that one is able to design electrospun nanofiber based nonwovens with predetermined properties and functions in a highly controlled way.

Melt-electrospinning of PMMA

The melt electrospinning of PMMA was investigated. The averaged fiber diameter thus obtained was reduced from 34.0 µm to 19.7 µm by adding di-(2-ethylhexyl)phthalate to reduce viscosity of the molten PMMA, and it further lowered down to 4.0 µm when a KCl/ice-water solution was used as collection media. A comparison study on the PMMA fibers made through melt electrospinning and done by solution electrospinning was made. It was found that solution electrospinning was capable of fabricating very thin fibers as small as to a nanometer size, but resulted in a much wider fiber diameter range than melt-electrospinning did. In general, within some extent an increase in applied voltage and amount of the additive or a decrease in collection distance can give rise to a decreased fiber diameter and improved mechanical performance for the PMMA fibers by melt electrospinning. It was also indicated that the mechanical properties of the PMMA fibers made through melt-electrospinning were superior to those by solution elctropspinning.

Monte Carlo analysis of single fiber reflectance spectroscopy: photon path length and sampling depth

Single fiber reflectance spectroscopy is a method to noninvasively quantitate tissue absorption and scattering properties. This study utilizes a Monte Carlo (MC) model to investigate the effect that optical properties have on the propagation of photons that are collected during the single fiber reflectance measurement. MC model estimates of the single fiber photon path length (⟨LSF⟩) show excellent agreement with experimental measurements and predictions of a mathematical model over a wide range of optical properties and fiber diameters. Simulation results show that ⟨LSF⟩ is unaffected by changes in anisotropy (g ∊ [0.8, 0.9, 0.95]), but is sensitive to changes in phase function (Henyey–Greenstein versus modified Henyey–Greenstein). A 20% decrease in ⟨LSF⟩ was observed for the modified Henyey–Greenstein compared with the Henyey–Greenstein phase function; an effect that is independent of optical properties and fiber diameter and is approximated with a simple linear offset. The MC model also returns depth-resolved absorption profiles that are used to estimate the mean sampling depth (⟨ZSF⟩) of the single fiber reflectance measurement. Simulated data are used to define a novel mathematical expression for ⟨ZSF⟩ that is expressed in terms of optical properties, fiber diameter and ⟨LSF⟩. The model of sampling depth indicates that the single fiber reflectance measurement is dominated by shallow scattering events, even for large fibers; a result that suggests that the utility of single fiber reflectance measurements of tissue in vivo will be in the quantification of the optical properties of superficial tissues.

Xylem anatomy correlates with gas exchange, water-use efficiency and growth performance under contrasting water regimes: evidence from Populus deltoides x Populus nigra hybrids

Six Populus deltoides Bartr. ex Marsh. x P. nigra L. genotypes were selected to investigate whether stem xylem anatomy correlated with gas exchange rates, water-use efficiency (WUE) and growth performance. Clonal copies of the genotypes were grown in a two-plot common garden test under contrasting water regimes, with one plot maintained irrigated and the other one subjected to moderate summer water deficit. The six genotypes displayed a large range of xylem anatomy, mean vessel and fibre diameter varying from about 40 to 60 microm and from 7.5 to 10.5 microm, respectively. Decreased water availability resulted in a reduced cell size and an important rise in vessel density, but the extent of xylem plasticity was both genotype and trait dependent. Vessel diameter and theoretical xylem-specific hydraulic conductivity correlated positively with stomatal conductance, carbon isotope discrimination and growth performance-related traits and negatively with intrinsic WUE, especially under water deficit conditions. Vessel diameter and vessel density measured under water deficit conditions correlated with the relative losses in biomass production in response to water deprivation; this resulted from the fact that a more plastic xylem structure was generally accompanied by a larger loss in biomass production.

Modelled temperature-dependent excitability behaviour of a generalised human peripheral sensory nerve fibre

The objective of this study was to determine if a recently developed human Ranvier node model, which is based on a modified version of the Hodgkin-Huxley model, could predict the excitability behaviour in human peripheral sensory nerve fibres with diameters ranging from 5.0 to 15.0 microm. The Ranvier node model was extended to include a persistent sodium current and was incorporated into a generalised single cable nerve fibre model. Parameter temperature dependence was included. All calculations were performed in Matlab. Sensory nerve fibre excitability behaviour characteristics predicted by the new nerve fibre model at different temperatures and fibre diameters compared well with measured data. Absolute refractory periods deviated from measured data, while relative refractory periods were similar to measured data. Conduction velocities showed both fibre diameter and temperature dependence and were underestimated in fibres thinner than 12.5 microm. Calculated strength-duration time constants ranged from 128.5 to 183.0 micros at 37 degrees C over the studied nerve fibre diameter range, with chronaxie times about 30% shorter than strength-duration time constants. Chronaxie times exhibited temperature dependence, with values overestimated by a factor 5 at temperatures lower than body temperature. Possible explanations include the deviated absolute refractory period trend and inclusion of a nodal strangulation relationship.

Organic compatible polyacrylamide hydrogel fibers

Ultra-fine fibrous PAAm hydrogel membranes were fabricated by electrospinning of aqueous solutions, followed by reaction with glutaraldehyde. A wide range of fiber diameters (267 nm to 2.8 μm) and morphologies (beaded, round, branched and ribbon) could be achieved by PAAm molecular weight and solution properties. The optimally glutaraldehyde-crosslinked membranes were highly stable in water as well as in organic solvents (methanol, ethanol, acetone, chloroform, DMF and cyclohexane). Glutaraldehyde formed imine with PAAm amide side groups in the form of crosslinking bridges as well as grafts with hydrolyzed carboxylic end groups. The fibrous membrane showed excellent thermal stability, hydrophilicity, super water absorbency and exceptional tensile strength. The fibrous membrane exhibited excellent ability to entrap β-galactosidase enzyme while allowing efficient diffusion of the substrate from and released products into surrounding media. The dual organic solvent and aqueous media compatible fibrous membranes have the promise for solid supported catalysis and diagnostic as well as a wide range of biomedical and industrial applications.

Empirical model of the photon path length for a single fiber reflectance spectroscopy device

A reflectance spectroscopic device that utilizes a single fiber for both light delivery and collection has advantages over classical multi-fiber probes. This study presents a novel empirical relationship between the single fiber path length and the combined effect of both the absorption coefficient, mua (range: 0.1-6 mm-1), and the reduced scattering coefficient, micro's (range: 0.3 - 10 mm-1), for different anisotropy values (0.75 and 0.92), and is applicable to probes containing a wide range of fiber diameters (range: 200-2000 microm). The results indicate that the model is capable of accurately predicting the single fiber path length over a wide range (r = 0.995; range: 180-3940 microm) and predictions do not show bias as a function of either microa or micro's .

Approximation of motor unit structure from the analysis of motor unit potential

Objectives: The aim of this simulation study was to approximate certain features of motor unit structure on the basis of motor unit potential (MUP) analysis. Methods: The principle of the approximation method has been to invert the procedure used in the simulation of the MUP. An algorithm has been developed that analyses the recorded potential and estimates the number of fibers that contribute to the MUP, their diameters and localization relative to the electrode. These parameters have been determined by minimizing the differences between the recorded and modeled potentials. Results: The method has been tested on MUPs recorded in the muscles of healthy and diseased subjects. The evaluated range of fiber diameters and densities in a healthy muscle was consistent with its morphological characteristics. In pathological cases, the results of the analysis indicated changes of fiber diameters and densities typical of a given pathological process. Conclusion: Preliminary results of simulations suggest that the proposed method is a potentially useful tool for the approximation of morphological features of muscle fibers contributing to the MUP. Significance: The analysis of MUPs, in addition to the evaluation of the electrical activity of the muscle with the use of the proposed approximation method, may also permit characterization of muscle morphology, and therefore it may improve the diagnostic value of electromyography.

Fibronectin or chitosan addition to electrospun cellulose acetate scaffolds enhances endothelial cell infiltration

Our goal was to evaluate endothelial cell infiltration into electrospun cellulose acetate scaffolds, with a fiber diameter range of 1–5μm. Chitosan was added prior to electrospinning to increase scaffold stiffness. Fibronectin was added to formed scaffolds to add a specific ligand binding site for cell migration. Human umbilical vein endothelial cells (ECs) were cultured on glass for 1 day. After which, uv light sterilized scaffolds were placed on top of adherent ECs. EC viability, density and morphology on scaffolds and bare glass were investigated for 9 days after scaffold placement. ECs were found within all uv sterilized scaffolds after 1 day in culture. On pure cellulose acetate scaffolds, EC density plateaued on day 4 at a value approximately 50% of the cell density on paired glass. Cell density on scaffolds with chitosan or fibronectin increased continually over the 10 day culture, surpassing EC density on paired glass. Cell viability was high on all scaffolds and glass (>90%). With increased time in culture, the percentage of elongated ECs increased significantly on all scaffolds. ECs can migrate onto electrospun cellulose acetate scaffolds, showing a preference for a three dimensional matrix over two dimensional glass. Addition of chitosan or fibronectin to electrospun cellulose acetate scaffolds enhanced migration against gravity onto scaffolds and EC elongated morphology. Thanks to NIH HL55492.

Empirical model description of photon path length for differential path length spectroscopy: combined effect of scattering and absorption

Differential path length spectroscopy (DPS) is a method of reflectance spectroscopy that utilizes a specialized fiber geometry to make the photon path length (tau) insensitive to variations in tissue optical properties over a wide range of absorption (mu(a)) and total scattering (mu(s)) coefficients, which are common within the ultraviolet/visible (UV/VIS) wavelength region. This study extends the description of tau to larger mu(a) and smaller mu(s) values, optical properties that are representative of the near-infrared region (NIR), a region where the DPS path length may be dependent on both coefficients. This study presents a novel empirical relationship between tau and the combined effect of both mu(a) (range: 0.1-12 mm(-1)) and mu(s) (range: 1.5-42 mm(-1)), anisotropy of 0.8, and is applicable to DPS probes containing a wide range of fiber diameters (range: 100-1000 microm). The results indicate that the simple empirical formula, including only one fitted parameter, is capable of accurately predicting tau over a wide range (r=0.985; range: 80-940 microm) and predictions are not biased versus mu(a) or mu(s). This novel relationship is applicable to analysis of DPS measurements of tissue in both the UV/VIS and NIR wavelength regions and may provide information about the wavelength-specific tissue volume optically sampled during measurement.

Spectral behavior in thinned long period gratings: effects of fiber diameter on refractive index sensitivity

We report the experimental investigation of the sensitivity characteristics to the surrounding refractive index (SRI) in thinned long period gratings (LPGs) for a wide range of fiber diameters and different low-orders cladding modes. Wet chemical etching combined with microscopic and spectral analysis allow us to experimentally retrieve the SRI sensitivity characteristics of thinned LPGs. The obtained results allow us to identify accurately the dependence of the sensitivity characteristics on the fiber radius, taking into account the SRI range and the order mode. This provides a useful tool to identify the thinned structure able to fulfill the sensitivity requirements by maintaining an acceptable robustness level.

Evaluation of flax accessions for high value textile end uses

Due to recent changes in EC subsidies for flax cultivation it has been difficult to grow short fibre flax profitably in the UK. The Texflax project aimed to demonstrate that high quality flax fibre can be produced and processed on short fibre cotton spinning systems. Initially 92 flax accessions were cultivated on test sites in the UK over three growing seasons to explore the range of fibre diameter found in fibre flax. The efficacy of applying a translocating herbicide at different stages of plant maturity for optimum fine fibre production was explored. A range of factors indicated that application at the midpoint of flowering stage is favourable for the desiccation of flax and onset of retting. Fibre was caustic extracted using a laboratory method developed at De Montfort University, and fibre evaluated in terms of diameter, length, consistency and cleanliness. At the end of the project five accessions from the original 92 were chosen as producing optimal quality fibre suitable for high value textile end uses. Improved agronomy and subsequent processing enabled yarns with a 50:50 cotton:flax blend to be spun at 26 N m yarn count, the normal blend ratio for this count being 70:30. The yarn properties show an improvement when compared to standard products and finer quality fabrics have been prepared using the yarns.

Low-frequency magnetic susceptibility of fiber Fe-Cu composites

Magnetic properties of fiber Fe-Cu composites prepared by pack hydraulic pressing have been studied. The measurements of the low-frequency magnetic susceptibility have been performed on samples differing in the number and diameter of fibers of armco iron in the copper matrix. It has been established that in a certain range of fiber diameters the processes of deformation and annealing dramatically change the character of the susceptibility hysteresis loops in an external magnetic field. It has been shown that this change can be due to structural inhomogeneity of the fibers and, consequently, the inhomogeneity of their magnetic subsystem.

Structure–property relationships in glass reinforced polyamide, part 2: The effects of average fiber diameter and diameter distribution

AbstractWe present the results of an extensive study of the influence of average fiber diameter and the width of the diameter distribution on the performance of injection‐molded glass‐fiber reinforced polyamide 6,6. In the average fiber diameter range from 9 to 18 μm, dry‐as‐molded (DaM) composite unnotched impact and tensile strength decreased significantly. The composite notched impact performance and tensile modulus showed little dependence on fiber diameter. The influence of broadening the fiber diameter distribution by blending glass fiber samples of different average diameter was found to be particularly negative on the level of composite unnotched impact when compared at equal number average diameter. After hydrolysis treatment, the composite tensile strength and modulus exhibited a large drop compared to the DaM results. In contrast, the unnotched impact results became insensitive to fiber diameter after hydrolysis. The average level of unnotched impact after hydrolysis was sufficiently high to show an increase over DaM when the fiber diameter was above 14 μm. Residual fiber length correlated significantly with fiber diameter with a lower average length for thinner fibers. The interfacial shear strength was found to be in the range of 26–34 MPa for DaM composites. There was a highly significant inverse correlation between the DaM interfacial strength and the average fiber diameter. It is shown that results from both tensile and unnotched impact measurements can be brought back to single trend lines by using a Z average value for the average fiber diameter, which is more heavily weighted to the thicker fibers in the distribution. POLYM. COMPOS., 28:331–343, 2007. © 2007 Society of Plastics Engineers

A simulation of unsteady-state filtration via nanofiber media at reduced operating pressures

In this work, 3-D structures resembling nanofiber ( d f < 200 nm ) filter media are simulated and challenged with nanoparticle aerosols at reduced operating pressures. For the range of fiber diameters considered in this paper, the free molecular flow regime is dominant. Therefore, the disturbances to the air flow field caused by the fibers are neglected. Nanoparticle capture efficiency of nanofiber webs, due to Brownian diffusion and interception, is calculated for particle diameters ranging from 50 to 500 nm. Our simulations show that by decreasing the fiber diameter, the minimum collection efficiency of filtration media having identical pressure drops increases. This effect is accompanied by a decrease in the particle diameter associated with these minimum efficiencies—the most penetrating particle diameter. Moreover, it is demonstrated that increasing the flow temperature enhances the nanoparticle capture efficiency of nanofiber filters. Allowing the particles to deposit on the fibers as well as each other, the caking process of such nanofiber filters is simulated for different monodisperse and polydisperse aerosols at different temperatures. The statistical information regarding the composition of nanoparticle cakes formed at high and low temperatures is presented and discussed.

絹／ナイロン６６ブレンドナノファイバー集合体の摩擦特性

The silk fibroin/nylon 66 blended nanofiber webs were made by the electrospinning process and investigate the effect of blend ratio on the structure and surface properties of electrospun nanofiber assemblies. Tg of silk fibroin and nylon 66 blends in DSC curves shifted to that of nylon when the nylon content increased. With the increase of silk blend ratio, the decrease of the fiber diameter was observed. The mean coefficient of friction (MIU) was measured by KES surface tester. The obvious effect of fiber diameter on MIU was not found in the fiber diameter range of 50 to 270nm. Maximum values of MIU were observed for the silk/nylon blend ratio of 50/50%.