Interfiber Distance Research Articles

Remitted photon path lengths in human skin: in-vivo measurement data.

The remitted photon path lengths in human skin can be estimated by modelling; however, there are very few experimental data available to validate the simulations. This study exploited the photon time of flight method where picosecond laser pulses at seven wavelength bands in the spectral range 560-800 nm were launched into in-vivo forearm skin of 10 volunteers via an optical fiber. The pulses of back-scattered light were detected via another optical fiber placed at variable distance (1, 8, 12, 16 or 20 mm) from the input fiber, with subsequent analysis of their shapes for all 35 spectral-spatial combinations. Using a deconvolution algorithm, the distribution functions of remitted photon arrival times after infinitely narrow input pulse were calculated and transformed into distributions of skin-remitted photon path lengths. Nearly linear dependences of the remitted photon mean path length on inter-fiber distance were obtained for all wavelength bands, while the spectral dependences at fixed inter-fiber distances showed more complicated character, most probably due to absorption of the dermal hemoglobin.

Numerical simulation of solute removal from a cross-flow past a row of parallel hollow-fiber membranes

A multi-parametric simulation of the 2-D steady transverse flow of viscous incompressible fluid and diffusion transport of a dissolved solute past a model fibrous medium – a row of parallel sorbent fibers or hollow-fiber membranes is performed in a wide range of Schmidt (Sc) and Peclet (Pe) numbers for fiber Reynolds numbers up to Re = 100. The Navier-Stokes and convection-diffusion equations are solved numerically and the fiber capture efficiency for solute molecules is calculated as a function of Re, Sc and inter-fiber distance. The field of solute concentration and the fiber capture efficiency are found with zero concentration-fixed and diffusion flux boundary conditions set at the streamlined fiber surface, and the difference between the results of simulations with the two boundary conditions is shown for high Peclet numbers. It is also shown that the fiber capture efficiencies estimated with both boundary conditions tend to a constant maximum value for low Peclet numbers. The results of simulations for the fiber capture efficiency are validated by comparison with existing analytical asymptotic solutions for low and high Peclet numbers, and the agreement is shown.

Modified micro-mechanics based multiscale model for progressive failure prediction of 2D twill woven composites

To consider fiber random distribution at the microscale for the multiscale model based on the micro-mechanics failure (MMF) theory, clustering method is used for the extraction of amplification factors. As the clustering method is a kind of unsupervised machine learning method, the elements with similar mechanical behavior under external loading can be included in a cluster automatically at the microscale. With this modification, the fiber random distribution model can be used for multiscale damage analysis in the framework of MMF theory. To validate the modified multiscale analysis method, progressive damage analysis of a kind of 2D twill woven composites is conducted based on different microscale models. The stress values for microscale models with fiber hexagonal and random distribution patterns are compared first. Much higher stress concentration is generated in the fiber random distribution model due to the smaller inter-fiber distance especially under longitudinal shear loading. The obtained cluster distribution results exhibit the characters of the stress distribution in the two microscale models. Thereafter, tensile and compressive responses of the 2D twill woven composite are predicted with the modified multiscale analysis method and accuracy of the method is verified through comparison with published experimental results. From the simulation results, it can be found that the matrix damage initiation from the model based on the fiber random distribution model is premature compared with that from the model based on the fiber hexagonal distribution model. Besides, under tensile loading, the damage all initiates from the fill tows and propagates to the wrap tows. However, under compressive loading, the matrix damage initiates from the wrap tows in the model based on the fiber random distribution model.

A virtual experimental approach to evaluate transverse damage behavior of a unidirectional composite considering noncircular fiber cross-sections

This study investigated the transverse damage behavior of a unidirectional composite containing a complex microstructure having noncircular fiber cross-sections. For this purpose, a finite-element (FE) model based real microscopic images of the M55J/M18 composite was generated with the signed distance function (SDF) by the level-set method and the trimming mesh technique. In addition, the interphase zone was constructed along the interface between the fiber and the matrix. Subsequently, a virtual experiment simulating a three-point bending test was conducted with the generated FE model. Crack propagation analysis was carried out with the cohesive zone model (CZM) by applying transverse tension under plane strain condition. The crack length and propagation directions were compared to those of the three-point bending test. To make a nice correlation between the virtual experiment and actual experiment, the effects of the fiber shape, thermal residual stress, and various fracture toughnesses were investigated on the length and propagation direction of the cracks. It was found that, the fiber shape is vital to the inter-fiber distance and fiber volume fraction (Vf), which strengthen or weaken the stress concentration, thus making the propagation direction of the cracks warped and the length of cracks varied.

Transverse Young's modulus of carbon/glass hybrid fiber composites

Hybrid fiber composites offer designers a means of tailoring the stress–strain behavior of lightweight materials used in high-performance structures. While the longitudinal stress–strain behavior of unidirectional hybrid fiber composites has been thoroughly evaluated experimentally and analytically, relatively little information is available on the transverse behavior. The objective of the current investigation is to present data on the transverse modulus of elasticity of unidirectional composites with five different ratios of carbon and glass fiber and to compare the data with predictive and fitted models. The transverse modulus increases monotonically with the proportion of glass fiber in the composite. Finite element analysis was used to evaluate different ways to model voids in the matrix and allowed the unknown transverse properties of the carbon fibers to be backed out using experimental data from the all-carbon composite. The finite element results show that the transverse modulus can be accurately modeled if voids are modeled explicitly in the matrix region and if modulus is calculated based on stress applied along the minimum interfiber distance path between adjacent fibers arranged in a rectangular array. The transverse modulus was under-predicted by the iso-stress model and was well predicted by a modified iso-stress model and a modified Halpin–Tsai model.

Optimization of Process Parameters to Control Yarn Packing Density of Cotton Spun Yarn by Using Multiple Regression Models

Ring spinning frame is the most common and widely used technique for the production of yarn. This yarn subsequently utilized for the production of fabrics. Recently the research studies are more emphasis to create the living comfort condition. The yarn package density has a vital role to determine the feel, comfort, bulkiness and dyeing characteristics of the spun yarn. The yarn packaging density is largely influenced by the yarn process parameters. Ring spinning technique is the most common and widely used for the production of yarn. This yarn subsequently utilized for the production of fabrics. Recently the research studies are more emphasis to create the living comfort condition. The yarn package density is a vital role to determine the feel, comfort, bulkiness and dyeing characteristics of the spun yarn. It is largely influenced by the yarn manufacturing techniques and raw material used. The effects of spinning process parameters on packing density will be helpful to predetermine the yarn comfort behaviour prior to the complete the fabric manufacturing process. Mechanical behaviour of the staple yarn depends on the fiber characteristics and the yarn structure i.e. the arrangement of the individual fiber on the cross-section of the yarn. The fiber distribution on the cross section of the yarn and packing density of yarn has been investigated. The study provides how the spinning process parameters affect the internal structure of ring spun yarn. The aim of the study is to improve the package density of the yarn to achieve dynamometric and comfort properties of yarn to attract a wide variety of customers. Yarn Packing Density represents inter-fiber distance and friction, hence controlling the mechanical and comfort properties of the yarn. The main objective of this study is to control the packing density of yarn during the spinning process. In this work the 100 percent cotton used as raw material and spun on a ring spinning machine. The 135 ring yarns samples have been produced from three different types of yarn counts include (Ne 8, 16 and 24) with nine different samples of identical counts were produced. The three different variables within the count sample are TPI and spindle speed and count. Yarn packing density was calculated by using the driven equation by the application of multiple regression models. The final result shows that packing density has directly related to the TPI, Spindle speed and count

Optimization of Process Parameters to Control Yarn Packing Density of Cotton Spun Yarn by Using Multiple Regression Models

Ring spinning frame is the most common and widely used technique for the production of yarn. This yarn subsequently utilized for the production of fabrics. Recently the research studies are more emphasis to create the living comfort condition. The yarn package density has a vital role to determine the feel, comfort, bulkiness and dyeing characteristics of the spun yarn. The yarn packaging density is largely influenced by the yarn process parameters. Ring spinning technique is the most common and widely used for the production of yarn. This yarn subsequently utilized for the production of fabrics. Recently the research studies are more emphasis to create the living comfort condition. The yarn package density is a vital role to determine the feel, comfort, bulkiness and dyeing characteristics of the spun yarn. It is largely influenced by the yarn manufacturing techniques and raw material used. The effects of spinning process parameters on packing density will be helpful to predetermine the yarn comfort behaviour prior to the complete the fabric manufacturing process. Mechanical behaviour of the staple yarn depends on the fiber characteristics and the yarn structure i.e. the arrangement of the individual fiber on the cross-section of the yarn. The fiber distribution on the cross section of the yarn and packing density of yarn has been investigated. The study provides how the spinning process parameters affect the internal structure of ring spun yarn. The aim of the study is to improve the package density of the yarn to achieve dynamometric and comfort properties of yarn to attract a wide variety of customers. Yarn Packing Density represents inter-fiber distance and friction, hence controlling the mechanical and comfort properties of the yarn. The main objective of this study is to control the packing density of yarn during the spinning process. In this work the 100 percent cotton used as raw material and spun on a ring spinning machine. The 135 ring yarns samples have been produced from three different types of yarn counts include (Ne 8, 16 and 24) with nine different samples of identical counts were produced. The three different variables within the count sample are TPI and spindle speed and count. Yarn packing density was calculated by using the driven equation by the application of multiple regression models. The final result shows that packing density has directly related to the TPI, Spindle speed and count

Bubble collisions on parallel arranged fibers

We report an experimental and theoretical investigation of bubble collisions on parallel arranged fibers. Using high speed videography, we visualized the impact outcomes and classified them into three modes: capturing, single bubble rising, and splitting. The experimental results demonstrate that the impact mode is mainly determined by the distance between the fibers as well as the rising speed of the bubble. We present the results in a regime map, displaying the dependence of the impact outcomes on dimensionless parameters: Web = ρUb2D/σ, Bo = ρgD2/σ, and d/D in the range of 0 ≤ Web ≤ 25, 0.4 ≤ Bo ≤ 0.7, 0.30 ≤ d/D ≤ 0.75, where ρ is the liquid density, Ub is the collision speed of bubble, D is the bubble diameter, σ is the surface tension, g is the gravitational acceleration, and d is the inter-fiber distance. The observed regime boundaries are explained with scale analysis. We also examined the size of daughter bubbles for splitting cases, and the results unveil the critical dependence of the daughter bubble size on the impact offset rather than on the collision speed. The results are expected to be widely used to control bubble filtration or generation in a variety of engineering systems aimed at improving heat and mass transfer using bubbles.

A Fundamental Study of Charge Effects on Melt Electrowritten Polymer Fibers

Melt electrowriting (MEW) is an electrohydrodynamics (EHD)-based additive manufacturing paradigm for printing microscale fibers. Although models for charge transport during EHD printing have been described, significant challenges arise from the in-process charge dynamics in MEW process, which limits the achievable print resolution. This paper advances a methodology to analyze the effects of charge dynamics on the MEW-printed structure resolution. First, fibers printed with an oscillating toolpath exhibit two distinct alignment patterns with constituent fibers either successively overlapping along the toolpath or diverging into individual fibers without apparent overlap on conductive and non-conductive substrates, respectively, pointing to the existence of inter-fiber charge phenomena. Next, a set of straight fibers are printed on two types of substrates to investigate the relationship between the prescribed inter-fiber distance (set Sf) and measured Sf. Both repulsion (measured Sf > set Sf) and attraction (measured Sf < set Sf) are observed. Moreover, a mathematical model based on line-point charge interactions is advanced to explain the fiber attraction-repulsion phenomenon. Finally, residual charge measurements with a customized Faraday Cup reveal that printed scaffolds on conductive and non-conductive substrates are negatively and positively charged for residual charge, respectively.

Statistical analysis of composites reinforced with randomly distributed fibers using a meshless method

This paper adopts a meshless method that combines the moving least-squares approximation and Galerkin weak form to investigate the mechanical properties of unidirectional fiber-reinforced composites under a lateral load. The degree of nonuniformity is adopted to quantify the spatial distribution of randomness during simulation, and then the numerical implementation is developed to generate a representative volume element (RVE) model with random distribution of fibers. A statistical analysis is carried out by using three descriptors, that is, inter-fiber distance, second-order intensity function and radial distribution function. Numerical examples are presented to illustrate the accuracy of the proposed multiscale meshless method, and excellent agreement is achieved in comparison with experiments and the finite element method. Finally, the performance of the proposed numerical technique is evaluated by considering the effects of RVE size, node influence domain, degree of nonuniformity and fiber volume fraction separately.

Solvent-Induced Nanotopographies of Single Microfibers Regulate Cell Mechanotransduction.

The extracellular matrix (ECM) is a dynamic three-dimensional (3D) fibrous network, surrounding all cells in vivo. Fiber manufacturing techniques are employed to mimic the ECM but still lack the knowledge and methodology to produce single fibers approximating cell size with different surface topographies to study cell-material interactions. Using solvent-assisted spinning (SAS), the potential to continuously produce single microscale fibers with unlimited length, precise diameter, and specific surface topographies was demonstrated. By applying solvents with different solubilities and volatilities, fibers with smooth, grooved, and porous surface morphologies are produced. Due to their hierarchical structures, the porous fibers are the most hydrophobic, followed by the grooved and the smooth fibers. The fiber diameter is increased by increasing the polymer concentration or decreasing the collector rotational speed. Moreover, SAS offers the advantage to control the interfiber distance and angle to fabricate multilayered 3D constructs. This report shows for the first time that the micro- and nanoscale topographies of single fibers mechanically regulate cell behavior. Fibroblasts, grown on fibers with grooved topographical features, stretch and elongate more compared to smooth and porous fibers, whereas both porous and grooved fibers induce nuclear translocation of yes-associated protein. The presented technique, therefore, provides a unique platform to study the interaction between cells and single ECM-like fibers in a precise and reproducible manner, which is of great importance for new material developments in the field of tissue engineering.

Mathematical-model-guided development of full-thickness epidermal equivalent

Epidermal equivalents prepared with passaged keratinocytes are typically 10–20 μm thick, whereas intact human epidermis is up to 100 μm thick. Our established mathematical model of epidermal homeostasis predicted that the undulatory pattern of the papillary layer beneath the epidermis is a key determinant of epidermal thickness. Here, we tested this prediction by seeding human keratinocytes on polyester textiles with various fiber-structural patterns in culture dishes exposed to air, aiming to develop a more physiologically realistic epidermal model using passaged keratinocytes. Textile substrate with fiber thickness and inter-fiber distance matching the computer predictions afforded a three-dimensional epidermal-equivalent model with thick stratum corneum and intercellular lamellar lipid structure. The basal layer structure was similar to that of human papillary layer. Cells located around the textile fibers were proliferating, as indicated by BrdU and YAP (Yes-associated protein) staining and expression of melanoma-associated chondroitin sulfate proteoglycan. Filaggrin, loricrin, claudin 1 and ZO-1 were all appropriately expressed. Silencing of transcriptional coactivator YAP with siRNA disturbed construction of the three-dimensional structure. Measurement of trans-epidermal water loss (TEWL) indicated that the model has excellent barrier function. Our results support the idea that mathematical modeling of complex biological processes can have predictive ability and practical value.

Highly Conductive Polydimethylsiloxane/Carbon Nanofiber Composites for Flexible Sensor Applications

AbstractA polydimethylsiloxane (PDMS)/carbon nanofiber (CNF) nanocomposite with piezoresistive sensing function is presented. Excellent electrical conductivity is achieved by dispersing the CNFs into PDMS. A facile, low cost, and scalable fabrication procedure allows the sensors to be made in different shapes. The piezoresistive sensors show repeatable response up to 30% tensile strain. In addition, the characterization of sensing mechanism using an in situ mechanical testing system within a scanning electron microscope reveals the reorganization of CNF network by varying fiber alignment and interfiber distance in the nanocomposites under tensile load. To validate the wearable sensing capability, nanocomposite straps are employed to monitor the finger motions under various bending speed and holding time. Two different shapes of compressive sensors, including cylinder and truncated cone, are tested in compression strain as low as 3%, with gauge factors of 18.3 and 6.3, respectively. In addition, the sensing capability is independent of the applied strain rates and is highly repeatable in 1000 cycles under compression. Finally, the developed nanocomposites are made into sensor arrays for pressure sensing ranging from 35 to 690 kPa. The versatility and ease of fabrication of the reported nanocomposites can bridge the current challenge between performance and applicability of flexible sensors.

Influence of structural parameters at microscale on the fiber reinforcement

In this paper, a random configuration model for fiber arrangement is proposed and implemented in a computer code. This development enables the investigation of the effect of the random arrangements of the fibers inside the tow on the permeability and the flow properties. Four parameters are considered including three microstructural parameters: side length of the domain L, variation of radii Δ r, minimum interfiber distance δmin, and one macro parameter: porosity ɛ. Finite element method is performed for the transverse flow of porous media with random arrangements of fibers. Morris method for global sensitivity analysis is used to study the influence of four parameters. The results have shown that the porosity ɛ has the most obvious influence on the fiber reinforcement permeability.

Al-Coated Conductive Fiber Filters for High-Efficiency Electrostatic Filtration: Effects of Electrical and Fiber Structural Properties

Through the direct decomposition of an Al precursor ink AlH3{O(C4H9)2}, we fabricated an Al-coated conductive fiber filter for the efficient electrostatic removal of airborne particles (>99%) with a low pressure drop (~several Pascals). The effects of the electrical and structural properties of the filters were investigated in terms of collection efficiency, pressure drop, and particle deposition behavior. The collection efficiency did not show a significant correlation with the extent of electrical conductivity, as the filter is electrostatically charged by the metallic Al layers forming electrical networks throughout the fibers. Most of the charged particles were collected via surface filtration by Coulombic interactions; consequently, the filter thickness had little effect on the collection efficiency. Based on simulations of various fiber structures, we found that surface filtration can transition to depth filtration depending on the extent of interfiber distance. Therefore, the effects of structural characteristics on collection efficiency varied depending on the degree of the fiber packing density. This study will offer valuable information pertaining to the development of a conductive metal/polymer composite air filter for an energy-efficient and high-performance electrostatic filtration system.

Effects of inter-fiber spacing on fiber-matrix debond crack growth in unidirectional composites under transverse loading

The energy release rate (ERR) of a fiber–matrix debond crack in a unidirectional composite subjected to transverse tension is studied numerically. The focus of the study is the effect of the proximity of the neighboring fibers on the ERR. For this, a hexagonal pattern of fibers in the composite cross-section is considered. Assuming one fiber to be debonded at certain initial debond arc-length, the effect of the closeness of the surrounding six fibers on the ERR of the crack is studied with the inter-fiber distance as a parameter. Using an embedded cell consisting of discrete fibers in a matrix surrounded by the homogenized composite, a finite element model and the virtual crack closure technique are used to calculate the ERR. Results show that the presence of the local fiber cluster accelerates the crack growth up to a certain initial crack angle, beyond which the opposite effect occurs. It is also found that the residual stress due to thermal cooldown reduces the ERR. However, the thermal cooldown is found to enhance the debond growth in plies within a cross-ply laminate.

Hypoxia Inducible Factors Modify Collagen I Fibers in MDA-MB-231 Triple Negative Breast Cancer Xenografts

Hypoxia inducible factors (HIFs) are transcription factors that mediate the response of cells to hypoxia. HIFs have wide-ranging effects on metabolism, the tumor microenvironment (TME) and the extracellular matrix (ECM). Here we investigated the silencing effects of two of the three known isoforms, HIF-1α and HIF-2α, on collagen 1 (Col1) fibers, which form a major component of the ECM of tumors. Using a loss-of-function approach for HIF-1α or 2α or both HIF-1α and 2α, we identified a relationship between HIFs and Col1 fibers in MDA-MB-231 tumors. Tumors derived from MDA-MB-231 cells with HIF-1α or 2α or both HIF-1α and 2α silenced contained higher percent fiber volume and lower inter-fiber distance compared to tumors derived from empty vector MDA-MB-231 cells. Depending upon the type of silencing, we observed changes in Col1 degrading enzymes, and enzymes involved in Col1 synthesis and deposition. Additionally, a reduction in lysyl oxidase protein expression in HIF-down-regulated tumors suggests that more non-cross-linked fibers were present. Collectively these results identify the role of HIFs in modifying the ECM and the TME and provide new insights into the effects of hypoxia on the tumor ECM.

The effect of the structure of needle-punched nonwoven materials on their sorption capacity

The effect of the structure of needle-punched nonwoven materials on their sorption capacity during adsorption of liquids of different chemical natures is studied. The maximum sorption capacity is achieved at a certain volumetric density of the material, when the interfiber space is filled with liquids and depends on efficiency of formation of bundles of fibers oriented along the thickness of the web. The critical interfiber distance upon adsorption of a liquid depends on its surface tension.

Novel electrospun gas diffusion layers for polymer electrolyte membrane fuel cells: Part I. Fabrication, morphological characterization, and in situ performance

In this first of a series of two papers, we report an in-depth analysis of the impact of the gas diffusion layer (GDL) structure on the polymer electrolyte membrane (PEM) fuel cell performance through the use of custom GDLs fabricated in-house. Hydrophobic electrospun nanofibrous gas diffusion layers (eGDLs) are fabricated with controlled fibre diameter and alignment. The eGDLs are rendered hydrophobic through direct surface functionalization, and this molecular grafting is achieved in the absence of structural alteration. The fibre diameter, chemical composition, and electrical conductivity of the eGDL are characterized, and the impact of eGDL structure on fuel cell performance is analysed. We observe that the eGDL facilitates higher fuel cell power densities compared to a commercial GDL (Toray TGP-H-60) at highly humidified operating conditions. The ohmic resistance of the fuel cell is found to significantly increase with increasing inter-fiber distance. It is also observed that the addition of a hydrophobic treatment enhances membrane hydration, and fibres perpendicularly aligned to the channel direction may enhance the contact area between the catalyst layer and the GDL.

In vivo biocompatibility, vascularization, and incorporation of Integra® dermal regenerative template and flowable wound matrix.

Integra® matrix wound dressing (MWD) is used for the reconstruction of full-thickness skin defects. For the treatment of complex wounds, this dermal substitute is available as a flowable wound matrix (FWM) of identical composition. To clarify whether variations in sample preparation and consistency affect the biocompatibility and tissue incorporation, we herein compared MWD and FWM. The matrices were characterized using scanning electron microscopy and histology. Moreover, they were implanted in mouse dorsal skinfold chambers to analyze their in vivo performance over 2 weeks. Scanning electron microscopy showed a planar surface of MWD whereas FWM presented an irregular, fissured morphology. However, histology of the two matrices revealed an identical fiber thickness, fiber length, and interfiber distance. Repetitive stereo-microscopy and immunohistochemical analyses of MWD and FWM showed a comparable epithelialization of the implants in the dorsal skinfold chamber model. At day 14, both matrices exhibited a low collagen content and microvessel density. Moreover, they were infiltrated by a high number of myeloperoxidase (MPO)-positive neutrophilic granulocytes and a lower number of MAC387-positive macrophages and CD3-positive lymphocytes. These findings demonstrate that differences in preparation and consistency do not affect the tissue response to MWD and FWM, indicating a comparable regenerative capacity in wound healing. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 52-60, 2018.