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The behavior of the material against the external forces depends on its mechanical properties, including strength, elastic modulus, fatigue behavior, and so on. Of these properties, the elastic mod...

In tissue engineering, the structure of nanofibrous scaffolds and optimization of their properties play important role in the enhancement of cell growth and proliferation. Therefore, the basic idea of the current study is to find a proper method for tuning the extent of porosity of the scaffold, study the effect of porosity on the cell growth, and optimize the extent of porosity with the aim of achieving the maximum cell growth. To tune the scaffold’s porosity, four types of metal mesh with different mesh sizes were employed as collectors. For this purpose, the structural properties of polycaprolactone nanofibrous layers which were electrospun on collectors, and the level of neural A-172 cell growth on layers were investigated, and the results were compared with the results attained for the fabricated nanofibrous layer on a flat aluminum collector. It was found that upon changing the porosity of the metal mesh as collector, the fibers’ diameter would be inevitably changed, albeit insignificantly, and following no specific trends. However, changing the mesh size has shown a significant effect on the thickness and porosity of nanofibrous layer. According to the MTT assay results, the optimum neural cell growth was observed for the electrospun nanofibrous scaffold with the porosity of 96% and pore size of (0.42–23 µm) which has been fabricated on the type-4 collector having a mesh size of 10. The fabricated scaffold using this mesh with the optimum extent of porosity (58%) resulted in 44% enhancement in the cell growth as compared with the fabricated layer on the flat collector.

Application of electrospun nanofibrous scaffolds has received immense attention in tissue engineering. Fabrication of scaffolds with appropriate electrical properties plays a key role in neural tissue engineering. Since fibers orientation in the scaffolds affects the growth and proliferation of the cells, this study aimed to prepare aligned electrospun conductive nanofibers by mixing 1 %, 10 % and 18 % (w/v) doped polyaniline (PANI) with polycaprolactone (PCL)/poly lactic-coglycolic acid (PLGA) (25/75) solution through the electrospinning process. The fibers diameter, hydrophilicity and conductivity were measured. In addition, the shape and proliferation of the nerve cells seeded on fibers were evaluated by MTT cytotoxicity assay and scanning electron microscopy. The results revealed that the conductive nanofibrous scaffolds were appropriate substrates for the attachment and proliferation of nerve cells. The electrical stimulation enhanced neurite outgrowth compared to those PLGA/PCL/PANI scaffolds that were not subjected to electrical stimulation. As polyaniline ratio increases, electric stimulation through nanofibrous PLGA/PCL/PANI scaffolds results in cell proliferation enhancement. However, a raise more than 10 % in polyaniline will result in cell toxicity. It was concluded that conductive scaffolds with appropriate ratio of PANI along with electrical stimulation have potential applications in treatment of spinal cord injuries.

Surface friction of fabrics is one of the prominent tactile properties which influence the comfort and application of clothes. In this paper, a new approach is proposed to characterize the surface ...

The complex nature of spinal cord injuries has provided much inspiration for the design of novel biomaterials and scaffolds which are capable of stimulating neural tissue repair strategies. Recently, conductive polymers have gained much attention for improving the nerve regeneration. In our previous study, a three-dimensional (3D) structure with reliable performance was achieved for electrospun scaffolds. The main purpose in the current study is formation of electrical excitable 3D scaffolds by appending polyaniline (PANI) to biocompatible polymers. In this paper, an attempt was made to develop conductive nanofibrous scaffolds, which can simultaneously present both electrical and topographical cues to cells. By using a proper 3D structure, two kinds of conductive scaffolds are compared with a non-conductive scaffold. The 3D nanofibrous core-sheath scaffolds, which are conductive, were prepared with nanorough sheath and aligned core. Two different sheath polymers, including poly(lactic-co-glycolic acid) PLGA and PLGA/PANI, with identical PCL/PANI cores were fabricated. Nanofibers of PCL and PLGA blends with PANI have fiber diameters of 234±60.8 nm and 770±166.6 nm, and conductivity of 3.17×10-5 S/cm and 4.29×10-5 S/cm, respectively. The cell proliferation evaluation of nerve cells on these two conductive scaffolds and previous non-conductive scaffolds (PLGA) indicate that the first conductive scaffold (PCL/ PANI-PLGA) could be more effective for nerve tissue regeneration. Locomotor scores of grafted animals by developed scaffolds showed significant performance of non-conductive 3D scaffolds. Moreover, the animal studies indicated the ability of two new types of conductive scaffolds as spinal cord regeneration candidates.

In this paper, nylon 66/TiO2 composite nanofiber yarn has been developed using electrospinning method. The effect of the TiO2 nanoparticle content on the physical and tensile properties of the resulted composite nanofiber yarns has been extensively investigated using SEM, EDX, FTIR and mechanical testing machine. The probability density function is computed to model the diameter distribution of nanofibers constituent of the composite yarn for different percentages of TiO2. The addition of TiO2 nanoparticles into the electrospun composite nanofiber yarn decreases its tensile strength. The influence of thickness (diameter) and twist of the yarn on its tensile strength has been considered and the optimum conditions with improved tensile strength have been presented. Photoactivity of the composite yarns is tested against Rhodamine B (RhB). Results show that nanocomposite yarns are effective to be used as an economically and environmentally friendly photocatalyst in water remediation processes. They are not dispersed in the solution and can be removed easily without additional and costly steps of filtration or centrifuge.

Nanotopography and stiffness are major physical cues affecting cell fate. However, the current nanofiber modifications techniques are limited by their ability to control these two physical cues irrespective of each other without changing the materials' surface chemistry. For this reason, the isolated effects of topography and stiffness on osteogenic regulation in electrospun nanofibers have been studied incompletely. Here, we investigated 1. how functionalized multiwall carbon nanotubes (F-MWCNTs) loaded in Polycaprolactone (PCL) nanofibers control their physical properties and 2. whether the resulting unique structures lead to distinctive phenotypes in bone progenitor cells. Changes in material properties were measured by high-resolution electron microscopes, protein adsorption and tensile tests. The effect of the developed structures on human mesenchymal stem cell (MSC) osteogenic differentiation was determined by extensive quantification of early and late osteogenic marker genes. It was found that F-MWCNT loading was an effective method to independently control the PCL nanofiber surface nanoroughness or stiffness, depending on the applied F-MWCNT concentration. Collectively, this suggests that stiffness and topography activate distinct osteogenic signaling pathway. The current strategy can help our further understanding of the mechano-biological responses in osteoprogenitor cells, which could ultimately lead to improved design of bone substitute biomaterials.

Today nanofibers are used widely in a variety of applications. Among many investigations of nanofiber characteristics, their color features have been studied scarcely. In this study, nanofiber yarns were colored using two different methods: exhaustion dyeing and colored solution electrospinning or dope dyeing. In the first method, nylon66 nanofiber yarns were produced and then dyeing process was followed at different dye concentrations. In the second method, colored nanofiber yarns were produced directly using the yarn electrospinning setup. Through the spectrophotometric measurements, it was illustrated that the color saturation increases by increasing the dye content in the dyeing bath and electrospinning colored solution. At the end, the nanofiber yarns with equal dye content were produced using two mentioned methods. It was observed that the color strength of dope-dyed samples was lower than the dyeing process samples, but their levelness was better than the samples of dyeing process. Chromatic values...

Achieving whiteness and opaqueness has been an issue in paint, ceramic, paper, and coating industries from the very beginning. In the past two decades, biomimetics, for the construction of bio-inspired functional materials, has attracted much attention. As an application of biomimetic science, various structural colored materials are investigated by many researchers. The white beetle exoskeletal scales is one of those materials that shows a brilliant white color caused by randomly arranged chitin nanofibers. This material is the inspiration for achieving light weight, efficient, and low-cost white coatings by means of a nanostructure. We used this idea in this research to apply nanofibrous polymeric layer on a substrate, paper sheet in here, and witnessed the possible achievements by varying the nanofiber layer characteristics that underpin its optical properties. We coated nylon and PAN nanofiber layers on the surface of a paper using an electrospinning method and for both polymers desirably high whiteness and opaqueness achieved. Moreover, it was observed that end-use application in printing and writing is easily attained on the nanofiber-coated paper using the common methods. Measuring the properties of the nylon nanofiber-coated paper showed that the tensile strength and hydrophilicity slightly increased depending on the nanofiber layer characteristics.

In this paper, a new approach is proposed for characterizing the surface roughness of woven fabrics. This approach is based on the fringe projection moire techniques and analysis of the moire pattern, which is caused by the interaction between the Ronchi grating and the periodic structure of a woven fabric. In this study, an image processing procedure was employed and a new parameter called the “roughness index” was defined for quantifying the surface roughness. The results obtained from the moire technique were validated by a set of pair-comparison subjective tests. The proper correlation, with an average R-squared value of 0.9087, between subjective and objective tests confirmed the accuracy, correctness and efficiency of the new method. Statistical analysis of the roughness results clarified that the effect of fabric structural parameters such as the weave structure and weft density is significant in the confidence range of 95%.

In this study, a new approach is proposed to represent a model for heat transfer through a fabric containing microcapsules of phase change materials (micro-PCM). It is observed that the phase change phenomenon occurs within a melting temperature zone where the temperature is not constant. Based on this fact, during phase change process, the heat capacity of fabric which is comprised of constant and temperature dependent elements is changed. A variation function extracted from DSC results is applied to calculate the temperature dependent heat capacity of fabric. The model is applied to study the transient effect of PCM on a simulated skin temperature system once subjected to abrupt changes in environmental conditions from warm to cold. The values of Tmean are 0 and 4.6 for sample without PCM and sample containing maximum PCM with nominal melting point of 28 °C, respectively. |GT| are 32.51 and 139.2 for corresponding samples. The model was further verified by the effect of PCMs existence and PCM type on the temperature response of simulated skin.

Considering the efficient TiO 2 structure on enhancing its photocatalytic behavior is of great interest in recent years. Meanwhile, inhibiting the filtration process for detachment of the catalyst from the purified solution is very advantages. To approach this purpose, TiO 2 nanofiber yarns were successfully fabricated through the electrospinning technique using two oppositely charged nozzles followed by the calcinations process from a solution containing titanium precursor and polyvinyl acetate (PVAc) as the supporting material. The introduced nanofiber yarns eliminate the ultrasonic and centrifuge steps required in photocatalytic tests of nanoparticles and electrospun nanofibers. The results show that this new catalyst's structure maintains its shape during the photocatalytic degradation process and can be easily removed from the purified water.

Electrospun nanofiber matrices are widely used as scaffolds for the regeneration of different tissues due to similarities with fibrous components of the extracellular matrix. These scaffolds could act as a substrate for inducing mechanical stimuli to cells. The main mechanical stimuli factor in nanofiber scaffolds for determining the cell behaviors is stiffness of single nanofibers. This paper especially highlights the finding that the young's modulus of single nanofibers can be obtained from aligned nanofibers matrix. It is assume that, the modulus of single nanofibers are equal to modulus of completely aligned nanofibers. However, due to difficulty of producing completely aligned nanofibers, the obtained modulus of single nanofiber wouldn’t have significant value. Therefore, we propose a new mathematical model to predict the stiffness of single nanofibers from non-perfectly aligned nanofibers matrix.

Nanomedicine is a growing research area dealing with the engineering of materials at a nanometer scale for the improvement of treatment, diagnosis, and imaging of diseases. In medicine and therapeutic applications, the use of nanostructures, such as nanofibrous materials and nanoparticles as drug-delivery systems has improved the bioavailability, intestinal absorption, solubility, sustained and on-demand drug release and targeted delivery, and, more importantly, therapeutic effectiveness of anticancer agents. The expansion of novel nanoparticles and nanofibrous structures for targeted drug delivery is an exciting and challenging research field, in particular for the delivery of emerging cancer therapies. Electrospinning, as an interesting producing approach for nanostructures, is a straightforward and robust method to fabricate nanofibers with the potential to incorporate drugs and therapies agents in a simple and reproducible process. In addition, a broad range of drugs, from antibiotics and anticancer agents to proteins, aptamer, DNA, and RNA, have been incorporated into electrospun fibers. This chapter emphasizes on an emerging area using the electrospinning technique to generate biomimetic nanofibers and nanoparticles as drug delivery devices that are responsive to different stimuli, such as temperature, pH, light, and the electric/magnetic field for controlled release of therapeutic substances. In addition, the promising use of electrospun nanofibers and nanoparticles with extracellular matrix morphology and intrinsically guiding cellular drug uptake, which will be highly desired to translate the promise of drug delivery for clinical success, is scrutinized for different treatment strategies.

In this work, a dynamic system has been developed to evaluate the thermal behavior of fibrous layers containing PCM 1 . The system is able to concurrently resemble the triple condition of ‘human body–clothing layers–environment’. The system hotplate, acting as the metabolic heat generator of human body, is able to self-adjust depending on the activity level of body section. An adjustable layering unit has been placed on the hotplate to simulate clothing layers. The environmental condition was rapidly changed from 0 to beyond 60 °C and from 5 to 100% relative humidity in order to prepare a transient condition. On-line data acquisition software has been designed to record and monitor data of the upper hotplate (skin) and spaces between the fibrous layers. Two indices were introduced and extracted to represent the thermal behavior of body skin/layers in the presence of PCMs at different environments. The system was further verified by studying the effect of PCMs presence and their increase on the thermal behavior of body skin/fibrous layers. The effect of PCMs’ melting point, during thermal transient, was finally presented by the system.

The different aspects of fabricating continuous TiO2 nanofiber yarns using oppositely charged metallic nozzles are studied. The importance of a proper auxiliary polymer, solvent and process required for continuous yarn formation are considered as effective process factors and are studied. Practical studies on solution concentration of the proposed polymer and solvent showed that it plays a significant role in the continuous electrospinning of nanofiber yarns and the diameter of nanofibers contained in the yarns.

The demand for novel antibiotic-loaded electrospun nanofibrous structures has increased extremely in the recent years and has engaged the interests of scientists and engineers into a blend configuration of antibiotic drug and biocompatible polymers due to their unique applications in future of better therapeutic effect, reduced toxicity and sustained local antibiotic release over a period of time. One method to produce these antibiotic-loaded networks is by electrospinning process. However, it is very important to know structural characteristics and morphology of nanofibers for controlling the performance of the yields. In this paper, fabrication of electrospun nanofibers suited for antibiotic delivery system is investigated based on tetracycline hydrochloride as the antibiotic drug and poly (lactic-co-glycolic acid) as the biodegradable polymeric matrix. Furthermore, the effect of material and process parameters on morphology and release behavior of produced nonwovens is investigated. The efficacy of the medicated scaffolds using a static system for bacterial growth on agar plates was also proved.

Scaffold design has a critical role in tissue engineering as scaffold features affect cell attachment and proliferation. Size scale similarities of electrospun nano-/microfibrous scaffolds with a native extracellular matrix have been appealing for tissue engineering applications and numerous studies have investigated the effect of different aspects of nano-/microfibrous scaffolds such as fiber diameter, thickness of nano-/microfibrous scaffolds on cell behavior. In this study, electrospun poly (ϵ-caprolactone) (PCL) microfibrous scaffolds were fabricated with nanosized pores on the surfaces of fibers created by the electrospinning of PCL solution with a highly volatile solvent in a humid ambient and the effects of nanopores on the attachment and proliferation of epithelial kidney cells (Vero) and mesenchymal stem cells (MSCs) were investigated. Morphology and hydrophilicity of the scaffolds were analyzed by scanning electron microscopy (SEM) and the video contact angle system and evaluation of cells proli...

In this paper changes in the appearance of 100% cotton ring spun yarns due to several yarn-to-yarn abrasion cycles before rupture are characterized. Different pictorial indexes for four different yarn counts are evaluated. The process of abraded yarns is defined by image processing techniques. The comparison between the indexes found that the weight loss of yarns at each step is performed using linear regression analysis to introduce the most appropriate index for quantifying the yarns’ abrasion. The mean value of diameter index which is related to the changes in yarn core shows the highest correlation with weight loss. This method enables studying the yarn-to-yarn abrasion behavior before rupture more accurately and rapidly for quality control purposes.

Since spinal cord injury is a complicated problem, neural tissue repair, and regeneration strategies have received a great deal of attention. In this study, a three-dimensional (3D) nanofibrous core-sheath scaffold with nanorough sheath and aligned core were fabricated by a combined electrospinning method with water vortex and two-nozzle system. In vitro and in vivo biological tests were carried out on the poly(lactic-co-glycolic acid) (PLGA) scaffolds. The cell morphology and proliferation evaluation of nerve cells on 3D PLGA scaffolds were studied. Cells were properly orientated along the aligned fiber direction of the scaffold. In animal studies, adult rats received a complete lateral hemisection at the T9-T10 level. Scaffolds were engrafted to bridge 3 mm defects of 10 adult rat spinal cords; 10 rats were used as controls. For 8 weeks, motor and sensory recovery by open field locomotor scale, narrow beam and tail flick tests were assessed. Locomotor and sensory scores of grafted animals were significantly better than the control group. Histological findings demonstrated that the scaffold supports the axonal regeneration of injured spinal cords and regenerating axons were seen to enter the graft and extend along its length.

Electrospinning has been recognized as an efficient technique for the fabrication of neural tissue engineering scaffolds. Many approaches have been developed on material optimization, electrospinning techniques, and physical properties of scaffolds to produce a suitable scaffold for tissue engineering aspects. In this study, structural properties of scaffolds were promoted by controlling the speed of fiber collection without any post-processing. PLGA scaffolds, in two significantly different solution concentrations, were fabricated by the electrospinning process to produce scaffolds with the optimum nerve cell growth in a desired direction. The minimum, intermediate and maximum rate of fiber collection (0.4, 2.4, 4.8 m/s) formed Random, Aligned and Drown-aligned fibers, with various porosities and hydrophilicities. The scaffolds were characterized by fiber diameter, porosity, water contact angle and morphology. Human nerve cells were cultured on fiber substrates for seven days to study the effects of different scaffold structures on cell morphology and proliferation, simultaneously. The results of MTT assay, the morphology of cells and scaffold characterization recommend that the best structure to promote cell direction, morphology and proliferation is accessible in an optimized hydrophilicity and porosity of scaffolds, which was obtained at the collector linear speed of 2.4 m/s.

Fabrication of core–shell nanofibers by coaxial electrospinning system suited for drug delivery applications was investigated based on tetracycline hydrochloride (TCH) as the core and poly(lactide-co-glycolide) as the shell materials. Comparison of drug release from monolithic fibers (blend electrospinning) and core–shell structures was performed to evaluate the efficacy of the core–shell morphology. The nanofibrous webs are potentially interesting for wound healing purposes since they can be maintained for an adequate length of time to gradually disinfect a local area without the need of bandage renewal. Further, our studies showed the potential of core–shell nanostructures for sustained drug release, which also suppressed the burst release effect from 62 to 44% in the first 3 hours by adding only 1 wt% TCH to the polymeric shell. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers

This paper reports a fast, accurate, and non-destructive three-dimensional imaging approach based on using quantum dots and confocal laser scanning microscopy to get three-dimensional images of internal pore structure of the nanofibrous materials. A practical method of making the fiber fluorescent using quantum dots was applied before three-dimensional imaging by confocal laser scanning microscopy. Fibrous scaffolds with different porosity parameters produced by electrospinning and their three-dimensional pore structure was evaluated by this approach. Furthermore, the introduced approach can be used to measure the pore interconnectivity of the scaffold.

Specific internal pore architectures are required to provide the needed biological and biophysical functions for fibrous scaffolds as these architectures are critical to cell infiltration and in-grows performance. However, the key challenging on evaluating 3D pore structure of fibrous scaffolds for better understanding the capability of different structures for biological application is not well investigated. This article reports a fast, accurate, nondestructive, and comprehensive evaluation approach based on confocal laser scanning microscopy (CLSM) and three-dimensional image analysis to study the pore structure and porosity parameters of Nano/Microfibrous scaffolds. Also a new method of making the fiber fluorescent using quantum dots (QDs) was applied before 3D imaging. Fibrous scaffolds with different porosity parameters produced by electrospinning and their 3D-pore structure was evaluated by this approach and the results were compared to results of capillary flow porometry. The pore structural properties measured in this approach are in good agreement with that measured by the capillary flow porometry (with significant level 0.05). Furthermore, the introduced approach can measure the pore interconnectivity of the scaffold. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 101A: 765–774, 2013.

Layered fabric systems with an electrospun nanofiber web layered onto a sandwich of woven fabric were developed to examine the feasibility of developing breathable barrier textile materials. Some parameters of nanofiber mats, including the time of electrospinning and the polymer solution concentration, were designed to change and barrier properties of specimens were compared. Air permeability, water vapor transmission, and water repellency (Bundesmann and hydrostatic pressure tests) were assessed as indications of comfort and barrier performance of different samples. These performances of layered nanofiber fabrics were compared with a well-known water repellent breathable multi-layered fabric (Gortex). Multi-layered electrospun nanofiber mats equipped fabric (MENMEF) showed better performance in windproof property than Gortex fabric. Also, water vapor permeability of MENMEF was in a range of normal woven sport and work clothing. Comparisons of barrier properties of MENMEF and the currently available PTFE coated materials showed that, those properties could be achieved by layered fabric systems with electrospun nanofiber mats.

A new technology based on the liquid support system is introduced for fabricating continuous twisted nanofibrous yarn. In this novel technique, the electrospun yarn was collected from the top of the water vortex such that it can be twisted simultaneously during yarn production. Our study demonstrated the feasibility of the technique for producing continuous twisted yarn from well aligned nanofibers. It is shown that the system can be modified to have different yarn counts with various twists. Further, significant improvement can be seen in the strength and strain when nanofibrous yarn is twisted compared to non-twisted yarn. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers

This study presents an analytical model to calculate the residual velocity of projectile-penetrating targets composed of planar plain-woven fabric. A non-linear, explicit, three-dimensional finite-element code in ABAQUS 6.4 software is used to simulate the response of plain-woven fabric under high-speed projectile impact. This model is based on single yarn as a backbone component for discritisation. Yarns are modelled as shell elements with elastic behaviour. Non-uniform mesh size is used to achieve computational efficiency and to capture the details of deformation. Interaction between the projectile and the fabric, and between the yarns themselves, considering friction, was determined. Finally, results are compared with other researchers' experimental work to verify the model. Acceptable correlation between results of simulation and experiment is demonstrated in terms of both deformation and residual velocity. The predictive capability and the computational efficiency of the model are quite good.

This research has attempted to present a novel definition for apparent quality of weft knitted fabrics and their used yarns using the image analysis method and linear functions, which are calculated by neural networks. First, standard boards of yarn were analyzed using the image analysis method and artificial neural networks. Then, samples of plain, cross-miss and plain pique fabrics and their used yarns were tested for appearance. The results show that the correlation between apparent quality of knitted fabrics and their yarns is very strong. The ANOVA test confirmed that there is a strong influence of yarn type and fabric structure on fabric apparent quality. Although the yarn type has a strong effect on fabric appearance, the effect of fabric structure on its appearance is not remarkable. Other results show that the quality of the knitted fabric depends on the features of the raw materials and the effects of different knit elements.

Release profile of drug constituent encapsulated in electrospun core-shell nanofibrous mats was modeled by Peppas equation and artificial neural network. Core-shell fibers were fabricated by co-axial electrospinning process using tetracycline hydrochloride (TCH) as the core and poly(l-lactide-co-glycolide) (PLGA) or polycaprolactone (PCL) as the shell materials. The density and hydrophilicity of the shell polymers, feed rates and concentrations of core and shell phases, the contribution of TCH in core material and electrical field were the parameters fed to the perceptron network to predict Peppas constants in order to derive release pattern. This study demonstrated the viability of the prediction tool in determining drug release profile of electrospun core-shell nanofibrous scaffolds.

Electrospinning process can fabricate nanomaterials with unique nanostructures for potential biomedical and environmental applications. However, the prediction and, consequently, the control of the porous structure of these materials has been impractical due to the complexity of the electrospinning process. In this research, a theoretical model for characterizing the porous structure of the electrospun nanofibrous network has been developed by combining the stochastic and stereological probability approaches. From consideration of number of fiber-to-fiber contacts in an electrospun nanofibrous assembly, geometrical and statistical theory relating morphological and structural parameters of the network to the characteristic dimensions of interfibers pores is provided. It has been shown that these properties are strongly influenced by the fiber diameter, porosity, and thickness of assembly. It is also demonstrated that at a given network porosity, increasing fiber diameter and thickness of the network reduces the characteristic dimensions of pores. It is also discussed that the role of fiber diameter and number of the layer in the assembly is dominant in controlling the pore size distribution of the networks. The theory has been validated experimentally and results compared with the existing theory to predict the pore size distribution of nanofiber mats. It is believed that the presented theory for estimation of pore size distribution is more realistic and useful for further studies of multilayer random nanofibrous assemblies.

The color stability of resin cements plays a major role in the esthetic performance of porcelain laminate veneers. Some dual-polymerizable resin cements used to bond porcelain laminates were shown to undergo color changes during service. Some recently produced cements are described as being color stable, but scientific data are not available.The current study evaluated the effect of accelerated aging on the color and opacity of resin cements. The hypothesis was that the auto-polymerizing cements would show less color and opacity stability.Forty (0.7 x 18 mm) feldspathic porcelain disks were prepared and divided into four equal groups. The resin cements were bonded to the disks by application of an identical load of 2.5 kilograms, and they were polymerized according to the manufacturer's instructions. The groups were: Variolink Veneer (light-polymerizing), Variolink II (light-polymerizing), Variolink II (dual-polymerizing) and Multilink (auto-polymerizing). A spectrophotometer was used to measure the following color parameters in the CIE L*a*b* color space on a black and white background: deltaa*, deltab*, deltaL*, deltaC, deltaH, deltaE and deltaCR (contrast ratio). The measurements were performed before and after aging. Paired t- and one-way ANOVA tests were used to analyze the data (alpha = .05).None of the groups showed significant differences in deltaE before and after aging (p.05); deltaE remained in the range of clinical acceptance (deltaE3.3). All of the cements became more opaque, while deltaCR (difference in contrast ratio) was significantly different (p = .004). The auto-polymerized cement showed an increase in opacity.The studied cements behaved acceptably according to deltaE, but they became more opaque after aging.The studied cements can ensure color stability when used to cement porcelain laminate veneers, but the change in opacity can affect clinical results. Auto polymerizing cements become more opaque with aging; therefore, porcelain restorations may lose their match with other teeth.

The frictional property of woven fabrics is one of the prominent surface characteristics which influence the performance of fabrics in a variety of applications. In this paper a novel methodology and instrument is proposed to measure the tactile force between fabric and simulated skin in different directions, and the obtained data are used for assessing fabric frictional property. In this regard, nine groups of woven fabrics consisting of three weave structures and three different weft densities were tested. By fitting the data with a proper equation, the tactile force in terms of fabric direction was predicted. The mentioned equation is also utilized for estimation of frictional behavior of fabric in various directions. Moreover, a single, new parameter called “frictional energy” is defined which has the ability to properly quantify the fabric frictional behavior. Statistical analysis of results reveals that the effect of weave structure and weft density is significant on the fabric friction. Being aware of the effect of fabric construction on friction is a guide for selecting the suitable fabric for various end uses.

The false twist texturing method is one of the most common texturing techniques. This process depends on parameters such as tension, twist, and heater temperature. As false-twist texturing is a process which includes close interactions between machine working parameters and textured yarn properties, the effect of process parameters on yarn properties have been widely investigated. In this study the effect of first heater temperature, setting overfeed, and D/Y on the tenacity of set yarns and the effect of twist, texturing speed, and first heater temperature on crimp stability of stretch yarns are predicted using artificial neural network methodology.

Many kinds of pressure garments are currently used for various applications, such as treating of hypertrophic scars, reversing the effect of shock on the body's blood distribution, improving energy saving for athletes and enhancing the aesthetic appearance of the wearer. In order to design the desired pressure garments, predicting the amount of pressure is mandatory. Although many researchers have used the Laplace law as the prediction equation, there has been some discrepancy between predicted and experimental measured pressures. In this study, we focused on one of the parameters which influence this discrepancy. To predict the pressure by this law, the induced tension in the material is measured by a tensile strength device, and then is inserted into the equation while the real tension is induced by extending on curvature shape. We measured the tension induced in the rubber band, which was extended on a cylindrical surface by using a new tensile test assembly. Subsequently, this tension was compared with the tension induced in the flat geometry which is commonly used. The results show that there is a significant difference between the tension in the curvature and flat geometry.

A theoretical analysis is presented for the estimation of the number of contacts between fibers in random multilayer nanofibrous assemblies with arbitrary fiber diameter and orientation. The statistics of fiber contacts for single-layer nanofiber mats were considered first, and the equations were developed for three-dimensional multilayer nanofibrous assemblies by considering the superposition of the single-layer assemblies. Based on the theoretical approach presented here for multilayer nanofibrous networks, the network porosity, mean fiber diameter and a function of fiber aspect ratio contribute to a model to determine the average number of fiber contacts per unit fiber length in multilayer nanofibrous mats.The theory is studied parametrically and results compared with the work of a model presented by Samson. It is shown that the presented model compared to the existing models is more sensitive with the fiber diameter in the nano-scale. It is also believed that the presented theory for fiber-to-fiber co...

The extensive application in future of nano webs has attracted world tendency toward them. The identification of nano webs' characteristics can direct consumer toward their end uses. Many nano web characteristics depend on its structure. Since they are made of nano fibres and have thin structure, conventional optical techniques are not completely applicable to measure their structural properties. This paper will discuss the development of image analysis algorithms to measure and evaluate structural and morphological characteristics of nano web images including fibre properties (such as fibre orientation distribution, fibre diameter), pore properties (such as pore size and shapes) and web properties (such as web uniformity and fibre intersections). The results show that the method is capable of characterising real nano coated webs.

Fiber reinforced polymer structures typically respond very poorly to transverse impact events. In this study, some experimental investigations are performed on the low velocity impact behavior of unidirectional hollow, solid and hybrid (hollow/solid) polyester fiber composites. The materials are fabricated in a curved shape using filament winding method. The impact tests are applied on the simply supported specimens by a drop weight impact test apparatus at five levels of energy. To present a proper comparison on the results, the various densities of the materials are considered as normalizing coefficients. It is observed that in the hollow fiber composites cracks appear at an appreciably higher amount (93%) of impact energy than the solid ones.

In this paper, various three-dimensional (3D) nanofibrous structures were constructed based on liquid support systems and alteration of the solution charge property. Structures fabricated from the liquid support system include a nanofibrous ring and spindle-shaped nanofibrous ones. The ease of fabricating fluffy, randomly organized nanofibrous structure by altering the charge capacity of the electrospun solution is also demonstrated. The set-up conditions for the design of the nanofibrous structures using these techniques are discussed.