Mechanical Properties Of Single Fibers Research Articles

Direct measurement of human skeletal muscle specific tension and fiber length

Skeletal muscle’s isometric contractile properties are one of the classic structure-function relationships in all of physiology allowing for extrapolation of single fiber mechanical properties to whole muscle properties based on the muscle’s optimal fiber length and physiological cross-sectional area (PCSA). However, this relationship has only been validated in small animals and then extrapolated to human muscles which are much larger in terms of length and PCSA. We leveraged a unique surgical technique in which an intact, living, human gracilis muscle is transferred from the thigh to the arm, restoring elbow flexion after brachial plexus injury. During this surgery we directly measured subject specific gracilis muscle force-length relationship in situ and properties ex vivo. We hypothesized that the human gracilis would have a functional fiber length of about 23 cm, based on the anatomical literature, and a specific tension of 225 kPa, based on the physiological literature. Data are provided as mean±standard deviation of the mean. Twelve subjects (7 males, average age 54±12 years). In situ passive and active tension were directly measured using a buckle force transducer (BFT) placed on the distal gracilis tendon. Passive tension was measured in each of four joint configurations (JC) prior to muscle stimulation, and, to produce active tension, the anterior branch of the obturator nerve was stimulated. The muscle was progressively lengthened by extending the knee and abducting the hip. Since we could not measure optimal fiber length directly in our subjects during isometric testing we used a functional surrogate for optimal fiber length, the full-width at half-maximum (FWHM) defined from their force vs. length relationship. The FWHM is the width of the active force vs. muscle length curve at half the maximum force. A linear relationship between FWHM and optimal fiber length has been established across several mammalian species and muscles. Thus, to calculate FWHM, we fit each patient’s calculated fully active force vs. muscle length data to a quadratic curve and then calculated width at half the calculated maximum force from the equation. Optimal fiber length was then calculated from the previously established linear relationship between FWHM and optimal fiber length. Each subject’s PCSA was calculated from their muscle volume and optimal fiber length.From these experimental data we established a human muscle fiber-specific tension of 171±84 kPa (n=12). We also determined the average gracilis optimal fiber length was 12.9±3.3 cm (n=12). Surprisingly, these fiber lengths were about half of the previously reported optimal fascicle lengths of 23 cm. Thus, the long gracilis muscle appears to be composed of relatively short fibers acting in parallel that may not have been appreciated based on traditional anatomical methods. We thus suggest that the value of 171 kPa be considered the best current estimate of human muscle specific tension. This work was supported the Department of Veterans Affairs grant 1 I01 RX002462 and, in part, by Research Career Scientist Award Number IK6 RX003351 from the United States (U.S.) Department of Veterans Affairs Rehabilitation R&D (Rehab RD) Service. Pilot projects leading to this protocol were supported by the Shirley Ryan AbilityLab Catalyst Grant Program, National Science Foundation Graduate Research Fellowship under Grant No. 1255833 and the Mayo Clinic Graduate School. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Platen parallelism significance and control in single fiber transverse compression tests

Transverse compression tests are the established way to identify the transverse mechanical properties of single fibers. However, to the authors knowledge, the influence of an angle between the two compression platens has never been studied or quantified. In this paper, the importance of platen parallelism is studied for the first time through: numerical simulation and experimental investigation. A sensitivity analysis complements these studies by highlighting the importance of contact geometry in the analytical model, used in the inverse identification of the fiber’s apparent transverse elastic modulus ET. Experimental results show that a misalignment of 1° between the platens produces a variation of more than 35% on the identified ET, compared to a compression with parallel platens. Given the importance of platen misalignment angle an experimental setup and protocol are designed in order to maintain this angle below 0.1°, thus keeping the error on ET below 5%.

Nanomechanical subsurface characterisation of cellulosic fibres

AbstractThe mechanical properties of single fibres are highly important in the paper production process to produce and adjust properties for the favoured fields of application. The description of mechanical properties is usually characterised via linearized assumptions and is not resolved locally or spatially in three dimensions. In tensile tests or nanoindentation experiments on cellulosic fibres, only mechanical parameter for the whole fibre, such as elastic modulus or hardness, is usually obtained. To obtain a more detailed mechanical picture of the fibre, it is crucial to determine mechanical properties in depth. To this end, we discuss an atomic force microscopy-based approach to examine stepwise the local stiffness as a function of indentation depth via static force-distance curves. To our knowledge, we are the first authors to apply this method cellulosic fibres. The method was applied to linter fibres (extracted from a finished paper sheet) as well as to natural raw cotton fibres to better understand the influence of the pulp treatment process in paper production on the mechanical properties. Both types of fibres were characterised in dry and wet conditions with respect to alterations in their mechanical properties. The used stepwise analysis method of the force-distance curves allowed subsurface imaging of the fibres. It could be revealed how the walls in the fibre structure protects the fibre against mechanical loading. Via a combined 3D display of the mapped topography and the fitted elastic moduli in z-direction, a spatially resolved mechanical map of the fibre interior near the surface could be established. Additionally, we labelled the fibres with different carbohydrate binding modules tagged with fluorescent proteins to compare the AFM results with fluorescence confocal laser scanning microscopy imaging. Nanomechanical subsurface imaging in combination with fluorescent protein labelling is thus a tool to better understand the mechanical behaviour of cellulosic fibres, which have a complex, hierarchical structure.Graphical abstract

Dynamic Mechanical Properties of Several High-Performance Single Fibers.

High-performance fiber-reinforced composites (FRCs) are widely used in bulletproof structures, in which the mechanical properties of the single fibers play a crucial role in ballistic resistance. In this paper, the quasi-static and dynamic mechanical properties of three commonly used fibers, single aramid III, polyimide (PI), and poly-p-phenylenebenzobisoxazole (PBO) fibers are measured by a small-scale tensile testing machine and mini-split Hopkinson tension bar (mini-SHTB), respectively. The results show that the PBO fiber is superior to the other two fibers in terms of strength and elongation. Both the PBO and aramid III fibers exhibit an obvious strain-rate strengthening effect, while the tensile strength of the PI fiber increases initially, then decreases with the increase in strain rate. In addition, the PBO and aramid III fibers show ductile-to-brittle transition with increasing strain rate, and the PI fiber possesses plasticity in the employed strain rate range. Under a high strain rate, a noticeable radial splitting and fibrillation is observed for the PBO fiber, which can explain the strain-rate strengthening effect. Moreover, the large dispersion of the strength at the same strain rate is observed for all the single fibers, and it increases with increasing strain rate, which can be ascribed to the defects in the fibers. Considering the effect of strain rate, only the PBO fiber follows the Weibull distribution, suggesting that the hypothesis of Weibull distribution for single fibers needs to be revisited.

Nonlinear elastic response of pan based carbon fiber to tensile loading and relations to microstructure

In this study, wide- and small-angle scattering (WAXS, SAXS) are used to analyze the structure of polyacrylonitrile (PAN) carbon fiber. Wide angle scattering is used to identify lattice parameters such as d-spacings, stacking height of crystalline planes (Lc), average crystallize size (Lc), and various other features (void content, degree of graphitization). Small angle scattering results show orientation and size distributions of pores/amorphous regions. Several analysis techniques were applied to small angle scattering results to ensure accuracy. XRD Data collected is correlated to single fiber mechanical properties and a fiber model is developed. Fiber modulus is heavily related to crystallite dimensions and orientation as well as pore structure. Authors hypothesize that the non-linear elasticity observed in the fiber direction of carbon fibers arises from elastic planar motion within turbostratic carbon. As crystalline regions grow and expand, the lattice structure improves lowering the barriers for (002) quasi-graphene plane motion. This miniscule elastic planar motion can lead to a large nonlinear response to tensile loading especially for high crystallinity carbon fibers and underlying deformation mechanics is addressed considering transverse-isotropy of turbostatic graphite crystals.

Nonuniform loss of muscle strength and atrophy during bed rest: a systematic review.

Muscle atrophy and decline in muscle strength appear very rapidly with prolonged disuse or mechanical unloading after acute hospitalization or experimental bed rest. The current study analyzed data from short-, medium-, and long-term bed rest (5-120 days) in a pooled sample of 318 healthy adults and modeled the mathematical relationship between muscle strength decline and atrophy. The results show a logarithmic disuse-induced loss of strength and muscle atrophy of the weight-bearing knee extensor muscles. The greatest rate of muscle strength decline and atrophy occurred in the earliest stages of bed rest, plateauing later, and likely contributed to the rapid neuromuscular loss of function in the early period. In addition, during the first 2 wk of bed rest, muscle strength decline is much faster than muscle atrophy: on day 5, the ratio of muscle atrophy to strength decline as a function of bed rest duration is 4.2, falls to 2.4 on day 14, and stabilizes to a value of 1.9 after ∼35 days of bed rest. Positive regression revealed that ∼79% of the muscle strength loss may be explained by muscle atrophy, while the remaining is most likely due to alterations in single fiber mechanical properties, excitation-contraction coupling, fiber architecture, tendon stiffness, muscle denervation, neuromuscular junction damage, and supraspinal changes. Future studies should focus on neural factors as well as muscular factors independent of atrophy (single fiber excitability and mechanical properties, architectural factors) and on the role of extracellular matrix changes. Bed rest results in nonuniform loss of isometric muscle strength and atrophy over time, where the magnitude of change was greater for muscle strength than for atrophy. Future research should focus on the loss of muscle function and the underlying mechanisms, which will aid in the development of countermeasures to mitigate or prevent the decline in neuromuscular efficiency.NEW & NOTEWORTHY Our study contributes to the characterization of muscle loss and weakness processes reflected by a logarithmic decline in muscle strength induced by chronic bed rest. Acute short-term hospitalization (≤5 days) associated with periods of disuse/immobilization/prolonged time in the supine position in the hospital bed is sufficient to significantly decrease muscle mass and size and induce functional changes related to weakness in maximal muscle strength. By bringing together integrated evaluation of muscle structure and function, this work identifies that 79% of the loss in muscle strength can be explained by muscle atrophy, leaving 21% of the functional loss unexplained. The outcomes of this study should be considered in the development of daily countermeasures for preserving neuromuscular integrity as well as preconditioning interventions to be implemented before clinical bed rest or chronic gravitational unloading (e.g., spaceflights).

Humidity Controlled Mechanical Properties of Electrospun Polyvinylidene Fluoride (PVDF) Fibers

Processing parameters in electrospinning allow us to control the properties of fibers on a molecular level and are able to tailor them for specific applications. In this study, we investigate how relative humidity (RH) affects the mechanical properties of electrospun polyvinylidene fluoride (PVDF). The mechanical properties of single fibers were carried out using a specialized tensile stage. The results from tensile tests were additionally correlated with high-resolution imaging showing the behavior of individual fibers under tensile stress. The mechanical characteristic is strongly dependent on the crystallinity, chain orientation, and fiber diameter of electrospun PVDF fibers. Our results show the importance of controlling RH during electrospinning as the mechanical properties are significantly affected. At low RH = 30% PVDF fibers are 400% stiffer than their counterparts prepared at high RH = 60%. Moreover, the vast differences in the strain at failure were observed, namely 310% compared to 75% for 60% and 30% RH, respectively. Our results prove that humidity is a crucial parameter in electrospinning able to control the mechanical properties of polymer fibers.

Non-linear Scaling of Passive Mechanical Properties in Fibers, Bundles, Fascicles and Whole Rabbit Muscles.

Defining variations in skeletal muscle passive mechanical properties at different size scales ranging from single muscle fibers to whole muscles is required in order to understand passive muscle function. It is also of interest from a muscle structural point-of-view to identify the source(s) of passive tension that function at each scale. Thus, we measured passive mechanical properties of single fibers, fiber bundles, fascicles, and whole muscles in three architecturally diverse muscles from New Zealand White rabbits (n = 6) subjected to linear deformation. Passive modulus was quantified at sarcomere lengths across the muscle’s anatomical range. Titin molecular mass and collagen content were also quantified at each size scale, and whole muscle architectural properties were measured. Passive modulus increased non-linearly from fiber to whole muscle for all three muscles emphasizing extracellular sources of passive tension (p < 0.001), and was different among muscles (p < 0.001), with significant muscle by size-scale interaction, indicating quantitatively different scaling for each muscle (p < 0.001). These findings provide insight into the structural basis of passive tension and suggest that the extracellular matrix (ECM) is the dominant contributor to whole muscle and fascicle passive tension. They also demonstrate that caution should be used when inferring whole muscle properties from reduced muscle size preparations such as muscle biopsies.

Predicting the macroscopic response of electrospun membranes based on microstructure and single fibre properties

In the present paper, the three-dimensional structure and macroscopic mechanical response of electrospun poly(L-lactide) membranes is predicted based only on the geometry and elasto-plastic mechanical properties of single fibres supplemented by measurements of membrane weight and volume, and the resulting computational models are used to study the non-affine micro-kinematics of electrospun networks. To this end, statistical parameters describing the in-plane fibre morphology are extracted from scanning electron micrographs of the membranes, and computational network models are generated by matching the porosity of the real mats. The virtual networks are compared against computed tomography scans in terms of structure, and against uniaxial tension tests with respect to their macroscopic mechanical response. The obtained virtual network structure agrees well with the fibre disposition in real networks, and the rigorous prediction of the mechanical response of two membranes with mean diameters of 1.10μm and 0.70μm captures the experimental behaviour qualitatively. Favourable quantitative agreement, however, is obtained only after lowering the Young's moduli, yield stresses and hardening slopes determined in single fibre tests, and after reducing the density of inter-fibre bonds in the model of the membrane with thinner fibres. The simulations thus demonstrate the validity and merits of the approach to study the multi-scale mechanics of electrospun networks, but also point to potential discrepancies between the properties of electrospun fibres within a network and those produced for single fibre characterisation, and highlight the existing uncertainty on the density and quality of bonds between fibres in electrospun networks.

Transverse compressive properties of natural fibers determined using micro mechatronic systems and 2D full-field measurements

The literature focusing on the transverse mechanical properties of single fibers is very sparse compared to those related to longitudinal properties. An original characterization method is proposed herein, relying on a micro mechatronics device to implement a transverse compression test which is monitored using 2D full-field measurements. This is shown to allow for the identification of the transverse elastic properties of a single fiber. The method is used, at first, on a bio-based polymer monofilament (PA11) which is assumed to have regular and controlled dimensions and geometry. The transverse elastic modulus is identified to be equal to approximately 1500 MPa and the longitudinal modulus 2150 MPa. The proposed method is then used to investigate the transverse compressive behavior of contrasted natural fibers, such as beard hair (protein-based) and sisal fibers (polysaccharides-based) which have more complex shape and/or internal structure. This paper gives for the first time the compressive force displacement curves as well as the monitoring of the shape of the cross-section during the loading.

Digital Design and Automated Fabrication of Bespoke Collagen Microfiber Scaffolds.

A great variety of natural and synthetic polymer materials have been utilized in soft tissue engineering as extracellular matrix (ECM) materials. Natural polymers, such as collagen and fibrin hydrogels, have experienced especially broad adoption due to the high density of cell adhesion sites compared to their synthetic counterparts, ready availability, and ease of use. However, these and other hydrogels lack the structural and mechanical anisotropy that define the ECM in many tissues, such as skeletal and cardiac muscle, tendon, and cartilage. Herein, we present a facile, low-cost, and automated method of preparing collagen microfibers, organizing these fibers into precisely controlled mesh designs, and embedding these meshes in a bulk hydrogel, creating a composite biomaterial suitable for a wide variety of tissue engineering and regenerative medicine applications. With the assistance of custom software tools described herein, mesh patterns are designed by a digital graphical user interface and translated into protocols that are executed by a custom mesh collection and organization device. We demonstrate a high degree of precision and reproducibility in both fiber and mesh fabrication, evaluate single fiber mechanical properties, and provide evidence of collagen self-assembly in the microfibers under standard cell culture conditions. This work offers a powerful, flexible platform for the study of tissue engineering and cell material interactions, as well as the development of therapeutic biomaterials in the form of custom collagen microfiber patterns that will be accessible to all through the methods and techniques described here.Impact StatementCollagen microfiber meshes have immediate and broad applications in tissue engineering research and show high potential for later use in clinical therapeutics due to their compositional similarities to native extracellular matrix and tunable structural and mechanical characteristics. Physical and biological characterizations of these meshes demonstrate physiologically relevant mechanical properties, native-like collagen structure, and cytocompatibility. The methods presented herein not only describe a process through which custom collagen microfiber meshes can be fabricated but also provide the reader with detailed device plans and software tools to produce their own bespoke meshes through a precise, consistent, and automated process.

Study of solutions to optimize the extraction of hemp fibers for composite materials

Fibres from hemp stems can be extracted through different mechanical processes following dew or water retting etc. Extraction processes generally have a significant impact on mechanical and morphological properties of the fibres. In this study, hemp fibres are extracted following three different ways. In the first route hemp fibres are extracted from FUTURA 75 variety stems by performing scutching, hackling and microwave degumming. A second batch of fibres of the same variety was extracted by scutching and hackling after an initial microwave degumming treatment. In the third route, the same variety of hemp fibres are extracted from dew retted stems grown at Piacenza (Italy). Finally, the mechanical properties of single fibres as well as the fineness of technical fibres of all types of extracted fibres are evaluated and compared and the interest of the microwave degumming for hemp stem is evaluated.

Revealing non-crystalline polymer superstructures within electrospun fibers through solvent-induced phase rearrangements.

The design of nanofibers for biomedical applications requires a deep understanding of the fiber formation process and the resulting internal structure. In this regard, non-crystalline, mesomorphic structures play a central role in the processing of many polymers as precursors in the formation of crystalline superstructures (e.g. shish-kebab) and influence strongly the physical properties of polymers with a low degree of crystallinity. Yet, our ability to probe these relevant features is often greatly limited by their low contrast differences with the amorphous phase. We present an approach to reveal the organization of the mesomorphic superstructures within such polymeric materials, on the example of electrospun poly(l-lactide) nanofibers. Based on solvent-induced crystallization, this method employs fine-tuned solvent/non-solvent systems to enhance the contrast of these structural features by selectively triggering and controlling reorganization of the phases. Hereby, the mesomorphic regions are transformed into an α-crystalline phase, while the nanoscale spatial arrangement of the underlying superstructures is preserved. Combined with X-ray analytical techniques and electron microscopy, our approach provides detailed insights into the nanofiber's inner architecture, allowing for its direct visualization. Thereby, the influence of electrospinning parameters on the fiber formation process is explained as well as the impact of the resulting non-crystalline superstructures on single fiber mechanical properties. The method can be applied to comparable polymers for the development of materials with controlled, tailored properties.

Comparison of the mechanical characteristics of fibers and cell walls from moso bamboo and wood

Bamboo and wood fibers are important raw materials for pulp and papermaking, as well as fiber-reinforced composites. The mechanical properties of single fibers and the cell walls of moso bamboo (Phyllostachys heterocycla), Masson pine (Pinus massoniana), and Chinese fir (Cunninghamia lanceolata) were tested via single fiber tensile test and nanoindentation; their fracture characteristics were also compared. The single fibers and cell walls of moso bamboo had superior mechanical properties compared with those of Masson pine and Chinese fir. The bamboo fibers exhibited high strength, high elasticity, and superior ductility. The results indicated that the differences between the mechanical properties of the fiber cells and cell walls of moso bamboo and those of wood were largely dependent upon cell shape and structure.

Methyltrimethoxysilane plasma polymerization coating of carbon fiber surfaces

The adjustment of carbon fiber surface properties represents an important aspect to improve the adhesion behavior and the stress transfer between carbon fibers and polymeric matrices in carbon fiber reinforced polymers. In the presented work the surface of continuous carbon fiber tows composed out of 50,000 single fibers, so called 50k tows, is modified by an atmospheric plasma jet treatment of combined plasma activation and plasma polymerization, to improve adhesion to an epoxy matrix. Methyltrimethoxysilane is used as precursor gas to deposit a silicon organic layer. The developed experimental setup allows stable plasma treatment of more than 1200m of 50k carbon fibers, which were shown to be textile processable, and thus represents a promising route for surface treatment of carbon fibers for composite production. Largely homogeneous plasma deposition along and across the 50k carbon fiber tow is demonstrated by chemical surface analysis and high resolution microscopy. Single fiber mechanical properties are preserved under the plasma treatment.

Development of a method to measure mechanical properties of single elongated callose fibers in protoplast cultures of Larix leptolepis and Betula platyphylla

We developed a method to measure mechanical properties of single fibers of callose in liquid protoplast cultures of Larix leptolepis and Betula platyphylla, which were formed in media containing 50 mM of MgCl2 or 100 mM of CaCl2, respectively. Tensile test was performed using two micromanipulators loading micropipettes under an inverted microscope. Spring constant of the pipette used was first calibrated and calculated from using a microbalance. The callose fiber was wired between the two micropipettes. The Young’s modulus of single fibers for Larix and Betula was 7-9 kPa (1.4-1.9 x 104 N/m2) though the diameters of the fiber varied from 10 μm for Larix and 22-26 μm for Betula. No difference was found between experiments with and without medium containing high concentrations of salts. Tensile strength at break was 1.1-1.8 kPa (2.3-3.6 x 103 N/m2). The values are compared to other materials including cellulose containing plant cell wall, cell membranes, and amorphous callose. The value of the Young’s modulus observed was discussed.

Synthesis and characterization of lignin carbon fiber and composites

In this study, continuous lignin fibers from switchgrass have been successfully synthesized via multifilament melt-spinning and converted to carbon fibers using optimized stabilization and carbonization techniques. Unidirectional lignin carbon fiber reinforced composites are produced using a vacuum assisted resin transfer molding process for the first time. Produced lignin carbon fiber is evaluated in mechanical, interfacial, and microstructural areas. Single fiber mechanical properties are characterized using a unique MTS Bionix Nano-UTM. Interfacial properties and resin/fiber behavior are evaluated using single fiber fragmentation. Microstructural properties are determined using wide-angle x-ray diffraction. Mechanical results indicated an initial tensile modulus along fiber axis of 36 GPa and a failure stress of 600 MPa for single carbon fibers. Lignin carbon fibers demonstrate a nonlinear increase in modulus with applied tensile strain similar to recently observed for commercial poly-acrylonitrile (PAN) carbon fibers. Microscopy revealed few defects within and along the lignin carbon fibers, and the processed lignin fibers demonstrated minimal crystalline regions and crystallite alignment when compared to commercial PAN based fibers. Interfacial shear strength with epoxy resin was found to be 17 MPa with a fiber fracture length of 228 μm. Unidirectional composite coupons achieved tensile modulus of 9 GPa and a failure strength of 85 MPa at 1% failure strain. Lignin carbon fiber and composites produced are targeted for non-structural applications as mechanical properties are currently less than PAN carbon fibers and therefore are not suitable to replace PAN carbon fiber at this stage. Relatively low composite strength is the likely result of fiber layup, fiber fusing, and non-continuous fibers across the gage length of the composite. Nano-tensile and interface shear strength results presented here have important implications for lignin carbon fiber composite development to optimize fiber/resin bonding. In addition, composite manufacturing procedures detailed here are a major step forward in the development of sustainable carbon fiber composite production.

Influence of Thermal Annealing on the Mechanical Properties of PLLA Coiled Stents

To investigate the influence of elevated annealing temperature (70–90 °C) on the mechanical properties of coiled helical PLLA stents. PLLA 0.10 mm fibers and O3 mm × 12 mm stents were fabricated and annealed at 70, 80 and 90 °C for 25 min. The mechanical properties of the fibers and the functional characteristics of the stents were measured and compared to a control group processed at 21 °C. The stents were mounted, expanded and relaxed using an O3 mm × 2 cm balloon catheter to a maximum balloon pressure of 12 atm. Measurements of stent diameter, length, and the balloon pressure were used to determine the effective circumferential strain, incremental stiffness, elastic recoil, and lengthening of the stents. Stents exhibited progressively higher incremental stiffness with annealing temperature, higher collapse resistance and a reduction in elastic recoil vs. controls. Single fiber mechanical properties decreased as annealing temperature increased. Differential scanning calorimetry revealed crystallinity increased within thermally annealed stent fibers compared with controls. SEM examination indicated thermally annealed stents underwent less twisting than controls during balloon-induced unfurling. Thermal annealing of PLLA fibers and stents between 70 and 90 °C induced changes in crystalline structure, thereby favorably influencing fiber stress–strain behavior and stent expansion characteristics.

Properties of single electrospun poly (diol citrate)-collagen-proteoglycan nanofibers for arterial repair and in applications requiring viscoelasticity

Single nanofibers with chemical and functional properties consistent with artery extracellular matrix nanofibers were produced by electrospinning. Using weight ratios to mimic artery extracellular matrix, five materials were tested: (1) Collagen type I, (2) Collagen type I + Collagen type III, (3) Collagen type I + poly (diol citrate), (4) Collagen type I + Collagen type III + poly (diol citrate), and (5) Collagen type I + poly (diol citrate) + Decorin + Aggrecan. Fiber sizes for all materials ranged from 50 nm to 600 nm and random fiber mats had pore sizes from 21 to 40 = m(2) and porosities of 72-84%. Human embryonic palatal mesenchymal cells fibroblasts adhered to all fibers and proliferated over a 7-day study period. Mechanical properties of single fibers were investigated using a combined atomic force/optical microscope. Materials containing poly (diol citrate) showed elasticity increased 3.2 fold greater than composites without poly (diol citrate). Maximum stress was within functional range in comparison to decellularized artery extracellular matrix fibers. By incorporating poly (diol citrate) and proteoglycan along with collagen, a viscoelastic nanofibrous material was produced for use in tissues such as artery where viscoelasticity and tensile strength are required.

Effect of high temperature heat treatment on the microstructure and mechanical properties of third generation SiC fibers

ABSTRACTSiC fibers (High Nicalon S -HNS and Tyranno SA3 -Ty-SA3) submitted to heat treatments in neutral atmosphere up to 1900°C were studied by X-ray diffraction (XRD) and TEM observations then submitted to tensile tests up to 1800°C. The microstructural changes in both materials were determined by XRD using a modified Hall-Williamson method introducing an anisotropy parameter taking into account the high density of planar defects of the SiC-3C structure. HNS fibers exhibit significant modifications in the CDD size which drastically increases from 24 nm to 70 nm in the range 1600°C to 1800°C and in the microstrains which decrease from 0.0015 to 0.0005 between 1750°C to 1850°C. Concerning the Ty-SA3 fibers, no evolution of CDD size and microstrains has been observed. The mechanical properties of single fibers were investigated after the heat treatments showing decreases in the tensile strength reaching up to 20% for Tyranno SA3 and 50% for High Nicalon S. The Weibull moduli were also significantly affected. These results are correlated to the fiber structural and microstructural evolutions.