No description available.

Due to its unique characteristics, carbon fiber is one of the leading materials for light weight, high strength and stiffness applications in composite materials. The development of carbon fibers approaching theoretical strengths and stiffness is a continuing process which has led to improved mechanical and physical properties over the recent years. Improvements in carbon fiber properties are directly dependent on the quality of the precursor fiber. Research and development of PAN precursor fiber requires extensive experimentation to determine how processing conditions affect the structure and properties of the precursor fibers. Therefore, it is the goal of this thesis to analyze the results of varying coagulation rates on fiber shape, density and porosity, to determine the effect of cross-sectional shape, density, and fiber diameter on the tensile strength of the fiber, and to investigate the most effective method for the reduction of fiber diameter. Results indicate a low temperature, high solvent concentration coagulating bath leads to a rounder cross section with lower void content. Reduction in fiber diameter was found to increase tensile strength while increased molecular orientation experienced during high draw down ratios led to an increase in fiber modulus.

Diverse fiber-forming proteins are found in nature that accomplish a wide range of functions including signaling, cell adhesion, and mechanical support. Unique sequence characteristics of these proteins often lead to their specialized roles. However, these proteins also share a common organizational hierarchy in primary and secondary structures that strongly influence both their intramolecular folding and intermolecular interactions. Based on what is known regarding protein fiber assembly of silk peptides, shear-induced elongation of the molecular strands drives interchain secondary structure crystallization via anisotropic alignment, which creates a molecular superstructure that forms the basis a fiber network. In this work, the hypothesis is this type of protein fiber assembly is not unique to silk sequences and that other proteins can be spun into fibers in similar fashion while maintaining unique functionality given by their specialized amino acid sequences such as RGD, GX1X2, and so forth. This was investigated by modeling the manner in which hydrophobic and hydrophilic blocks of amino acids create interacting secondary structures at the chain level when exposed to shear. It was determined computationally and then verified experimentally that fiber spinning success is most likely to occur after shear processing if the protein sequence exhibits a balance of hydrophobic and hydrophilic content and has sufficient length. Applied to the biological scale, both pure and mixed solutions of proteins such as fibronectin, laminin, and silk fibroin were spun into fibers. In particular, alloy protein fibers of silk fibroin mixed with fibronectin exhibited the characteristic mechanical integrity of silk and the bioactivity of fibronectin. This simple method of creating protein fibers with hybrid characteristics is significantly faster, less expensive, and less technically intensive than chimeric protein production, which purports to do the same. This finding also provides insight into a fundamental means by which protein fibers may be assembled in vivo by taking advantage of the thermodynamically favorable assembly of peptide sequences at the chain level under proper molecular orientation. Taken together, a high throughput means of producing a wide-range of pure and hybrid protein fibers has been developed for various biological applications and research investigations into the fibrous elements of biology.

Tissue engineering is a multidisciplinary field that is rapidly emerging as a promising new approach in the restoration and reconstruction of tissues. In this approach, three dimensional (3D) scaffolds are of great importance. Scaffolds function both as supports for cell growth and depot for sustained release of required active agents (e.g. enzymes, genes, antibiotics, growth factors). Scaffolds should possess certain properties in accordance with usage conditions. Wet-spinning is a simple technique that has been widely used for the fabrication of porous scaffolds for tissue engineering applications. Natural polymers can effectively be used in scaffold fabrication due to their biocharacteristics. Among natural polymers, chitosan and alginate are two of the most studied ones in tissue engineering and drug delivery fields because of being biologically renewable, biodegradable, biocompatible, non-antigenic, non-toxic and biofunctional. In this study, two kinds of porous scaffolds were produced as chitosan and alginate coated chitosan fibrous scaffolds by wet-spinning technique In order to investigate the delivery characteristics of the scaffolds, loading of gentamicin as a model antibiotic and bovine serum albumin (BSA) as a model protein was carried out in different loading models. Resultant scaffolds were characterized in terms of their structural formation, biodegradation, biomineralization, water uptake and retention ability and mechanical properties. Additionally, release kinetics of gentamicin and BSA were examined. Efficiency of gentamicin on Escherichia coli (E.coli) was examined. Characterization of scaffolds revealed their adequacy to be used in bone tissue engineering applications and capability to be employed as bioactive agent delivery systems.

In this study a microbial polyester, poly(3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV), and its blends were wet or electrospun into fibrous scaffolds for tissue engineering. Wet spun fiber diameters were in the low micrometer range (10-50 &amp / #956 / m). The polymer concentration and the stirring rate affected the properties the most. The optimum concentration was determined as 15% (w/v). Electrospun fiber diameters, however, were thinner. Solution viscosity, potential, distance between the syringe tip and the collector, and polymer type affected the morphology and the thickness of beads formed on the fibers. Concentration was highly influential / as it increased from 5% to 15% (w/v) fiber diameter increased from 284 &plusmn / 133 nm to 2200 &plusmn / 716 nm. Increase in potential (from 20 to 50 kV) did not lead to the expected decrease in fiber diameter. The blends of PHBV8 with lactide-based v polymers (PLLA, P(L,DL-LA) and PLGA (50:50)) led to fibers with less beads and more uniform thickness. In vitro studies using human osteosarcoma cells (SaOs-2) revealed that wet spun fibers were unsuitable because the cells did not spread on them while all the electrospun scaffolds promoted cell growth and penetration. The surface porosities for PHBV10, PHBV15, PHBV-PLLA, PHBV-PLGA (50:50) and PHBV-P(L,DL)LA were 38.0&plusmn / 3.8, 40.1&plusmn / 8.5, 53.8&plusmn / 4.2, 50.0&plusmn / 4.2 and 30.8&plusmn / 2.7%, respectively. Surface modification with oxygen plasma treatment slightly improved the cell proliferation rates. Consequently, all scaffolds prepared by electrospinning revealed a significant potential for use in bone tissue engineering applications / PHBV-PLLA blend appeared to yield the best results.

No description available.

The aim of this project was to address the food waste problem, particularly bread waste, to some extent by producing monofilaments obtained from wet spinning of fungal hydrogel through the cultivation of Rhizopus delemar on bread waste. The project had two phases. Firstly, the possibility of production of chitosan fiber with wet spinning (using different acids) was evaluated, the process was optimized, and then applied to the production of fungal fiber. Regarding first stage of the project, adipic acid, a non-toxic solvent with two carboxyl groups, was used as acting physical crosslinker between the chitosan chains, resulting in improving properties of the monofilaments. Adipic acid performance was compared with conventional solvents, such as citric, lactic, and acetic acids. By injecting chitosan solutions into a coagulation bath (EtOH or NaOH 1M or EtOH-NaOH or H2SO4-EtOH), monofilaments were formed. Scanning electron microscopy showed that uniform chitosan monofilaments with smooth surface were formed using adipic and lactic acids. In general, fibers obtained from adipic acid displayed higher mechanical strength (Young’s modulus of 4.45 GPa and tensile strength of 147.9 MPa) than that of monofilaments produced using conventional solvents. Fiber dewatering with EtOH before drying led to greater fiber diameter and lower mechanical strength. As the second stage of this study, Rhizopus delemar was cultivated on bread waste in shake flasks and 1.3 M3 bioreactor. While different combinations of ground bread and K2HPO4 was used as the substrate for shake flask cultivations, white bread waste without K2HPO4 was utilized for scaling up the process, mostly due to the Glucosamine (GlcN) and N-acetyl-glucosamine (GlcNAc) content in the fungal cell wall. GlcN and GlcNA content obtained from ground bread was remarkably higher than that of obtained from combinations of ground bread and K2HPO4 as the substrate. Cultivation in 1.3 M3 bioreactor resulted in about 36 kg wet biomass with a mean of 14.88% dry weight, indicating 5.95 g biomass/L. The biomass yield of 0.15 g dry biomass/g dry bread was achieved. Alkali insoluble material (AIM) was obtained by alkali treatment of biomass. Fungal hydrogel was prepared by adding adipic and lactic acid to AIM, followed by grinding treatment. While hydrogels treated with lactic acid showed better spinnability and gelling ability, the one from adipic acid was not uniform to be wet spun. Considering hydrogels treated with lactic acid, the optimum grinding cycle for more spinnable hydrogel was 6 negative cycles, contributing to the fibers with the tensile strength of around 82 MPa. Such fibers showed antibacterial property against Escherichia coli, making them as a good option for suture applications. However, further in vitro and in vivo trials are essential to test the fungal fiber for such applications.

Dans ces travaux de recherche, la préparation de fibres d'alginate de calcium revêtues de chitosane par un procédé de filage par mouillage et la caractérisation de ces fibres dont leur activité antibactérienne sont présentées. Un métier à filer à l'échelle pilote a été conçu et développé au cours de ces travaux de thèse pour l'élaboration de fibres d'alginate de calcium. Ces dernières, préalablement fabriquées, sont immergées dans une solution d'acétate de chitosane. Trois méthodes de coagulation de l'enduit de chitosane ont été explorés dont deux consistent en l'immersion des fibres dans un bain neutralisant : une solution de dihydroxyde de calcium ou une solution d'hydroxyde de potassium. La dernière méthode consistait à neutraliser le chitosane par séchage sous air chaud soufflé. Une caractérisation structurelle, mécanique et d'absorption des fibres, ainsi qu'un dosage du chitosane revêtu ont été réalisés. De plus, une évaluation antibactérienne a été accomplie par une méthode de comptage des UFC (Unité Formant Colonie) après 6 h d'incubation à 37 °C. L'incorporation de chitosane aux fibres d'alginate de calcium apporte une activité antibactérienne contre Staphylococcus epidermidis, Escherichia coli et divers Staphylococcus aureus tels que MSSA (Methicillin Sensitive Staphylococcus aureus), CA-MRSA (Community Associated Methicillin Resistant Staphylococcus aureus) et HA-MRSA (Healthcare Associated Methicillin Resistant Staphylococcus aureus). Ces fibres revêtues sont alors des candidats de choix pour l'élaboration de tissus destinés à la cicatrisation des plaies. Développer des compresses avec les propriétés hémostatiques et cicatrisantes de l'alginate de calcium combinées aux propriétés antibactériennes du chitosane peut être envisagé pour lutter contre les infections et plus particulièrement les maladies nosocomiales / In this work, the preparation of chitosan-coated alginate fibers by a wet spin process and the characterization of these fibers, particularly their antibacterial activities are presented. A pilot scale spinning machine was developed during this thesis for the elaboration of calcium alginate fibers. These last, preformed produced were immersed in chitosan acetate solutions. Three coagulation methods of the chitosan coating were explored two of which consist to the immersion of the fibers in a neutralizing bath: a calcium hydroxide solution or a potassium hydroxide solution. The last method is to neutralize chitosan by drying under hot air blown. Structural, mechanical and absorption characterization of fibers and a dose of the coated chitosan have been made. Furthermore, the antibacterial evaluation was achieved by a CFU (Colony-Forming Units) counting method after 6 h of incubation at 37 °C. The incorporation of chitosan on calcium alginate fibers brings antibacterial activities against Staphylococcus epidermidis, Escherichia coli and various Staphylococcus aureus strains namely MSSA (Methicillin Sensitive Staphylococcus aureus), CA-MRSA (Community Associated Methicillin Resistant Staphylococcus aureus) and HA-MRSA (Healthcare Associated Methicillin Resistant Staphylococcus aureus) which make these chitosan-coated fibers potential candidates for wound dressing materials. Developing a wound dressing with the haemostatic and healing properties of alginate combined with antibacterial properties of chitosan can be envisioned for fighting against the infections and more particularly nosocomial infections

Le chitosane est un polymère naturel obtenu par deacétylation de la chitine. Ce polysaccharide est bien connu pour ses propriétés biologiques exceptionnelles : il est biocompatible et biorésorbable. Les fibres de chitosane peuvent être utilisées en chirurgie. L'objectif de cette thèse est d'étudier les phénomènes physico-chimiques mis en jeu, de développer un modèle du procédé, afin d'optimiser le procédé de filage mis au point au laboratoire.Après une revue de la littérature dans le premier chapitre, les techniques expérimentales d'obtention, de purification, et de caractérisation du chitosane sont décrits dans le deuxième chapitre. Une étude de la structure du chitosane obtenu est présentée. C'est l'un des résultats originaux de ce travail.Le principe du procédé étant par coagulation en solution, il est essentiel de déterminer dans quelle condition celle-ci s'effectue, et quel est le paramètre déterminant. Les études précédentes ont montré que celui-ci est le coefficient de diffusion de la soude dans le milieu. A cet effet, des mesures ont été effectuées, dans des géométries différentes. Cette étude constitue le travail présenté dans le chapitre trois.Dans le chapitre quatre est présentée une technique consistant à suivre au moyen d'un microscope l'avancée du front de coagulation. Cette technique a permis de déterminer précisément le coefficient de diffusion.Le dernier chapitre a consisté à élaborer des fibres au moyen d'un banc que possède le laboratoire (IMP Lyon 1). L'étape ultime de ce travail a été de modéliser le procédé, de prévoir les diamètres intérieur et extérieur des fibres obtenues, et de comparer le résultat de la modélisation aux résultats expérimentaux / Chitosan is a natural polymer obtained by deacetylation of chitin. This polysaccharide is well known for its exceptional biological properties: it is biocompatible and bio absorbable. Chitosan fibers can be used in surgery.The objective of this thesis is to study the physicochemical phenomena involved, to develop a process model, to optimize the filtering process in the laboratory.After a review of the literature in the first chapter, the experimental techniques for obtaining, purifying and characterizing chitosan are described in the second chapter. A study of the structure of the chitosan obtained is presented. This is one of the original results of this work.The principle of the coagulation method in solution, it is essential to determine in what condition it, and what is the determining parameter. Previous studies have shown that this is the diffusion coefficient of soda in the medium. One effect, measurements were made, in different geometries. This study constitutes the work presented in Chapter Three.In chapter four is presented a technique consisting in following by means of a microscope the advance of the coagulation front. This technique makes it possible to determine the diffusion coefficient.The last chapter consisted of developing fibers using a small scale plant existing in laboratory (IMP Lyon 1). The final element of this work consists of modelling the process, calculating the inside and outside diameters of the fibers obtained and comparing the result of the modelling with the experimental results

abstract: Polymer fibers have broad applications in wearable electronics, bulletproof vests, batteries, fuel cells, filters, electrodes, conductive wires, and biomedical materials. Polymer fibers display light density and flexibility but are mostly weak and compliant. The ceramic, metallic, and carbon nanoparticles have been frequently included in polymers for fabricating continuous, durable, and functional composite fibers. Nanoparticles display large specific areas, low defect density and can transfer their superior properties to polymer matrices. The main focus of this thesis is to design, fabricate and characterize the polymer/nanocarbon composite fibers with unique microstructures and improved mechanical/thermal performance. The dispersions and morphologies of graphene nanoplatelets (GNPs), the interactions with polyvinyl alcohol (PVA) molecules and their influences on fiber properties are studied. The fibers were fabricated using a dry-jet wet spinning method with engineered spinneret design. Three different structured fibers were fabricated, namely, one-phase polymer fiber (1-phase), two-phase core-shell composite fiber (2-phase), and three-phase co-axial composite fiber (3-phase). These polymer or composite fibers were processed at three stages with drawing temperatures of 100˚C, 150˚C, and 200˚C. Different techniques including the mechanical tester, wide-angle X-Ray diffraction (WAXD), scanning electron microscope (SEM), thermogravimetric analysis (TGA), and differential scanning calorimeter (DSC) have been used to characterize the fiber microstructures and properties. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2018