Electrospinning is a process by which micro and nanofibrous scaffolds can be easily fabricated to mimic structures such as the extracellular matrix of bone. A number of materials have been used to fabricate such scaffolds making the process an extremely versatile tool in the field of bone tissue engineering. Many scaffolds however are hydrophobic, leading to poor cellular attachment and proliferation, whilst the actual process of electrospinning is highly variable, producing irregular scaffolds that can ultimately influence cell invasion and differentiation. The focus of this thesis was to address the issues of poor biocompatibility and irregular scaffold production in three commonly used polymers each with different mechanical properties and degradation profiles. Poly (ε-caprolactone) (PCL), polyethylene terephthalate (PET) and poly lactic-co-glycolic acid (PLGA) were functionalised with surfactants in order to improve the biocompatibility and osteoinductive properties of electrospun scaffolds, whilst electrospinning equipment was modified to improve uniformity of scaffold production. Reducing variables known to affect scaffold formation such as temperature and humidity through the use of an environmental stability cabinet improved the reproducibility of scaffolds. The introduction of a Faraday cage, a larger electrode and a negative mandrel potential also improved the quality and quantity of electrospun fibres collected. Lecithin was selected as an appropriate additive for both improving biocompatibility and uniformity of electrospun fibres as it is naturally occurring and induced dose dependent reductions in water contact angle, allowing tailored hydrophobicity. Through gravimetric determination of pore sizes coupled with mathematical modelling, the addition of lecithin was found to reduce both mean fibre diameter and pore size in all scaffolds, improving scaffold homogeneity. At low concentrations (i.e. 2 %) lecithin generally did not affect the mechanical properties of scaffolds, however significant improvements in tensile strength for PCL and nanoindentation for PET were evident, indicating these scaffolds remained suitably strong for bone regeneration purposes. Reduced hydrophobicity acted to improve cellular attachment of Saos-2 osteoblasts to polymers, whilst proliferation on all scaffolds was similar to TCP controls. Furthermore, lecithin incorporation induced osteoinduction, as bone marrow mesenchymal stem cells seeded on these hybrid scaffolds expressed upregulated gene expression for alkaline phosphatase, collagen 1, osteocalcin and osteopontin. In conclusion, these scaffolds, functionalised with lecithin, improve the homogeneity of fibrous mats allowing increased reproducibility and efficiency of the electrospinning process. Furthermore, the improved biocompatibility and osteoinductivity that lecithin presents, allows for the production of more suitable electrospun scaffolds in the field of bone tissue engineering.

In Tissue Engineering, scaffolds composed of natural polymers often show a distinct lack in stability. The natural polymer gelatin is highly fragile under physiological conditions, nevertheless displaying a broad variety of favorable properties. The aim of this study was to fabricate electrospun gelatin nanofibers, in situ functionalized and stabilized during the spinning process with highly reactive star polymer NCO-sP(EO-stat-PO) (“sPEG”). A spinning protocol for homogenous, non-beaded, 500 to 1000 nm thick nanofibers from different ratios of gelatin and sPEG was successfully established. Fibers were subsequently characterized and tested with SEM imaging, tensile tests, water incubation, FTIR, EDX, and cell culture. It was shown that adding sPEG during the spinning process leads to an increase in visible fiber crosslinking, mechanical stability, and stability in water. The nanofibers were further shown to be biocompatible in cell culture with RAW 264.7 macrophages. / Tissue Engineering Scaffolds aus natürlichen Polymeren zeigen häufig mangelnde Stabilität, insbesondere unter physiologischen Bedingungen. Das natürliche Polymer Gelatine besitzt einige sehr vorteilhafte Eigenschaften für die Anwendung bei der Produktion künstlicher Körpergewebe. Beim Einsatz im menschlichen Organismus ist die Gelatine durch ihre Wasserlöslichkeit höchst fragil. Das Ziel dieser Arbeit war die Herstellung von Nanofaser-Scaffolds aus Gelatine mittels Elektrospinning und deren in situ Stabilisierung durch das Sternpolymer NCO-sP(EO-stat-PO) („sPEG“). Zunächst wurde ein Spinningprotokoll zur Fabrikation homogener, glatter, 500 bis 1000 nm dicker Nanofasern in verschiedenen Verhältnissen von Gelatine und sPEG erarbeitet. Mittels REM Bildgebung, Zugversuchen, Wasserinkubationsversuchen, FTIR, EDX und Zellkultur wurden die Fasern untersucht und charakterisiert. Es konnte gezeigt werden, dass die Zugabe von sPEG während des Spinningprozesses zu einer sichtbaren Quervernetzung der Fasern, sowie zu einem Anstieg der mechanischen Festigkeit und der Wasserstabilität führt. Des Weiteren wurde die Biokompatibilität der Nanofasern in der Zellkultur mit RAW 264.7 Makrophagen belegt.

Bänder und Sehnen sind bradytrophe Gewebe die eine limitierte intrinsische Heilungskapazität aufweisen. Trotz einer primären Nahtrekonstruktion kann es zur Ausbildung eines mechanisch insuffizienten Narbengewebes kommen. Die Verwendung autologer oder allogener Sehnen-/Bandersatzplastiken bei Vorliegen substantieller Defekte bergen die Gefahr der donor site morbidity und antigener/allergischer Reaktionen. Besonders das Tissue Engineering kann hier zur Entwicklung innovativer Therapieansätze beitragen. Die Verwendung autologer mesenchymaler Vorläuferzellen und biomimetischer Zellträger zu Generierung eines Sehnen- /Bandersatzes ex vivo ist eine vielversprechende Alternative. Ziel der vorliegenden Arbeit war die Generierung von biomimetischen Zellträgern auf der Basis von Kollagen Typ I mittels Elektrospinning. Dabei orientierte sich das Scaffolddesign am Aufbau der EZM von nativem Band- und Sehnengewebe. In einem zweiten Schritt wurde die Auswirkung unterschiedlicher Scaffoldarchitektur auf die tenogene Differenzierung von humanen MSZ untersucht. Hierzu wurden MSZ aus dem Knochenmark isoliert, amplifiziert, die Zellträger mit diesen Zellen besiedelt und für einen definierten Zeiträum (21 Tage) kultiviert. Die Kollagen I-Ausgangskonzentration hatte entscheidenden Einfluss auf den Faserdurchmesser. Wobei unter Verwendung einer 5-8%-igen Kollagenlösung der Faserdurchmesser im Bereich von nativen Kollagenfasern in natürlichem Sehnengewebe erzielt werden konnte. Unter Verwendung eines rotierenden Metallzylinders als Kollektor konnte mit steigender Rotationgeschwindigkeit eine zunehmende parallele Faserausrichtung in den NFS erreicht werden. Ein Einfluss auf die Morphologie und die Proliferation der MSZ auf NFS mit unterschiedlicher Faserdicke zeigte sich nicht. Ausgerichtete Fasern führten zu einer signifikant parallelen Ausrichtung der MSZ mit langgezogenem schlanken Zellkörper, im Unterschied zu einer polygonalen MSZ-Morphologie auf nicht ausgerichteten NF. Die tenogene Differenzierung der Zellen in den NFS wurde mittels RT-PCR- Analyse untersucht. Hierbei wurde die Expression der tendogenen Markergene Tenascin C, Elastin, Kollagen I und Skleraxis bestimmt. Zusätzlich wurden immunfluoreszens- und histochemische Färbungen durchgeführt, um die Infiltration der Zellen in die Zellträger und den Einfluss unterschiedlicher Faserparameter auf die Morphologie der MSZ nachzuweisen. Unter Verwendung von ausgerichteten Kollagen I-NFS zeigte sich eine signifikant höhere tenogene Markergenexpression für Skleraxis und Tenascin C in der Frühphase und im weiteren Verlauf ebenfalls für Col I und Elastin im Vergleich zu nicht ausgerichteten NFS. Elektrospinning von Kollagen I unter Verwendung eines rotierenden Kollektors ermöglicht die Herstellung biomimetischer NFS mit paralleler Faserausrichtung analog zu nativem Sehnengewebe. Die so hergestellten NFS zeichnen sich im Vergleich zu nicht ausgerichteten NFS durch eine signifikant höher mechanische Zugfestigkeit und die Induktion einer tenogenen Markergenexpression in MSZ aus. Prinzipiell haben Kollagen I-NFS das Potential bestehende Therapiestrategien zu Rekonstruktion substantieller Sehnenrupturen im Rahmen Stammzell-basierter Ansätze zu unterstützen. Die generelle Eignung in vivo muss aber zunächst in adäquaten Großtiermodellen (z. B. Rotatorenmanschettendefekt im Schaf) überprüft werden. Die vorliegende Arbeit zeigt die Bedeutung eines Zielgewebe-gerichteten Designs von Zellträgern für die Entwicklung innovativer Strategien im Tissue Engineering. Bei der Regeneration muskuloskelettaler Gewebe, wie dem Sehnenegewebe, spielen nicht nur strukturelle Aspekte sondern auch die biochemische Zusammensetzung des zu erneuernden Gewebes eine entscheidende Rolle, die bei der Scaffold-Herstellung zu berücksichtigen sind. / In vitro studies of tenogenous differentiation of human mesenchymal stem cells in collagen -I-nanofaserscaffolds for the replacement of tendons

<p>The time when it will be possible to grow complex organs in a lab environment comes closerdue to the rapid progress taking place in the area of biotechnology and tissue engineering.Various tissue engineering methods of creating artificial scaffolds has evolved, one of thosebeing electrospinning. Electrospun scaffolds are beneficial in tissue engineering applicationsforemost in regard to their body-mimicking structure. Small pore sizes and low porosities mayhowever limit cell infiltration and thereby creation of 3D functional tissues. The issue of cellinfiltration in electrospun constructs such as nonwoven polymer scaffolds for use in tissueengineering may be solved by a method of simultaneous integration i.e. integrating particlesduring the phase of production in the electrospinning process. In this thesis investigation of aproof-of-concept to the idea of in the future distributing living cells within the threedimensionalstructure during the process of electrospinning of a polymeric biomaterial weremade. To be able to conduct simple experiments glass particles with proper sizes are used tosubstitute living cells. During this thesis a novel method called spray electrospinning tookshape enabling a fine distribution of particles in an electrospun material.The work in this thesis shows that there are methods to simultaneously integrate particles inproduction of scaffold materials, one of these composed of spraying particles whileelectrospinning on a rotating collector. The experiments were done in order to compare thedifferent methods; Double, Coaxial and Spray electrospinning pointing out similarities anddifferences between the three. The methods used to characterize the materials include scalemeasurements and SEM image analysis to determine morphology, fibre diameter, layerthickness and distance between particles. Glass particles were used as substitutes for livingcells for the sake of proof of concept which showed that these can successfully be integratedsimultaneously in an electrospun material. However porosity and the number of particles haveto be further optimized for the material to be ready for use in tissue engineering.The time when it will be possible to grow complex organs in a lab environment comes closerdue to the rapid progress taking place in the area of biotechnology and tissue engineering.Various tissue engineering methods of creating artificial scaffolds has evolved, one of thosebeing electrospinning. Electrospun scaffolds are beneficial in tissue engineering applicationsforemost in regard to their body-mimicking structure. Small pore sizes and low porosities mayhowever limit cell infiltration and thereby creation of 3D functional tissues. The issue of cellinfiltration in electrospun constructs such as nonwoven polymer scaffolds for use in tissueengineering may be solved by a method of simultaneous integration i.e. integrating particlesduring the phase of production in the electrospinning process. In this thesis investigation of aproof-of-concept to the idea of in the future distributing living cells within the threedimensionalstructure during the process of electrospinning of a polymeric biomaterial weremade. To be able to conduct simple experiments glass particles with proper sizes are used tosubstitute living cells. During this thesis a novel method called spray electrospinning tookshape enabling a fine distribution of particles in an electrospun material.The work in this thesis shows that there are methods to simultaneously integrate particles inproduction of scaffold materials, one of these composed of spraying particles whileelectrospinning on a rotating collector. The experiments were done in order to compare thedifferent methods; Double, Coaxial and Spray electrospinning pointing out similarities anddifferences between the three. The methods used to characterize the materials include scalemeasurements and SEM image analysis to determine morphology, fibre diameter, layerthickness and distance between particles. Glass particles were used as substitutes for livingcells for the sake of proof of concept which showed that these can successfully be integratedsimultaneously in an electrospun material. However porosity and the number of particles haveto be further optimized for the material to be ready for use in tissue engineering.</p>

The current thrust towards the compaction of electrical power equipment, resulting in increased insulation electrical stress levels, necessitates new electrical insulating materials. In the last few decades, polymeric materials that exhibit light weight, excellent mechanical properties, low cost, and some with unique non-wetting surface characteristics, have surpassed the use of the conventional porcelain and glass insulating materials. Despite these advantages, polymeric materials are incapable of withstanding the high heat from surface arcing that is instigated by the synergism of pollution, moisture, and voltage. Surface arcing results in material loss due to heat ablation and/or the electrical tracking of polymeric materials. To overcome such issues, inorganic fillers are added to the base polymers to enhance their resistance to surface discharge activities and other performances. Since their addition can significantly reduce material costs, their use is compelling. Micron-sized fillers, here after defined as microfillers, have been used to acquire these desirable properties, but due to limitations in material processability, the further application of such fillers is limited. Consequently, nano-sized fillers, here after defined as nanofillers, have been viewed as replacements or assistant combinations to microfillers. Nanofillers are characterized by large surface areas, resulting in increased bond strengths that yield significant improvements in the various properties at fill levels well below that of microfillers. However, the primary problem of using nanofillers is their characteristic property of agglomeration due to their physical size and the forces between the fillers. Conventional mechanical mixing of nanofillers does not adequately separate the nanofillers, leading to behaviour similarly to that of microfillers. Therefore, the implementation of nanofillers is not completely effective. In chemical dispersion techniques, for example, the use of surfactants, are normally very elaborate and complicated. Due to the negative impact of agglomeration, the successful dispersion of nanofillers is pivotal in the further development of nanodielectrics for various insulation applications. In this thesis, electrospinning is proposed and realized as a new dispersal method for nanofillers in polymeric materials. This novel technique facilitates polymeric nanocomposites with improved properties due to the uniform distribution of fillers. Scanning electron microscopy (SEM) images and energy dispersive X-ray analysis (EDX) clearly indicate that electrospun nanocomposites demonstrate a better filler distribution than nanocomposites, produced by conventional mechanical mixing. Also electrospinning introduces the possibility of separating different nanofillers in different base polymers. The mechanical properties: tensile strength and hardness; the electrical properties: permittivity, tracking, and erosion resistance; and the thermal properties: thermal conductivity, thermal degradation, and heat erosion resistance of electrospun nanocomposites are compared to those of conventional nanocomposites for silicone rubber and cycloaliphatic epoxy-based polymers. All the experimental studies in this thesis confirm that electrospun nanocomposites exhibit better thermal performances than the conventional composites which are attributed to the improved distribution of the nanofillers by the newly developed electrospinning process. Also in this investigation, a two-dimensional thermal model is developed in COMSOL MultiphysicsTM by using the finite element method (FEM) to theoretically address the benefits of using nanofillers and the effects of filler dispersion. The model confirms that electrospun nanocomposites have much more uniform temperature distribution than conventional nanocomposites. This thesis presents the possible mechanisms by which nanofillers improve the heat and erosion resistance of silicone rubber nanocomposites, and also addresses the possible mechanism by which electrospinning improves nanofiller dispersion.

No description available.

The time when it will be possible to grow complex organs in a lab environment comes closerdue to the rapid progress taking place in the area of biotechnology and tissue engineering.Various tissue engineering methods of creating artificial scaffolds has evolved, one of thosebeing electrospinning. Electrospun scaffolds are beneficial in tissue engineering applicationsforemost in regard to their body-mimicking structure. Small pore sizes and low porosities mayhowever limit cell infiltration and thereby creation of 3D functional tissues. The issue of cellinfiltration in electrospun constructs such as nonwoven polymer scaffolds for use in tissueengineering may be solved by a method of simultaneous integration i.e. integrating particlesduring the phase of production in the electrospinning process. In this thesis investigation of aproof-of-concept to the idea of in the future distributing living cells within the threedimensionalstructure during the process of electrospinning of a polymeric biomaterial weremade. To be able to conduct simple experiments glass particles with proper sizes are used tosubstitute living cells. During this thesis a novel method called spray electrospinning tookshape enabling a fine distribution of particles in an electrospun material.The work in this thesis shows that there are methods to simultaneously integrate particles inproduction of scaffold materials, one of these composed of spraying particles whileelectrospinning on a rotating collector. The experiments were done in order to compare thedifferent methods; Double, Coaxial and Spray electrospinning pointing out similarities anddifferences between the three. The methods used to characterize the materials include scalemeasurements and SEM image analysis to determine morphology, fibre diameter, layerthickness and distance between particles. Glass particles were used as substitutes for livingcells for the sake of proof of concept which showed that these can successfully be integratedsimultaneously in an electrospun material. However porosity and the number of particles haveto be further optimized for the material to be ready for use in tissue engineering.The time when it will be possible to grow complex organs in a lab environment comes closerdue to the rapid progress taking place in the area of biotechnology and tissue engineering.Various tissue engineering methods of creating artificial scaffolds has evolved, one of thosebeing electrospinning. Electrospun scaffolds are beneficial in tissue engineering applicationsforemost in regard to their body-mimicking structure. Small pore sizes and low porosities mayhowever limit cell infiltration and thereby creation of 3D functional tissues. The issue of cellinfiltration in electrospun constructs such as nonwoven polymer scaffolds for use in tissueengineering may be solved by a method of simultaneous integration i.e. integrating particlesduring the phase of production in the electrospinning process. In this thesis investigation of aproof-of-concept to the idea of in the future distributing living cells within the threedimensionalstructure during the process of electrospinning of a polymeric biomaterial weremade. To be able to conduct simple experiments glass particles with proper sizes are used tosubstitute living cells. During this thesis a novel method called spray electrospinning tookshape enabling a fine distribution of particles in an electrospun material.The work in this thesis shows that there are methods to simultaneously integrate particles inproduction of scaffold materials, one of these composed of spraying particles whileelectrospinning on a rotating collector. The experiments were done in order to compare thedifferent methods; Double, Coaxial and Spray electrospinning pointing out similarities anddifferences between the three. The methods used to characterize the materials include scalemeasurements and SEM image analysis to determine morphology, fibre diameter, layerthickness and distance between particles. Glass particles were used as substitutes for livingcells for the sake of proof of concept which showed that these can successfully be integratedsimultaneously in an electrospun material. However porosity and the number of particles haveto be further optimized for the material to be ready for use in tissue engineering.

During electrospinning, a polymer solution becomes an electrically driven jet as it travels to a grounded plate. While the behavior of pressure-driven liquid jets has been extensively studied in fluid mechanics, none of the characteristics of fluid jet break up have been applied to electrospinning. Calculating Weber number can describe what type of breakup occurs as the polymer jet travels to the plate, which could also predict the surface morphology of electrospun fibers. Polyethylene oxide (PEO) solution was electrospun at different voltages to test whether the morphology of the electrospun fibers can be predicted through calculating Weber number. While the continuing research of electrospinning is important, the subject of electrospinning can be used as a course to teach students engineering principals over a semester. Due to the vast interdisciplinary subjects associated with electrospinning, teaching the subject as a course will give students an understanding of critical thinking skills as well as first hand accounts of research. Four weight percent PEO solution was electrospun at a range of testing parameters until the desired results were achieved, beaded or non-beaded fibers. The Weber numbers were calculated and compared to the electrospun material created. Analyzing the surface morphology revealed a beaded to non-beaded trend in nanofibers corresponding to high-to-low Weber numbers. The same trend continued for higher weight percents of PEO solutions electrospun. The course will have many learning objectives the instructor is expected to have the students achieve, building the objectives to help the students become better researchers and to learn the material. Splitting the course into three five week sections will help students understand each component of the electrospinning process, as well as fundamental engineering equations and theories. The students at the end of the semester should be able to recreate the electrospinning process on their own and create nanofibers of varying sizes. The course should also excite students about pursuing more advanced degrees in scientific fields.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

The current thrust towards the compaction of electrical power equipment, resulting in increased insulation electrical stress levels, necessitates new electrical insulating materials. In the last few decades, polymeric materials that exhibit light weight, excellent mechanical properties, low cost, and some with unique non-wetting surface characteristics, have surpassed the use of the conventional porcelain and glass insulating materials. Despite these advantages, polymeric materials are incapable of withstanding the high heat from surface arcing that is instigated by the synergism of pollution, moisture, and voltage. Surface arcing results in material loss due to heat ablation and/or the electrical tracking of polymeric materials. To overcome such issues, inorganic fillers are added to the base polymers to enhance their resistance to surface discharge activities and other performances. Since their addition can significantly reduce material costs, their use is compelling. Micron-sized fillers, here after defined as microfillers, have been used to acquire these desirable properties, but due to limitations in material processability, the further application of such fillers is limited. Consequently, nano-sized fillers, here after defined as nanofillers, have been viewed as replacements or assistant combinations to microfillers. Nanofillers are characterized by large surface areas, resulting in increased bond strengths that yield significant improvements in the various properties at fill levels well below that of microfillers. However, the primary problem of using nanofillers is their characteristic property of agglomeration due to their physical size and the forces between the fillers. Conventional mechanical mixing of nanofillers does not adequately separate the nanofillers, leading to behaviour similarly to that of microfillers. Therefore, the implementation of nanofillers is not completely effective. In chemical dispersion techniques, for example, the use of surfactants, are normally very elaborate and complicated. Due to the negative impact of agglomeration, the successful dispersion of nanofillers is pivotal in the further development of nanodielectrics for various insulation applications. In this thesis, electrospinning is proposed and realized as a new dispersal method for nanofillers in polymeric materials. This novel technique facilitates polymeric nanocomposites with improved properties due to the uniform distribution of fillers. Scanning electron microscopy (SEM) images and energy dispersive X-ray analysis (EDX) clearly indicate that electrospun nanocomposites demonstrate a better filler distribution than nanocomposites, produced by conventional mechanical mixing. Also electrospinning introduces the possibility of separating different nanofillers in different base polymers. The mechanical properties: tensile strength and hardness; the electrical properties: permittivity, tracking, and erosion resistance; and the thermal properties: thermal conductivity, thermal degradation, and heat erosion resistance of electrospun nanocomposites are compared to those of conventional nanocomposites for silicone rubber and cycloaliphatic epoxy-based polymers. All the experimental studies in this thesis confirm that electrospun nanocomposites exhibit better thermal performances than the conventional composites which are attributed to the improved distribution of the nanofillers by the newly developed electrospinning process. Also in this investigation, a two-dimensional thermal model is developed in COMSOL MultiphysicsTM by using the finite element method (FEM) to theoretically address the benefits of using nanofillers and the effects of filler dispersion. The model confirms that electrospun nanocomposites have much more uniform temperature distribution than conventional nanocomposites. This thesis presents the possible mechanisms by which nanofillers improve the heat and erosion resistance of silicone rubber nanocomposites, and also addresses the possible mechanism by which electrospinning improves nanofiller dispersion.