Nanofibres are useful in a broad range of applications in areas such as medical science, food science, materials engineering, environmental engineering, and energy and electronics due to their outstanding characteristics: their small size, high surface-to-volume ratio, high porosity, and superior mechanical performance. Recently, controlled drug delivery systems have gained significant attention, especially with respect to the use of polymer nanofibres. For these systems, the ability to control of the length of the polymer nanofibre is important because the amount of drug released depends on the length of the fibre. Electrospinning is the simplest and most cost-effective method of fabricating polymer nanofibres. In the process, a high voltage is used to create an electrified jet which will eventually become a nanofibre. The electrified jet ejects when a high voltage is applied to the electrospinning setup. On the other hand, the jet does not eject when the applied voltage is below the threshold voltage. It is therefore possible to fabricate and chop nanofibres by controlling the values of the voltages applied and a special high-voltage pulsed power supply has been developed for this purpose. In this research, an IGBT-based pulsed power supply has been designed and built to be used for non-continuous-mode electrospinning. The IGBTs are connected in series to deliver high voltage pulse voltages to an electrospinning setup. The IGBT-based pulsed power supply is capable of producing controllable square pulses with a width of a few hundred microseconds to DC and amplitudes up to 10 kV. The technique of non-continuous-mode electrospinning was tested using the pulsed power supply designed in this work. The new system was able to fabricate and chop nanofibres with PEO and alginate/PEO solutions. It was concluded that the minimum pulse width that can initiate an electrified jet is approximately 80 ms for the parameters used in this study. A longer period produces a more constant jet during the pulse-on voltage when the duty ratio is the same value. It is also highly likely that a jet is always ejected during the pulse-on voltage when the duty ratio is more than 40 %.

<p>Continuous nanostructures, such as electrospun nanofibers, embedded with proteins may synergistically present the topographical and biochemical signals to cells for tissue engineering applications. In this dissertation, co-axial electrospinning is introduced as a mean to efficiently encapsulate and release protein and live entities while producing a tissue engineering scaffold with uniaxial topography. In the first specific aim, aligned poly (caprolactone) nanofibers encapsulated with BSA and growth factors were produced to demonstrate controlled release and bioactivity retention properties. Control over release kinetics is achieved by incorporation of poly(ethylene glycol) as a porogen in the shell of the fibers. PEG leaches out in a concentration and molecular weight dependent fashion, leading to BSA release half-lives that range from 1 -20 days. The second specific aim introduces the fabrication of virus and bacterial cell encapsulated electrospun fibers to achieve unique biological functionalization. Adenovirus encoding the gene for green fluorescent protein was efficiently encapsulated into the core of poly(caprolactone) fibers through co-axial electrospinning and subsequently released via the porogen-mediated process. Encapsulated bacterial cells were confined to fibers of varying core sizes, which provided an aqueous core environment for free mobility and allowed the bacterias to proliferate within the fibers. </p><p>In the third specific aim, the differentiation of skeletal myoblasts on aligned electrospun polyurethane fibers and in the presence of electromechanical stimulation were systematically studied. Skeletal myoblasts cultured on aligned polyurethane (PU) fibers showed more pronounced elongation, better alignment, upregulation of contractile proteins and higher percentage of striated myotubes compared to those cultured on random PU fibers and film. In the last specific aim, the controlled release aspect of co-axial electrospun fibers were combined with skeletal tissue engineering to serve as a therapeutic implant for the treatment of hemophilia. A non-viral, tissue engineering approach were taken to stimulate local lymphatic or vascular system in order to enhance transport near the FVIII-producing implants to provide effective and sustained treatment for hemophilia A. Stable FVIII-producing clones were engineered from isolated myoblasts and cultured on aligned, protein-releasing electrospun fibers to form skeletal myotubes. The implanted construct rapidly integrated with host tissue and selectively induced angiogenesis or lymphangiogenesis as a result of the encapsulated growth factors. Constructs inducing angiogenesis significantly enhanced the transport of produced FVIII and achieved hemophilia phenotypic correction over two months. The use of co-axial electrospun fibers to serve as controlled delivery and tissue engineering construct furthers the continued pursue of a more sophisticated and medically relevant implant scaffold design.</p> / Dissertation

Uniform and aligned nanofibers have been obtained by eletrospinning. Activated carbon nanofibers (ACNFs) have been used as electrode materials for battery and electric double layer due to its porous properties. A high value of surface area can be attained (1000 - 3000 nm) by activation, due to the presence of micropores on the surface of nanofibers. A series of nanofibers have been prepared using different polymer precursors and concentrations by electrospinning in this study. Morphological study by SEM reveals a uniform and aligned fibrous structure for the PAN-based CNF (11 wt%) and a curved and twisted fibrous structure for the PAN-based CNF (8 wt%) and the acrylic-based CNF (9 wt%). Thus, the microstructure of CNF can be greatly influenced by the concentration of polymer precursor; high quality of nanofibers can be produced with higher polymer concentration and higher viscosity. The diameter of PAN-based nanofibers is gradually decreased from 400 to 200 nm during stabilization, carbonization, and activation, due mainly to the degradation and condensation. Surface of CNF becomes rough after activation due to the etching by potassium ions at high temperatures. Microstructural study by X-ray diffraction and Raman spectroscopy indicates a discernible diffraction peak at d002 = 0.356 nm and the ratio ID/IG = 1.83 of ACNFs, showing an amorphous and disordered structure, and leading to a low conductivity. Adsorption/desorption isotherms obtained from BET measurements under nitrogen atmosphere suggests a relatively small surface area of 8-10 m2/g, indicating that there might be no adsorption on the porous ACNF or the porous structure has been destroyed after carbonization. This leads to a relatively low conductance of 17 Faraday/g measured from the cyclic voltammetry.

In the recent years, researchers have discovered a multitude of applications using nanofibers in fields like composites, biotechnology, environmental engineering, defense, optics and electronics. This increase in nanofiber applications needs a higher rate of nanofiber production. Electrospinning has proven to be the best nanofiber manufacturing process because of simplicity and material compatibility. Study of effects of various electrospinning parameters is important to improve the rate of nanofiber processing. In addition, several applications demand well-oriented nanofibers. Researchers have experimentally tried to control the nanofibers using secondary external electric field. In the first study, the electrospinning process is modeled and the bending instability of a viscoelastic jet is simulated. For this, the existing discrete bead model is modified and the results are compared, qualitatively, with previous works in literature. In this study, an attempt is also made to simulate the effect of secondary electric field on electrospinning process and whipping instability. It is observed that the external secondary field unwinds the jet spirals, reduces the whipping instability and increases the tension in the fiber. Lattice Boltzmann method (LBM) has gained popularity in the past decade as the method is easy implement and can also be parallelized. In the second part of this thesis, a hybrid numerical scheme which couples lattice Boltzmann method with finite difference method for a Oldroyd-B viscoelastic solution is proposed. In this scheme, the polymer viscoelastic stress tensor is included in the equilibrium distribution function and the distribution function is updated using SRT-LBE model. Then, the local velocities from the distribution function are evaluated. These local velocities are used to evaluate local velocity gradients using a central difference method in space. Next, a forward difference scheme in time is used on the Maxwell Upper Convected model and the viscoelastic stress tensor is updated. Finally, using the proposed numerical method start-up Couette flow problem for Re = 0.5 and We = 1.1, is simulated. The velocity and stress results from these simulations agree very well with the analytical solutions.

Electrospinning is a technique to achieve nanometer scale fibers. Similar to the conventional spin methods of making fabric, the viscous polymer solution is ejected from a spinneret; stretched and solidified in the air, the solution forms the fibers. The different part of electrospinning among others is that the fibers are driven by the electrostatic force, which induces the repulsion inside the liquid and further reduces the diameter. The resultant product is a non-woven membrane, which is porous; and the pore size is around several nanometers to a micrometer wide. In this work, the relationship between the diameter of electrospun silica fibers, experimental parameters such as concentration and voltage, and between pore size of the fiber membrane and experimental time were studied. Materials used in the process are Polyvinylpyrrolidone (PVP), butanol and spin-on-glass coating solution, which act as polymer carrier, solvent, and silica-precursor, respectively. Polymer/silica precursor composite fibers were ejected from the needle of a plastic syringe when an electrical field, as high as several kV/cm, was applied. Then silica fibers were achieved by baking the composite ones at 773 oK for 12 h. Electrospun silica nanofibers were characterized as a function of polymer solution parameters. The calcined fibers were examined by using a field emission scanning electron microscope. The results showed that the fiber diameters decrease with decreasing proportion of polymer and silica precursor, and increase with a higher electric field. Pore sizes, defined as the grid areas enclosed by fibers on nearby layers, were also examined and showed no time-dependent tendency when the electrospin time was between 1-5 min. Fiber membranes were then used as the platform for protein detection. The results were compared with the control, which used glass slides as the platform. The results make it possible to make a more sensitive biosensing device.

An amperometric glucose biosensor was fabricated using electospun polyaniline fibers. Polyaniline was reacted with camphorsulfonic acid to produce a salt, which was then dissolved in chloroform containing polystyrene. Using this solution, fibers were formed and collected by electrospinning. Glucose oxidase was immobilized onto these fibers using an electrostatic layer-by-layer adsorption technique. In this method, poly(diallyldimethylammonium chloride) was used as the counter ion source. The level of adsorption was examined and evidence of layer-by-layer adsorption was obtained using a quartz crystal microbalance technique. A biosensor was fabricated from these fibers as a working electrode, and used to measure the glucose concentration accurately.

Thesis (Ph.D.)--University of Wollongong, 2009. / Typescript. Includes bibliographical references.

Attrition rates for anticancer drugs are much higher than any other therapeutic area. Only 5%#37; of the agents that demonstrate anticancer activity in the preclinical stages of development demonstrate clinical efficacy in phase III trials. This high attrition rate becomes alarming when we consider that the cost of research and development can amount to 1 billion dollars. To exacerbate this problem, many new cancer drugs are being discontinued, withdrawn or suspended. The reasons for this high attrition rate are complex and may be partly attributed to suboptimal preclinical strategies such as the use of two-dimensional (2D) cell culture systems to evaluate new agents during the development and testing stages. Cancer cells cultured in 2D do not mimic the complexity of the three-dimensional (3D) milieu of tumors in vivo. There is overwhelming evidence that in vitro 3D culture systems more accurately reflect the tumor microenvironment and present better predictive value for assessing the efficacy of new chemotherapeutic agents. The development of 3D culture systems for anticancer drug development remains an unmet need. Despite progress, a simple, rapid, scalable and inexpensive 3D-tumor model that recapitulates in vivo tumorigenesis is lacking. Herein, we report on the development and characterization of a 3D nanofibrous scaffold produced by electrospinning a mixture of poly(lactic-co-glycolic acid) (PLGA) and a block copolymer of polylactic acid (PLA) and mono-methoxy polyethylene glycol (mPEG) designated as 3P. Cancer cells cultured on the 3P scaffold formed tight aggregates similar to in vivo tumors, referred to as tumoroids that depended on the topography and net charge of the scaffold. 3P scaffolds induced tumor cells to undergo the epithelial-to-mesenchymal transition (EMT) as demonstrated by up-regulation of vimentin and loss of E-cadherin expression. 3P tumoroids showed higher resistance to anticancer drugs than the same tumor cells grown as monolayers. Inhibition of ERK and PI3K signal pathways prevented EMT conversion and reduced tumoroid formation, diameter and number. Fine needle aspirates, collected from tumor cells implanted in mice when cultured on 3P scaffolds formed tumoroids, but showed decreased sensitivity to anticancer drugs, compared to tumoroids formed by direct seeding. These results show that 3P scaffolds provide an excellent platform for producing tumoroids from tumor cell lines and from biopsies and that the platform can be used to culture patient biopsies, test for anticancer compounds and tailor a personalized cancer treatment.

Flame retardant (FR) intumescent additives and montmorillonite (MMT) organoclay incorporated nylon-6 nanocomposite (FR-NC-PA6) fibers with a diameter of about 200 nm were fabricated by electrospinning. Before electrospinning, dispersion and exfoliation of the FR additive and MMT in nylon-6 were achieved by twin-screw extrusion. Tensile, TGA and UL-94 flammability tests were first performed using injection-molded bulk samples. The tensile modulus of FR-NC-PA6 was 45% higher than that of neat PA6, but tensile strength and elongation at break decreased by 23% and 98.7%, respectively. It is worth noting that although the TGA results show that FR-NC-PA6 has a slightly earlier decomposition temperature than neat PA6, it did not drip under fire and had the best rating (V-0) in UL 94 test, while neat PA6 is only rated as V-2. SEM and EDX of char residues after the UL 94 test clearly show the oxygen-rich protective char layer on the surface. These results indicate the advantage of using clay and FR additive in bulk-form PA6. Flammability of electrospun nanocomposite fibers was characterized by Micro-combustion calorimeter (MCC), a small-scale test to screen flammability of polymer materials. The MCC results show that the nano-fillers in both bulk and fiber form could effectively improve flame retardant properties of the material. Electrospun fibers had similar combustion properties as bulk materials. In addition to FR applications, superhydrophobic surface was another area that was explored using the electrospun nanocomposite fibers. Static water contact angle (WCA) test showed that samples with 5wt% clay even without plasma treatment greatly improved the WCA to 140°, probably due to the barrier effect of nanoclay platelets. Plasma treatment was used to modify the surface energy, further improving WCA to as high as 160°. However, fiber structure was partially etched away when overexposed to the plasma. This etching effect increased the surface roughness. Clay incorporated samples had higher level of surface roughness and better resistance to plasma etching compared to neat nylon 6. / text

This research work focuses on single wall carbon nanotube (SWNT)/polymer composites and novel structured electrospun polymer materials. Poly (methyl methacrylate) (PMMA) is used as polymer matrix. Obtaining SWNT/PMMA composite with enhanced mechanical and electrical properties is one of the research goals. The first important step is to figure out a method for achieving uniform SWNT dispersion in PMMA. Eight different solvents were used to disperse SWNT in PMMA. It is found that the polar component of the solubility parameter (£_p) of the solvent affects SWNT dispersion in PMMA. SWNT dispersion in PMMA improves with increasing solvent Ôp value, and the most uniform dispersion is obtained in nitromethane, which is the most polar solvent employed in this study. SWNT/PMMA composite films at various SWNT concentrations were processed employing nitromethane as the solvent. Mechanical and electrical property enhancements are observed. Processing, structure, morphology, and properties of these composites are discussed. A comparison between reinforcement efficiency of SWNT, multiwall carbon nanotubes (MWNT), and vapor grown carbon nano fibers (VGCNF) in PMMA is also discussed. In order to electrospin SWNT/PMMA/nitromethane solution into composite nanofibers successfully, first PMMA was electrospun. With increasing solution concentration, morphology of the electrospun polymer changed from particles to fibers. At relatively low solution concentrations, micro- and nano-structured polymer particles, and at higher solution concentrations, porous and solid nanofibers are observed. SWNT/PMMA/nitromethane solution was electrospun into polymer shell-SWNT core nanofibers. Solvent characteristics play an important role on particle or fiber mat morphology. The qualitative relationship between solvent properties (evaporation rate, dielectric constant, surface tension, and viscosity) and particle morphologies is discussed. By tailoring solution properties and electrospinning conditions, one can produce particles or fibers with controlled morphology for specific applications.