"In situ polymerizing hydrogel systems play an important role in many tissue engineering applications. They have proven to be useful in biomedical applications that require conversion of liquid macromer solution to tissue compliant hydrogel under physiological conditions. A series of poly(ethylene glycol)-co-poly(lactate) diacrylate macromers were synthesized with variable PEG molecular weight and lactate content. The macromer compositions were confirmed by NMR spectroscopy and ion chromatography. These macromers were polymerized to form hydrogels by free radical polymerization using either redox or photochemical initiators. The current study focused on the optimization of polymerization conditions. Compressive modulus and residual acrylate analysis were used to evaluate polymerization efficiency. To characterize the network structure, the swelling ratio values were converted to the average molecular weight between crosslinks ( ) and mesh sizes (ξ) using Flory-Rehner theory. Current study suggested hydrophobic modification is desired to achieve high polymerization efficiency. Electrospinning is a developing technique to produce ultra fine fibrous structures from polymer solutions. Current research efforts have focused on understanding the effects of principal parameters such as molecular weight distribution (MWD) and polymer surfactant interactions on the morphology of the electrospun patterns. Fundamental understanding of the dilute solution rheology of the polydisperse polymer/solvent and polymer/solvent/surfactant systems was first established. Using viscometry, the on-set of entanglement concentrations could be obtained for various systems. Electrospinning was then carried out to evaluate the effects of polymer molecular weight, molecular weight distribution (MWD) and the polymer-surfactant interaction on the fiber formation and morphological features. The importance of increased chain entanglements due to high molecular weight component within the polydisperse system and the expansion of the coil dimension by binding the surfactant micelles have been recognized. The critical concentrations for incipient as well as stable fiber formation were determined. "

The effects of fundamental solution parameters including polymer molecular weight, concentration and solvent on electrospinning of polystyrene were investigated. Each parameter was found to play a vital role in determining the morphology of beads and fibers. For dilute to semi-dilute solutions, a wide range of bead structures including wrinkled beads, cups, dishes, and toroids were observed when a volatile solvent, tetrahydrofuran, was used. Various rheological regimes where these structures may be obtained were identified. The morphological transition from bead to fiber was characterized by two critical concentrations, Ci and Cf, at which incipient and complete fibers may be observed respectively. These values were determined as a function of molecular weight. A comparison with the models proposed in the literature indicated that solvent evaporation may play an important role in jet stabilization. The fiber diameter and distribution was found to decrease significantly with molecular weight at the critical concentration, Cf. The use of N,N-dimethylformamide, a solvent with relatively high dielectric constant, also resulted in an appreciable reduction in fiber diameter and improved uniformity. The observation of solution jet evolution during the process with high speed camera (2000 frames/s) indicated that solvents have a significant influence on the jet breakdown behavior. Two types of behavior were identified based on the extent of extensional flow, bending instability, and the number of secondary jets. Solvents with high dielectric constant were found to induce extensive bending instability, which resulted in extremely fine microstructures of electrospun polymer.

For fuel cells to become commercially viable in a wider range of applications, the amount of catalyst must be reduced. One crucial area of the fuel cell assembly is the anode and cathode; these layers allow fuel and exhaust gases to diffuse, provide conduction paths for both protons and electrons, and house sites for electrocataytic reactions. Despite their multi-functionality and importance, these layers have received little attention in the way of engineering design. While Nafion and catalyst loading has been studied, the electrode layer is still considered a two-dimensional structure. By understanding the current electrode limitations, available materials, and interactions at the sites reaction sites, an intelligent, deliberate design of the anode and cathode layer can be undertaken. A three-dimensional, fibrous mat of continuous, networked proton-conducting fibers can decrease mass diffusion limitations while maintaining proton conductivity. Nafion can be formed into these types of fibers via the fabrication technique of electrospinning. By forcing a solution of Nafion, solvent, and carrier polymer through a small nozzle under high electric voltage, the polymer can be extruded into fibers with nanometer-scale diameters. The ability to control the fiber morphology lies with solution, environmental and equipment properties. In order to successfully fabricate Nafion nanofibers, we looked to both existing methodologies as well as mathematical models to try to predict behavior and fabricate our own nanofibers. Once fabricated, these mats are assembled in a membrane-electrode assembly and tested with both methanol and hydrogen as fuel, with performance compared against known data for conventional MEAs. We have been able to successfully electrospin Nafion® nanofibers continuously, creating fiber mats with fiber diameters near 400nm as verified by SEM. These mats were tested in a direct methanol fuel cell (DMFC) application as cathodes, and showed improved performance with a dilute methanol feed compared to conventional MEAs with equivalent Nafion and catalyst loading. An MEA fabricated with twin electrospun electrodes was compared against an equivalent conventional MEA, showing the same performance enhancement using a dilute methanol fuel.

Damaged cartilage can cause severe pain and restricted mobility, with few long term treatments available. The developing field of tissue engineering offers an alternative to the currently used full joint replacement. Restoring damaged cartilage through tissue engineering would enable an active lifestyle to be recovered and retained, without restrictions to joint mobility. This is increasingly important as the prevalence of osteoarthritis rises. Tissue engineering requires biomaterial scaffolds that mimic the function of the tissue while cells develop, and so the scaffold must provide the appropriate biological, chemical and mechanical stimuli. In this work, methods were developed to enable the design of scaffolds that mimic the microstructure and mechanical properties of articular cartilage. Electrospinning was investigated as a method to mimic the nanoscale collagen fibres within cartilage extracellular matrix. A parametric study was conducted to determine how changes to a gelatin solution affect the mechanical properties of the non-woven fibrous mesh. The solution properties had a clear impact on the morphology of the fibres, but the effect on the mesh mechanical properties was convoluted. The results demonstrated the need for greater understanding of the 3D morphology of electrospun meshes, to establish how these may be altered in order to design scaffolds with desirable mechanical properties. The fracture mechanics of soft materials are complex, and are generally overlooked when designing tissue engineering scaffolds. The complexities have led to a lack of standardised testing, making comparisons between studies impractical. In this work, fracture testing methods were compared, using a viscoelastic polymer to mimic some of the complexities of soft tissue mechanics. Mode III trouser tear tests and mode I pure shear tests were found to provide reliable measurements. Due to the ease of testing small samples, trouser tear testing was concluded to be the most advantageous for determining the fracture resistance of soft tissue engineering scaffolds. Finally, electrospun meshes were combined with hydrogels to create biomimetic scaffolds, which were characterised using tensile and trouser tear fracture tests. Fibre-reinforcement was shown to enhance the mechanical properties of a weak hydrogel, but diminished those of a strong, tough polyacrylamide (PAAm)-alginate hydrogel. The PAAm-alginate hydrogel exhibited mechanical properties close to those of natural articular cartilage, but without the microstructure that would enhance its suitability for use as a cartilage tissue engineering scaffold. An alternative method for reinforcing PAAm-alginate was proposed, which shows promise for producing a biocompatible scaffold that mimics both the mechanics and the microstructure of articular cartilage. Ultimately, this thesis aimed to improve the design of biomimetic scaffolds for cartilage tissue engineering, and advance mechanical characterisation techniques within this field.

Enteric pathogens form a large part of infectious diseases which contribute to a bulk of the healthcare costs. Enteric infections are usually contracted via the faecal-oral route or through contact with contaminated surfaces. Treatment by antibiotics is becoming increasingly ineffective due to the growing number of antibiotic resistant strains. Anti-microbial resistance poses a serious threat to the future of healthcare worldwide and necessitates the search for alternate forms of therapy. Bacteriophages (phages), are viruses which specifically infect and lyse bacteria. To introduce phages as a viable form of therapy, route of administration needs to be considered carefully. Model phages with broad host ranges are ideal for therapy however oral delivery to the lower gastro-intestinal (GI) poses several challenges. The acidic stomach environment can be detrimental to phages, rendering them inactive during passage. To overcome this challenge and improve the stability of phage during encapsulation and storage, this PhD research has been conducted. pH responsive polymers, Eudragit and alginate were used to develop composite microparticles which protected phage from acidic pH (pH 1-3). A novel method of acidifying oil was developed for crosslinking droplets in vitro to avoid the use of harsh solvent systems that can cause phage inactivation. Platform microfluidic technology was employed for phage encapsulation for the first time. Monodispersed droplets and particles were produced, offering fine-tuning of droplet diameter to tailor the release and pH protection of encapsulated phage. Process scale-up was attempted using membrane emulsification (ME) to produce larger volumes of encapsulated phage. In vitro and in-situ models investigated the efficacy of encapsulated phage-bacterial killing. Industrial scale method of spray drying, and electrospinning were also used to demonstrate the versatility of the formulation. Tableting dry powder phage, showed an effective method for producing solid dosage forms for therapy. Additionally, electrospun phage fibres also showed the potential use of pH responsive formulations in addressing wound infections. Improvement in encapsulated phage storage stability was observed with the addition of trehalose in the formulation. This research underpins the need for testing phage encapsulation for site-specific delivery and offers insight into the potential use of commercially available technologies.

The production of cellulose derived hybrid carbon nanofibre (CNF)/carbon nanotubes (CNTs) electrodes for the fabrication of supercapacitors and carbon fibre composites was investigated. The CNTs were grown via a floating catalyst chemical vapor deposition (CVD) method on the top surface of electrospun cellulose derived CNFs. These CNF and CNF/CNTs samples were then used as electrodes to produce liquid electrolyte-based supercapacitors. The growth of CNTs leads to an improvement of electrochemical performance compared to the plain CNFs. This improvement is due to the grown CNTs enlarging the reactive sites through enhanced surface area and porosity, and thereby increasing the conductivity of the system. CNTs have been also grown onto CNFs containing ferrocene and SiC particles. Composites were fabricated by combining the fibres and CNTs grown fibres with model polymers. The stress transfer properties of these materials have been estimated using an in situ Raman spectroscopic method by observing the shift of the Raman band during the tensile deformation of model polymer composites. Using this method, the elastic modulus of CNF/SiC/CNTs fibres has been estimated to be 208 ± 26 GPa. No shifts in the peak positions of bands relating to the carbon structure were obtained for in situ Raman spectroscopic studies of the CNF/CNTs fibres made from the ferrocene embedded fibres. This was thought to be due to the low yield of CNTs on the surface of the fibres. Furthermore, CNF/CNTs electrode-based structural supercapacitors, combining a solid electrolyte with the carbonized fibres, have been produced. These CNF/CNTs electrodes have a better capacitive performance than the plain CNF electrodes. There was a decrease in this performance with increased curing time of the resin, from 2 to 24 h, due to a lack of charge carrier mobility in the latter samples. A Raman spectroscopic study of the deformation of the carbon structures showed that the G-band shift towards a lower wavenumber position for the CNF and CNF/CNTs samples processed at a carbonization temperature of 2000 °C. Moduli of these fibres were estimated to be ~145 GPa and ~271 GPa, respectively, suggesting the growth of CNTs not only enhances the capacitive performance but also the mechanical properties of the structural supercapacitors. No Raman bend shift was found for the CNFs and CNF/CNTs samples processed below a carbonization temperature of 2000 °C, e.g. 900 °C and 1500 °C. This is because the graphitic structures are not well developed at carbonization temperatures below 1500 °C.

Electrospinning produces submicron fibers from a wide range of polymer/solvent systems that enable a variety of different applications. In electrospinning process, a straight polymer/solvent charged jet is initially formed, followed by a circular moving jet in the shape of a cone, called the bending region. The process physics in the bending region are difficult to study since the jet diameter cannot be measured directly due to its rapid motion and small size (~microns and smaller), and due to complex coupling of multiple forces, mass transport, and changing jet geometry. Since the solutions studied are hydrophilic, they readily absorb ambient moisture. This thesis explores the role of the bending region in determining the resulting electrospun fiber diameter through a combined experimental and modeling analysis for a variety of hydrophilic polymer/solvent solutions. Electrospinning experiments were conducted over a broad range of operating conditions for 4 different polymer/solvent systems. Comparison of the final straight jet diameters to fiber diameters reveals that between 30% to 60% jet thinning occurs in the bending region. These experiments also reveal that relative humidity significantly affects the electrospinning process and final fiber diameter, even for non-aqueous solutions. A model is developed to obtain insight into the bending region process physics. Important ones include understanding the mass transport for non-aqueous hydrophilic jets (including solvent evaporation and water absorption on the jet surface, radial diffusion, and axial advection), and the coupling between the mass and force balances that determines the final fiber diameter. The absorption and evaporation physics is validated by evaporation experiments. The developed model predicts fiber diameter to within of 8%, even though the solution properties and operating conditions that determines net stretching forces and net evaporation rates vary over a large range. Model analysis reveals how the net evaporation rate affects the jet length and net stretching force, both of which ultimately determine the fiber diameter. It is also shown that the primary impact of RH on the process is through occupation of the surface states that limits solvent evaporation rate, rather than the amount of water absorbed. Correlation functions between process conditions, solution properties and the resulting fiber diameters are discussed.

Spider-silk is known as one of the stronger natural materials, unfortunately it is impossible to farm spiders due to their territorial and cannibalistic nature. To address this issue, researchers have studied spider-silk to discover how it is produced in nature. From their results, spider-silk is composed of large sized proteins produced in two different cell types. Using this knowledge, researchers created transgenic organisms capable of producing spider-silk proteins in large quantities. Using these proteins, several groups have created fibers, films, hydrogels, and adhesives with robust and versatile properties. Wet-spinning is a technique commonly used to create fibers from spider-silk proteins. These fibers unfortunately do not compare to the mechanical properties of natural silk. To address this researchers have used a method known as electrospinning to create spider-silk fibers with substantially smaller diameters. In doing so, these electrospun fibers have increased surface area and enhanced mechanical properties. Using this method, our group has modified the electrospinner to be able to produce continuous fine diameter yarns composed of hundreds of nanofibers with mechanical properties surpassing that of natural silk. Fibers aside, spider-silk proteins can be used to create a variety of different biocompatible materials. To further enhance these materials, our group has utilized a technique traditionally used for observation. This technique employs a high intensity light source to initiate cross-links within the proteins. With this method, our spider-silk protein materials have increased their mechanical properties by a factor of seven. These materials can further be modified through post-treatments, resulting in tunable materials with diverse and robust mechanical properties.

Assessing the sustainability of nanomanufacturing products and processes has been difficult to achieve using conventional approaches mainly due to an inadequate inventory, large process-to-process variation, and a dearth of relevant toxicology data for nanomaterials. Since these issues are long term in nature, it is required to create hybrid methodologies that can work towards filling the existing gaps. Merging thermodynamic techniques such as the exergy analysis with environmental assessments can help make better, more informed choices while providing an opportunity for process improvement by enabling to correctly quantify efficiency loss through the waste stream, and by locating the exact areas for improvement. A preliminary technique that utilizes environmental assessment feedback during the process design along with an exergy analysis is presented. As a test case, an environmental assessment aided by an exergy analysis was carried out on the electrospinning process for producing polyvinylidene fluoride nanofibers. The areas of greatest concern, both from an environmental as well as a thermodynamic point of view, have been found to be the high energy consumption and the complete loss of solvent during the process of electrospinning. Interestingly, exergy consumption is significantly higher for fibers with a smaller (

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 %.