Antibacterial agent delivery is of great importance in medicine and dentistry since the bacterial infections are still one of the major reasons for hospitalization and mortality. Despite of the development of technique and pharmacy, more antimicrobial agents are optimized and utilized to treat infections, and their action of principal is better understood which lay a foundation for developing strategies for infection treatment. Over the last decades, many delivery systems have been established to deliver bacterial agents and maintain a sustained activity against them. However, the bacteria are always developing and finding a way to defend themselves. A more responsive antibacterial agent delivery system, which can release the active substances on demand to match the stages of diseases, is highly desirable. Therefore, it motivates us to carry out the work to develop a multifunctional delivery system for antibacterial particle formulation and encapsulation based on the layer-by-layer self-assembly technique and electrospinning, to manipulate the release with external triggers, such as near-infrared (NIR) light and alternating magnetic field (AMF). Strategically, two different kinds of antibacterial agents, chlorhexidine and doxycycline, were studied. Chlorhexidine was fabricated into spherical particles and functionalized with both gold and magnetite nanoparticles, and doxycycline was encapsulated within microcapsules which were also functionalized with magnetite nanoparticles. Their release kinetics and possibilities to trigger the release with either a NIR light or AMF was explored. The first two chapters of the thesis give a general introduction and literature review on the current use of antibacterial agents and the problems concerned, strategies already developed for antibacterial agent delivery, and the potential triggers to induce a smart release. In chapter 3, a brief description of materials and methods, and instruments is presented. Chapter 4 is about chlorhexidine particle formulation. Firstly, particulation of chlorhexidine and mechanism of 4 spherical interconnected structure formation was explored, and then the chlorhexidine particles are encapsulated either by LbL assembly or spray-drying. The chlorhexidine spheres were also functionalized with gold nanorods and Fe3O4 nanoparticles to achieve NIR light and magnetic field manipulated release, and the effect of nanoparticles on the formation of chlorhexidine spheres was also studied. When the chlorhexidine particles were incorporated into electrospun fibers, a sustained antibacterial activity was demonstrated. Chapter 5 is about the delivery of doxycycline to cells with microcapsules and the sustained intracellular doxycycline activity was demonstrated via EGFP expression when the cells were engineered with a tetracycline regulated gene expression system. Intracellular triggered release and upregulation of EGFP expression was achieved by an AMF. The results successfully demonstrated the possibility of chlorhexidine and doxycycline delivery and NIR light/AMF triggered release, which is promising for a future application in medicine and dentistry.

The fundamental structure of all biological membranes is the lipid bilayer. At- tributed to the multifaceted features of lipids and its dynamical interaction with other membrane-integrated molecules, the lipid bilayer is involved in a variety of physiological phenomena such as transmembrane transportation, cellular signalling transduction, energy storage, etc. Due to the nanoscale but high complexity of the lipid bilayer system, experimental investigation into many important processes at the molecular level is still challenging. Molecular dynamics (MD) simulation has been emerging as a powerful tool to study the lipid membrane at the nanoscale. Utilizing atomistic MD, we have quantitatively investigated the effect of lamellar and nonlamellar lipid composition changes on a series of important bilayer properties, and how membranes behave when exposed to a high-pressure environment. A series of membrane properties such as lateral pressure and dipole potential pro les are quanti ed. Results suggest the hypothesis that compositional changes, involving both lipid heads and tails, modulate crucial mechanical and electrical features of the lipid bilayer, so that a range of biological phenomena, such as the permeation through the membrane and conformational equilibria of membrane proteins, may be regulated. Furthermore, water also plays an essential role in the biomembrane system. To balance accuracy and efficiency in simulations, a coarse-grained ELBA water model was developed. Here, the ELBA water model is stress tested in terms of temperature- and pressure-related properties, as well as hydrating properties. Results show that the accuracy of the ELBA model is almost as good as conventional atomistic water models, while the computational efficiency is increased substantially.

Intermittent nature of renewable energy sources like the wind and solar energy poses new challenges to harness and supply uninterrupted power for consumer usage. Though, converting energy from these sources to useful forms of energy like electricity seems to be promising, still, significant innovations are needed in design and construction of wind turbines and PV arrays with BS systems. The main focus of this research project is mathematical modelling and control of wind turbines, solar photovoltaic (PV) arrays and battery storage (BS) systems. After careful literature review on renewable energy systems, new developments and existing modelling and controlling methods have been analysed. Wind turbine (WT) generator speed control, turbine blade pitch angle control (pitching), harnessing maximum power from the wind turbines have been investigated and presented in detail. Mathematical modelling of PV arrays and how to extract maximum power from PV systems have been analysed in detail. Application of model predictive control (MPC) to regulate the output power of the wind turbine and generator speed control with variable wind speeds have been proposed by formulating a linear model from a nonlinear mathematical model of a WT. Battery chemistry and nonlinear behaviour of battery parameters have been analysed to present a new equivalent electrical circuit model. Converting the captured solar energy into useful forms, and storing it for future use when the Sun itself is obscured is implemented by using battery storage systems presenting a new simulation model. Temperature effect on battery cells and dynamic battery pack modelling have been described with an accurate state of charge estimation method. The concise description on power converters is also addressed with special reference to state-space models. Bi-directional AC/DC converter, which could work in either rectifier or inverter modes is described with a cost effective proportional integral derivative (PID/State-feedback) controller.

Thesis (Ph. D.)--University of Michigan. / eContent provider-neutral record in process. Description based on print version record.

Thesis (Ph. D.)--University of Michigan.

This thesis is concentrated on the long-term fracture of thick unidirectional glass and carbon fibre composites subjected to transverse stress. The objective was to develop a methodology for predicting the long term lifetime of a composite rotor used as part of a flywheel based energy storage system. The flywheel design is based on accommodating high hoop stresses induced during the high speed rotation. However, the different Poisson's ratios of the constituent materials in the rotor result in a complex stress distribution with significant stresses introduced in a direction transverse to the fibres. The possibility has been raised that the lifetime of the rotor will be limited by crack growth in this transverse direction, originating from defects (pores, cracks etc) that can be introduced into the rotor during its manufacture. The approach explored in this work has been to adopt a fracture mechanics based methodology whereby the rate of crack growth in a thick composite is measured as a function of an applied stress intensity. The basic fracture parameters for the material were measured such that the time taken for a crack to grow to a size sufficient to cause failure under an operating stress could be calculated. The materials were also examined to characterise the nature, size and extent of inherent defects. The stress distribution in the rotor under operating conditions was modelled using finite element analysis. The combination of information on inherent defects, stress directions and crack growth rates enable predictions to be made concerning the likely lifetime of the composites. Proof stress diagrams were also constructed in order to demonstrate an approach to product quality assurance testing. The end point of the work was to identify critical manufacturing defect sizes that could be tolerated under the specified operating conditions. The methodology developed for lifetime predictions was critically assessed and considered to be generally acceptable. The work did however raise some concerns regarding the applicability of a conventional fracture mechanics approach applied to heterogeneous composite systems where the size of the cracks are very small. It is recommended that future work should concentrate on studying this area with an emphasis on crack nucleation studies rather than on further crack propagation work.

This thesis aims to challenge the conventional assumption about the irreversibility of the decline of the textile industry in developed countries. It is argued that the decline can be reversed if mature textile firms can break away from their traditional routines and practices and radically and continuously change their technologies, markets and organisational structure to adapt to the rapidly changing business environment. Using the European textile industry as a case study, this thesis shows that a number of European countries, including Germany and The Netherlands, have managed to bypass the maturity-trap -a phenomenon commonly found in large mature firms because of an inability to adapt to changing external conditions- through industrial reconfiguration from the 1960s onwards. The majority of the industry, however, has been in relative decline over the past decade as the market has become much more competitive and consequently made their old strategies obsolete. Under such circumstances there is an urgent need to turn the industry around. Learning from the failure of the Courtaulds (UK) and the success of Ten Cate (NL) and Freudenberg (DE), the thesis illustrates how the maturity-trap can take hold and how the process of de-maturity can be initiated at the firm level. The case study of Marzotto highlights how the danger of the maturity-trap is now no longer just a British phenomenon. This once highly successful firm is now in great danger of falling into the maturity-trap. The issue at stake is the long-term survival of the European textile industry and how rapidly its long-term competitiveness can be restored.

The thesis aims at investigating the connection between nucleus mechanical characteristics with pluripotency state and differentiation associated with altered cell gene expression levels. The project investigates the deformation characteristics of the cell nucleus during unconfined compression in a 3D cell-seeded agarose constructs. The studies report modification in the mechanical behaviour of the nucleus in different embryonic stem cell phenotypes based on various pluripotent states (naïve or primed states) or following triggering of early differentiation. A multi-scale model is also presented to simulate dynamic details of mechanical perturbation to cells during compression. The first chapter presents a review of the relevant literature to introduce current progress in the related research field and the second chapter describes the general methods used in the thesis including cell culture, agarose construct preparation, construct compression and microscopy recording. The third chapter presents findings of studies involving the application of compression to embryonic stem cells in naïve and primed sate within agarose scaffolds. A range of parameters relating to the relative cell/nucleus morphological modifications are recorded with analysis and discussion. Chapter four presents studies that investigate the early differentiation of embryonic stem cells from either the naïve and primed pluripotency, achieved by altering cell culture condition, and further reveals the nuclear mechanical characteristic changes. The fifth chapter describes a multi-scale model developed to simulating the 3D cell-seeded agarose compression reported in previous chapters. This model is also used to estimate cell mechanical parameters and show accurate deformation detail in different locations within the construct. A final discussion of the thesis is provided in chapter 6 with a plan for future work.

Touch is one of the less exploited sensory channels in human machine interactions. While the introduction of the tactile feedback would improve the user experience in several fields, such as training for medical operators, teleoperation, computer aided design and 3D model exploration, no interfaces able to mimic accurately and realistically the tactile feeling produced by the contact with a real soft object are currently available. Devices able to simulate the contact with soft bodies, such as the human organs, might improve the experience. The existing commercially available tactile displays consist of complex mechanisms that limit their portability. Moreover, no devices are able to provide tactile stimuli via a soft interface that can also modulate the contact area with the finger pad, which is required to realistically mimic the contact with soft bodies, as needed for example in systems aimed at simulating interactions with virtual biological tissues or in robot-assisted minimally invasive surgery. The aim of this thesis is to develop such a wearable tactile display based on the dielectric elastomer actuators (DEAs). DEAs are a class of materials that respond to an electric field producing a deformation. In particular, in this thesis, the tactile element consists of a so-called hydrostatically coupled dielectric elastomer actuator (HC-DEAs). HC-DEAs rely on an incompressible fluid that hydrostatically couples a DEA-based active part to a passive part interfaced to the user. The display was also tested within a closed-loop configuration consisting of a hand tracking system and a custom made virtual environment. This proof of concept system allowed for a validation of the abilities of the display. Mechanical and psychophysical tests were performed in order to assess the ability of the system to provide tactile stimuli that can be distinguished by the users. Also, the miniaturisation of the HC-DEA was investigated for applications in refreshable Braille displays or arrays of tactile elements for tactile maps.

Bio-composite hierarchical materials have attracted the interest of the academic community operating in the field of bio-inspired materials for their outstanding mechanical properties achieved via lightweight structural designs. Antler and mantis shrimp's cuticle are extreme examples of materials naturally optimised to resist impacts and bear dynamic loading. Firstly, a class of finite-element fibril models was developed to explain the origin of heterogeneous fibrillar deformation and hysteresis from the nanostructure of antler. Results were compared to synchrotron X-ray data and demonstrated that the key structural motif enabling a match to experimental data is an axially staggered arrangement of stiff mineralised collagen fibrils coupled with weak, damageable interfibrillar interfaces. Secondly, the cuticle of the crustacean Odontodactylus scyllarus, known as peacock mantis shrimp, was investigated. At the nanoscale it consists of mineralised chitin fibres and calcified protein matrix, which form plywood layers at the microscale. Lamination theory was used to calculate fibrillar deformation and reorientation and, in addition, an analytical formulation was used to decouple in-plane fibre reorientation from diffraction intensity changes induced by 3D lamellae tilting. This animal also attracted my attention for using its hammer-like appendages to attack and destroy the shells of prey with a sequence of two strikes. Inspired by this double impact strategy, I performed a set of parametric finite-element simulations of single, double and triple mechanical hits, to compute the damage energy of the target. My results reveal that the crustacean attack strategy has the most damaging effect among the double impact cases, and lead me to hypothesise, that optimal damaging dynamics exists, depending on the sequence of consecutive impacts and on their time separation values. These new insights may provide useful indications for the design of bio-inspired materials for high load-bearing applications.