Bone diseases such as osteoporosis and rickets cause significant reduction in bone quantity and quality, leading to mechanical abnormalities. While the reduction of bone quantity can be assessed using clinical tools like DXA and pQCT, there is little quantitative knowledge of how altered bone quality in diseased bone increases fracture risk. There is a clear need to develop high-resolution diagnostic techniques to close the gap between onset of fracture relevant changes and diagnosis. Here, a functional imaging technique (in situ synchrotron X-ray imaging with micromechanics) was developed to measure alterations in fibrillar deformation mechanisms in rickets, glucocorticoid-induced osteoporosis (GIOP), and premature ageing. During applied loading, percentage shifts in Bragg peak positions arising from the meridional collagen stagger, measured from the small angle X-ray scattering (SAXS) patterns, give fibrillar level strain as a function of applied stress in real time. To link nanostructural changes to altered fracture risk and deformability, well defined animal (mouse) models created via N-ethylnitrosurea mutagenesis were used. The fibril modulus, maximum fibril strain and fibril-to-tissue strain ratio were determined, complemented by quantitative backscattered scanning electron microscopy and microcomputed tomography to measure microscale mineralisation. A significant reduction of fibril modulus and enhancement of maximum fibril strain was found in rickets and GIOP mice. A significantly larger fibril strain/tissue strain ratio was found in GIOP mice compared to wild-type mice, indicative of a lowered mechanical competence at the bone matrix level. The effects of altered in vivo muscular force distributions on the skeletal system in rickets were measured using position resolved scanning SAXS. Increase of mineral nanoplatelet alignment is observed in wild-type mice near zones of large in-vivo muscle force but not in rachitic mice. These results demonstrate the ability of synchrotron-based in situ X-ray nanomechanical imaging to identify functional alterations in nanoscale bone quality in metabolic bone diseases.

Development of thermoelectric materials to date has focused on materials that can operate at lower temperatures. However; there is now an increased need to develop materials for higher temperature applications. In this research, medium to high temperature oxide and non-oxide thermoelectric materials were fabricated and characterized. For oxide thermoelectric materials, La4Ti4O14 and Sr4Nb4O14 were chosen. These compounds are members of the homologous A4B4O14 series and possess perovskite-like layered structure (PLS). PLS compounds have low thermal conductivity due to a layered structure compared to the perovskite materials (e.g. SrTiO3). These atomic scale layers help to reduce the thermal conductivity of PLS compounds. Doping in PLS materials also creates atomic scale disorders. The effect of acceptor-donor doping and oxidation-reduction on the thermal conductivity of PLS ceramics were investigated in relation to mass contrast and compositional non-stoichiometry. High resolution TEM and XPS revealed that acceptor doping of La4Ti4O14 produced nanoscale intergrowth regions of n=5 layered phase inside n=4 layered phase, while donor doping produced nanoscale intergrowth regions of n=3 layered structure. As a result of these nanoscale intergrowths, the thermal conductivity value reduced by ~ 20% compared to the theoretical value. Pure La4Ti4O14 has a thermal conductivity value of ~ 1.1 W/m.K which dropped to a value of ~ 0.98 W/m.K in Sr doped La4Ti4O14 and ~ 0.93 W/m.K in Ta doped La4Ti4O14. Pure Sr4Nb4O14 has a thermal conductivity value of ~ 1.05 W/m.K which dropped to ~ 0.6 W/m.K after La doping. The factors influencing the thermal conductivity of PLS compounds were also discussed.For non-oxide ceramics, CoSb3 was chosen due to its cage-like structure and ideal for the application of Phonon Glass Electron Crystal Concept. The cage like structure gives room to engineer its electrical and thermal properties without affecting the other. For the first time, CoSb3 stuffed with Yb and substituted with Te (YbyCoSb3-xTex) was synthesized by mechanical alloying and spark plasma sintering. The electrical and thermal properties were characterized for pure and doped material. A Seebeck coefficient value of ~ 160 μV/K was obtained at ~ 600-800 K for Yb0.075CoSb2.85Te0.15. The electric resistivity dropped from ~ 1000 μΩm for pure CoSb3 to ~ 9 μΩm for Yb0.075CoSb2.85Te0.15. Lattice thermal conductivity was significantly reduced to a very low value of 1.17 W/m.K by the addition of Yb atoms into CoSb2.85Te0.15 without significantly affecting its Seebeck coefficient and electrical resistivity. This value is comparable to those produced by the costly processing of nanostructured materials. A zT value of ~ 0.70 was obtained at 600 K. This research has shown that by engineering the defect chemistry of thermoelectric materials, it is possible to significantly reduce their thermal conductivity without compromising their electrical properties.

No description available.

To facilitate the long term osteointegration of Ti implants of various forms, methods aiming to facilitate hydroxyapatite deposition and enhance its adhesion to the Ti surfaces have to be developed. This work investigates the novel route of Ti surface functionalization with self-assembled monolayers (SAMs) in order to facilitate hydroxyapatite deposition and strengthen its bonding with the Ti surface and further equip the surface with localized antibiotic delivery to combat post-implantation infections. The main findings demonstrate that the formation of SAMs on non-model Ti substrates is challenging, since it requires the simultaneous control of many factors to achieve a densely packed well-organized SAM on a large surface area. By pre-treating the substrate with techniques such as electropolishing, the initial surface contamination can be kept at minimum while the hydroxylated surface remains smooth for the formation of well-oriented SAMs. Hence, after electropolishing, the Ti surface could be functionalized with molecules carrying reactive or neutral groups to facilitate hydroxyapatite deposition and/or antibiotic immobilization. Such a surface functionalization is found to facilitate hydroxyapatite deposition. The hydroxyapatite formed on SAM-modified Ti surfaces is made of small crystals of 6 nm and a 12 μm thick hydroxyapatite film, which can grow in 1 month. The SAM modified surfaces are covered with hydroxyapatite spheres in less than 7 days, while no spheres are observed on the unmodified Ti surface under similar conditions. Enhanced hydroxyapatite deposition rates on SAM-modified surfaces are explained by a decrease of nucleation barrier for hydroxyapatite. Additionally, preliminary investigations demonstrate the possibility of further functionalizing the Ti surface to allow the immobilization of antibiotic (Ciprofloxacin here) simultaneously with hydroxyapatite growth. The release of Ciprofloxacin was found to occur after 1 day and continue up to 20 days. The combination of these two functionalities on the Ti surfaces could find applications in load-bearing implants.

In recent years, there has been a considerable interest in organic semiconducting materials due to their potential to enable, amongst other things, low-cost flexible opto-electronic applications, such as large-area integrated circuitry boards, light-emitting diodes (OLEDs) and organic photovoltaics (OPVs). Promisingly, improved electronic performance and device structures have been realized with e.g. OLEDs entering the market and organic field-effect transistors (OFETs) reaching the performance of amorphous silicon devices; however, it would be too early to state that the field of organic semiconductors has witnessed the sought-after technological revolution. Initial progress in the field was mostly due to synthetic efforts in the form of enhanced regularity and purity of currently used materials, the creation of new molecular species, etc. In this thesis we show that the advancement of physico-chemical aspects – notably materials processing – and the realisation of increased order and control of the solid state structure is critical to realize the full intrinsic potential that organic semiconductors possess. We first investigated how the bulk charge-transport properties of the liquid-crystalline semiconductor poly(2,5-bis (3-dodecylthiophen-2-yl)thieno[3,2-b]thiophenes) (pBTTT-C12) can be enhanced by annealing in the mesophase. To this end, temperature treatment of a period of hours was necessary to realize good bulk charge transport in the out-of-plane directions. This behaviour is in strong contrast to in-plane charge transport as measured in thin-film field-effect structures, for which it was shown that annealing times of 10 min and less are often sufficient to enhance device performance. Our observation 4 may aid in future to optimize the use of pBTTT polymers in electronic devices, in which good bulk charge transport is required, such as OPVs. In the second part of thesis, we explored ink-jet printing of pBTTT-C12, in order to realize precise deposition of this material into pre-defined structures. In organic electronic applications this can, amongst other things, enable deposition of different semiconductors or reduction of the unwanted conduction pathways that often result in undesirable parasitic ‘cross-talk’, for instance, between pixels in display products. We demonstrate the integration of ink-jet printed transistors into unipolar digital logic gates that display the highest signal gain reported for unipolar-based logic gates. Finally, recognizing that a broad range of conjugated organic species fall in the category of “plastic crystals”, we explored the option to process this class of materials in the solid state. We find that solid-state compression moulding indeed can effectively be applied to a wide spectrum of organic small molecular and polymeric semiconductors without affecting adversely the intrinsic favourable electronic characteristics of these materials. To the contrary, we often observe significantly enhanced [bulk] charge transport and essentially identical field-effect transistor performance when compared with solution- or melt-processed equivalents. We thus illustrate that fabrication of functional organic structures does not necessitate the use of solution processing methods, which often require removal of 99 wt% or more of solvent, or precursor side-products, nor application of cumbersome vapour deposition technologies.

Protein adsorption under physiological conditions was recognised to be the key step in the modulation of biological responses between materials and an osseous environment. Many studies have shown variation of adsorption behaviour on medical materials but most experiments were performed under non-physiological idealised conditions with idealised samples. The aim of this thesis was to develop a method to analyse protein adsorption on real clinically relevant samples under physiologically relevant conditions. The use of fluorescent probes was identified as a methodology which would facilitate analysis under a range of conditions including fully competitive with real samples that required no specialised surface pre-treatment. Fluoresceinthiureidoaminocaproic acid (FTCA) and a sulforhodamine derivative (SR101), were identified as suitable for coupling to proteins. FTCA labelled bovine serum albumin (BSA) was initially used to validate the technique and found to have several advantages over commercially available total protein assays; including greater sensitivity and facilitate its use under competitive conditions. These experiments also confirmed sensitivity to temperature and test media as well as demonstrating that the technique could be used on idealised dense and real porous granular (as used clinically) samples. Conformational changes associated with protein-surface interactions were observed through variation in protein auto-fluorescence and confirmed with CD analysis, therefore, care in selection of appropriate experimental conditions and fluorophore probes was required. Additionally, labelling facilitated the visualisation in differences in the morphological habit of the surface adsorbed protein species. Investigation of differential response in protein exchange with hydroxyapatite (HA) and 0.8wt% silicon substituted hydroxyapatite (SA) with more biologically relevant proteins; such as bone morphogenetic protein-2 (BMP-2), fibronectin (FN) and osteopontin (OPN) individually and/or competitively in phosphate buffered saline (PBS) or minimum Eagles medium (MEM) supplemented with 10 % foetal bovine serum (FBS) demonstrated SA to have a greater capacity to adsorb selected osteogenic proteins under competitive conditions as compared to HA. Particularly interesting was the BMP-2 findings, which highlighted the role of media in promoting BMP-2 adsorption and the conformation sensitivity of traditional ELISA assays giving rise to unreliable results.

Biointerfaces bridge across inorganic and biological substances within a watercontaining environment. It is related to health care, environmental engineering and bioenergy generation. However, there is a lack of fundamental understanding of bonding and stability of biointerfaces, due to limited capabilities of experimental techniques. The research project employs molecular dynamics (MD) as the basic methodology to study selected biointerfaces, involving five carbon surfaces (amorphous carbon surface, basal graphite surface, basal graphite surface doped with hydrogen and hydroxyl groups, basal graphite surface with Stone-Wales defects, and edge graphite surface). The selected molecules are: a small alpha-helix and a beta-sheet peptide, each with 16 amino acids; and a mid-sized peptide (amyloid peptide). The systematic study of the molecular adsorption on carbon surfaces has shown that it is a very complex process, which depends on several factors such as the molecular structure, the hydropathy of the peptide molecule, the charge and defects of the substrate surface, and the orientation of the molecule upon adsorption. It is clear that the amino acids which face the surface initiate the adsorption process and influence subsequent stages of adsorption. The considered carbon surfaces have different levels of reactivity for the molecule adsorption. The amorphous and charged surfaces tend to stabilise the beta sheet secondary structure. The interaction between the amyloid peptide and the carbon surfaces seems to depend on its molecular orientation, as well as the nature of the carbon surface: it was clearly attracted to the hydrophobic basal surface of graphitic carbon but pushed away from the hydrophilic charge-doped surface in one of the orientations (the second), but the opposite is true for another orientation (the third). Details of the structural change were shown in the Ramachandran plot. The energy change of the system mainly comes from the configurational variation, and electrostatic interactions are more prominent than the others. Water molecules tend to accumulate above a hydrophobic surface, forming a dense water layer, with an estimated distance of 2.9 Å from the carbon surface, whereas they distribute relatively evenly on hydrophilic surfaces.

This thesis concerns the fabrication and modification of novel oxygen and glucose biosensors as well as the application of these biosensors in oxygen and glucose transport research in cell constructs. In Chapter 1, the principle and development of biosensors has been reviewed. Particular attention is paid to oxygen and glucose mass transport research in cell constructs which are crucial for bio-scaffold design in tissue engineering. Chapter 2 details the materials and methods in oxygen and glucose sensor fabrication, modification and characterization. Chapter 3 presents research into practical challenges in oxygen and glucose sensors. For oxygen sensor, membrane biofouling and sensitivity to stirring effect have been detected and successful progresses have been made to reduce their effects. For glucose sensor, membrane biofouling and oxygen tension reliance affect their performance. Remarkable contributions have been made to improve glucose sensors’ stability and reliability. In particular, micro-biosensors have been introduced in the interests of better sensor adaptability for further biomedical applications. Chapter 4 is the experimental section for biosensor applications, and thus provides a detailed description of the cell culture models used in the thesis. Chapter 5 describes the oxygen partial pressure and glucose concentration measurements using biosensors. 2D and 3D cell culture constructs are investigated and results are discussed in this section. It deserves to be mentioned that the modified oxygen and glucose sensor in this thesis are excellent for in vitro biomedical applications, the simultaneously investigation of PO2 and glucose concentration gradient in 3D cell constructs is also a pioneering work in this research field. Chapter 6 illustrates the overall conclusions resulting from the experiments described in the thesis and points out possible future research directions.

The increasing availability of nanopowders and nanotubes combined with new processing techniques is enabling the development of new multifunctional materials. Carbon Nanotubes (CNTs) are one of the recently discovered allotropic forms of carbon. They have exceptional mechanical, electrical and thermal properties. The application of CNTs in the reinforcement of ceramic nanocomposites has not yet been fully investigated and is the subject of this study. Alumina is the main matrix used in this study. CNTs need to be de-agglomerated and homogeneously distributed in ceramic nanocomposites. Dimethylformamide (DMF) produces fine and stable CNT and alumina dispersions. All nanocomposites were sintered by Spark Plasma Sintering (SPS). Nanocomposites prepared using DMF dispersions showed better dispersions, higher electrical conductivity and mechanical properties as compared to those prepared using ethanol dispersions. The addition of CNTs or Carbon Black (CB) to alumina significantly aids its densification. The CNTs produce significant grain growth retardation. CNTs were found to be well preserved in alumina after being SPSed up to 1900 oC. Structural preservation of CNTs in ceramic nanocomposites depends on the nature of ceramic and SPS processing conditions. The electrical conductivity of alumina – CNT nanocomposites is four times higher as compared to alumina – CB nanocomposites due to the fibrous nature and high aspect ratio of CNTs. Alumina coated CNTs were used for better interfacial adhesion with the matrix. Oxidative resistance of CNTs was increased by coating them with alumina and by decreasing the grain boundary area in alumina – CNT nanocomposites. Coated and uncoated CNTs showed higher mechanical reinforcement in alumina nanocomposite as compared to CB. The future for ceramic – CNT nanocomposites is very bright, especially for applications associated with the electrical and thermal properties. Apart from a good understanding of nanocomposites, the commercial development of CNT based technologies heavily relies on the availability and price of CNTs.

Ad hoc wireless networks have emerged as a promising communication scheme to meet the ever growing portability and infrastructureless demand of wireless services. The transmission power level affects signal quality and interference which causes congestion and thus impacts the communication performance. Hence, power control has been the focus of extensive research. In this thesis, we examine the problem of power control in wireless networks, specially in ad hoc wireless networks. Two important types of power control, which are power control with fixed SNIR targets and power control with variable SNIR targets, are discussed in the thesis. We first introduce some important techniques and results involved in the development of power control algorithms and give literature review. A PI power control approach from literature is introduced. Due to lack of stability analysis, we show there are problems in the existing algorithm. We then propose a stable Proportional-integral (PI) power control algorithm. A forgetting factor is adopted to improve the transient performance. Distributed power control algorithms for systems with fixed SNIR targets might diverge when the feasibility condition is not satisfied. Multi-objective optimisation (MO) is adopted to deal with power control with variable SNIR targets. After discussing the existing MO algorithm, we propose a quadratic multiobjective-optimisation (QMO) algorithm where a quadratic objective function and the greedy methodology are adopted for the dynamics. Theoretical and simulation results of convergence of the new algorithms are given. We also provide review of some important power control frameworks which can be used to show convergence of power control algorithms. However, the QMO algorithm does not fall into any existing framework. In order to show convergence of the QMO algorithm, we suggest a new generalised framework in this thesis.