Microextrusion freeforming of ceramic lattices from high solids ceramic pastes is a method for forming complex multi-scale hierarchical porous structures. It has the advantages of low shrinkage stress, high sintered density and environmental compatibility. A user friendly graphical user interface (GUI) was created so that the micro-extrusion freeforming worktable could be made very easy to manipulate even for a beginner. A solvent-based approach to paste preparation for extrusion freeforming was established, involving selection of solvent, polymer and dispersant. The parameters in the process such as solid fraction in the paste, paste viscosity, extrusion rate, X, Y table velocity, filament diameter and the volatilization of the solvent were studied. A substrate material which provided sufficient adhesion to resist shrinkage efficiently and also allowed the extruded lattice to be easily detachable was selected. The extrusion pressure in the alumina paste was monitored and was found to be useful in predicting and optimizing the extrusion behaviour. Hydroxyapatite (HA)/ tricalcium phosphateTCP and alumina lattices were directly fabricated using 80-500 μm diameter filaments. This thesis reports the implementation of design and fabrication of these scaffolds for tissue engineering, band gap materials and micro-fluidic devices. Multi-scale hierarchical void structures were fabricated and tested in vivo for regenerative medical applications. A co-extrusion nozzle assemble was design to produce tubular alumina lattice.

Soft tissue breakdown occurs in association with biochemical changes that can be attributed to a reduction in blood and lymph flow to a localised tissue area in response to applied pressure. The resulting ischaemia can lead to a reduction in available oxygen and accumulation of waste products. Tissue breakdown leading to the development of pressure sores afflicts patients who are already debilitated, although not all patients appear to be equally susceptible. Measurement of sweat biochemistry and blood gas tensions may reflect the biochemical process in the underlying tissues and provide a simple and non-invasive method of investigating the status of soft tissues. The potential of specific sweat metabolites to act as markers of soft tissue status during and following loading has been investigated at a clinically relevant site in healthy volunteers, and in two clinically relevant patient groups. A range of validation procedures were undertaken and a series of parameters derived to investigate the temporal profile of sweat biochemistry, and identify various modes of gas tension response. Investigations at the loaded sacrum of healthy individuals showed a statistically significant increase in sweat lactate, urea, urate and chloride concentrations which were dependent upon the level of externally applied pressure. Mean increases of between 10%-60% were demonstrated for sweat metabolite concentrations at the loaded site compared to the control site for applied pressures in the range 40-120 mmHg. Similar increases were demonstrated in sweat collected from highly loaded tissue areas within the stump socket of lower limb amputees. A threshold value for P02 tension was identified, amounting to a 60% reduction from the unloaded value, which was associated with elevated tissue carbon dioxide levels as well as increased sweat metabolite concentrations in the loaded phase. This finding may provide a useful predictor of soft tissue status during prolonged loading. No pessimist ever discovered the secrets of the stars, or sailed to an uncharted land, or opened a new heaven to the human spirit. Helen Adams

The room temperature polymerising heterocyclic polymer system, poly(ethyl methacrylate)/tetrahydrofurfuryl methacrylate (PEM/THFM) has been shown previously to be biocompatible and supported tissue repair, specifically for bone and cartilage, and biologically inert when in contact with the dental pulp. It proved more effective, than other glassy methacrylates in the release of active species. The PEM/THFM system is a rigid material. The aim of this study was to develop and characterise the use of this system as a flexible patch, for application and retention to the buccal mucosa, thus facilitating sustained regulated release. Model species, dextrans, were used to represent macromolecular drugs whereby the effect of molecular weight could be studied. N-methyl pyrrolidone was added to the polymer system as a biocompatible plasticiser to enhance molecular mobility, and hence the transport of species. The effect of the addition of chitosan was also studied, due to its bioadhesiveness and permeation enhancing ability. A range of systems was investigated both in terms of water and species release. The release of the agent was measured by a fluorometer, the leachable components by HPLC and Confocal microscopy demonstrated the transport of water and active species through the system. Immunological and viability studies established whether the leachants or released components of the polymeric systems had an inflammatory or irritant action on `in vitro' stratified epithelium. The addition of N-methyl pyrrolidone, dextran and chitosan substantially increased water uptake, thus affecting the release kinetics. Analysis of the kinetics of water uptake showed Case I, combination of Case I and Case II, and Case II kinetics, depending on the systems studied. Dextran release was largely diffusion controlled, from which diffusion coefficients were calculated; the amount released varied between the systems studied.

A variety natural materials that are environmentally friendly, renewable and low cost have been created. Bacterial cellulose (BC), which is produced by a harmless bacterium, Acetobacter xylinum, has been used as a reinforcement agent to form bionanocomposites. Apple and radish pulp which are themselves cellulosic, were blended with bacterial cellulose to produce a high quality nanopaper which can be used for special purposes. The resulting sheets are characterised in terms of their morphology as well as their mechanical and thermal properties. Another approach adopted was the combination of BC with bio-polymers such as poly (ε-caprolactone) and a commercially available starch based polymer, Mater-Bi. Freeze-dried BC, which was kept in its 3D shape, was used as a comparison. These innovative composite systems are non-petroleum based and are biodegradable. The morphology, structure, thermal properties and performance of the resulting bio-composites were investigated using scanning electron microscopy, Fourier Transform Infrared spectroscopy, Differential Scanning Calorimetry, Dynamic Mechanical Analysis, and by measuring the mechanical properties. Purification is a crucial step in removing impurities and another organic materials remaining in the BC. The BC gel which was purified in two steps, i.e. with 2.5 wt.% NaOH and then bleaching with 2.5 wt.% NaOCl respectively, showed a greater performance in its thermal and mechanical properties. In addition, it was shown that the cellulose I structure of BC is not converted to cellulose II. BC is an interesting material for in-vivo studies. However, to make it an interesting biological composite a suitable resin must be found. Poly (vinyl alcohol) (PVA) is a known water soluble polymer and is therefore a suitable candidate material. In this study BC was grown in PVA solution to produce an in-situ composite. The concluding work for this project is an in-vitro study of BC for scaffolds for tissue engineering. The BC network was seeded with bovine chondrocytes (bone cells) obtained from an 18 months old deer and cultured into the BC gel to establish the viability of this material for medical applications.

Natural rubber (NR)/organoclay nanocomposites were prepared using organomontmorillonite (OMMT) and organo-sepiolite (OSEP). Both were found to improve modulus significantly more than equivalent amounts of conventional fillers such as carbon black for strains up to 100%. OSEP was found to increase modulus more than OMMT for a given filler content, and NR/OSEP nanocomposites also had potentially anisotropic physical properties. OMMT had more effect on vulcanisation than OSEP, although both produced considerable acceleration. The tensile stress-strain behaviour of NR/OMMT and NR/OSEP nanocomposites were studied using a number of different micromechanical models. Some models were found to give a good empirical fit with experimental data, with the best results given by the Halpin-Tsai model. Furthermore, by analysis of the vulcanisation behaviour using rheometry, and particle morphology using transmission electron microscopy (TEM), it was possible to accurately estimate the Young's modulus of a nanocomposite from knowledge of the cure onset time and the shape factor of the particles. It was discovered that unmodified montmorillonite and sepiolite clays could undergo organic modi cation in situ during mixing into NR following the addition of a suitable modifier. This resulted in vulcanisates with very similar physical properties to those found when using pre-modified OMMT or OSEP. TEM and X-ray diffraction showed that the exfoliation state of the clay modified in situ was also similar to that of pre-modified organoclay. Silane coupling agents were also used with NR/OMMT and NR/OSEP nanocomposites, producing significant increases in modulus. However, the increased modulus was only observed above 40% strain for OMMT and above 25% for OSEP. The coupling agents strengthens the rubber- ller interface preventing interfacial slippage and cavitation in the nanocomposite, and these mechanisms only begin to operate when the interfacial stress reaches a significant level. The most effective coupling agent used was bis[triethoxysilylpropyl] tetrasulfide due to its relatively high reactivity.

Ceramic injection moulding is already established as a production technique for complex shaped ceramic components. However the process is limited to thin section mouldings generally not exceeding a wall thickness of 10 mm. The global objective of this work is to describe and understand the aetiology of defects which preferentially appear in thick injection moulded ceramics, and to find ways to overcome these problems. The following stages are examined mould-filling, solidification, binder removal and sintering. Different moulding techniques; conventional moulding, modulated pressure moulding, insulated sprue moulding and low hold pressure moulding were applied. Moulding thicknessw as systematicallyv aried (15,20,25, and 35 mm).. Hold pressures and times were closely controlled and found to be decisive processing parameters for defect creation. The use of insulated sprue moulding prevented void formation in 25 nun thick mouldings and the application of low and constant hold pressures (>5 MPa) led to a reduction of residuals tressesin the mouldings. An intensive study was carried out on the binder removal stage in which the catalytic removal of the polyacetal binder enabled removal of the binder from sections of 35 nun thickness. The reaction and transport kinetics during binder removal were studied and close observations were made out on various defects which could appear during interrupted binder removal. Differential shrinkage of the ceramic components during sintering was studied and could be tracked back to flow-induced particle alignment during mould filling. The sintering behaviour of the alumina feedstock used in this study was compared with an equiaxed zirconia powder injection moulding suspension. The phenomenon of jetting in large section mouldings and the creation of spherulites during solidification of the polymer were found to influence moulding structure.

The thesis presents a wide range of studies on carbon black and silica particulate reinforced rubbers. These include stress-strain, strain energy function, static and cyclic stress relaxation (stress softening), trouser test piece tearing and cyclic crack growth studies. The novel features of the work include the development of a simple strain energy function which is shown to represent the stress-strain behaviour of carbon black and silica filled rubbers up to strains of 100%. The numerical values of the constants in this function are shown to vary in a meaningful and systematic manner with the fraction of reinforcing filler and with the crosslink density. The cyclic stress relaxation studies are the first of their kind and demonstrate a significantly increased relaxation rate resulting from cycling in filled rubbers. The trouser tearing studies give some insight as to the materials and experimental variables that determine the type of tear growth and regime of tearing. The process of stress whitening around the tear tip during steady tearing in silica filled compounds provide the first opportunity to quantitatively relate the tearing energy to the hysteresis energy loss in a known volume of rubber at the tear tip. The cyclic crack growth studies show for the first time a systematic decrease in crack growth per cycle (dc/dn) at a given tearing energy as the carbon black filler content is systematically increased and as the crosslink density is decreased. A novel feature of the work is the demonstration of the effect of pre-strain in one direction on the cyclic growth rate of a crack in this direction when cyclically strained in a direction at right angles. The very large increase in dc/dn with increasing pre-strain is discussed in terms of pre-orientation of the rubber/carbon black structure.

Accidents, surgery and disease often result in the use of biomimetic materials that can replace human hard tissue and calcium phosphate bioceramics are ideally suited for this purpose. Indeed, biological apatite is a poorly crystalline, non-stoichiometric carbonated hydroxyapatite. The composition, crystallinity and particle size of synthetic calcium phosphate bioceramics directly affect their biological, mechanical and thermal performance. Hence control over these properties in synthetic bioceramics is essential in order to mimic human hard tissue in functionality. The existing methods of synthesis of calcium phosphate bioceramics are multi-step, time consuming and require strict control over synthesis conditions. Therefore, there is a requirement of a one-step, rapid synthesis technology which allows control over particle properties. The continuous hydrothermal flow synthesis (CHFS) technique addresses all such issues but it has not been used to synthesise calcium phosphate based nano-bioceramics. The work in this thesis involves the use of CHFS technology to synthesise calcium phosphate bioceramics. It was demonstrated that the rapid crystallising environment in a CHFS system resulted in phase-pure crystalline hydroxyapatite (HA). Traditionally required long ageing times and heat-treatment were avoided. Furthermore, variations in the CHFS system parameters were correlated with properties of the synthesised nanobioceramics. The CHFS system was also used to substitute biologically beneficial ions (C03'-, Si044-, Mg2+ and Zn2) into HA. Some ionic substitutions affected thermal stability and phase composition. For example, increase in magnesium contents in solution resulted in precipitation of a phase pure Mg-Whitlockite phase. Conventional consolidation methods of HA powders require several hours of exposure to elevated temperatures which results in large grains, phase decomposition and poor mechanical properties. Spark Plasma Sintering on the other hand is capable of very high heating and cooling rates. Phase-pure and ion-substituted calcium phosphates and zirconia-hydroxyapatite phase mixtures were spark plasma sintered to high densities with these materials displaying good mechanical properties.

The main objective of this research is to understand the mechanisms of interlaminar toughness using non-woven veils as the interleaf materials. The vacuum assisted resin transfer moulding (VaRTM) method was chosen for making specimens. Several types of non-woven veils were used as the toughening materials, because the non-woven veil was expected for good resin permeability. Three types of carbon fabrics, (plain, 5-harness satin, and unidirectional) and two types of resins (epoxy and vinyl ester) were selected for base materials. Firstly, the Mode-I and Mode-II interlaminar toughness tests, which are double cantilever beam (DCB) and four-point end notched flexure (4ENF) tests, were carried out to evaluate the effect of toughening by the interleaf veils. The mechanisms of the improvement by the interleaf veils were evaluated by microscopy. The adhesion between veil fibres and matrix is an important factor of the improvement of the interlaminar toughness. If veil fibres have poor adhesion to resin, these fibres would be pulled out from the matrix and work as fibre-bridging. In contrast, good adhesion of veil fibres is not necessary improvement of the interlaminar fracture toughness. Because these fibres are embedded in the matrix and interleaf veil cannot contribute to suppression of the crack propagation. The second stage of experiments was impact and compression after impact (CAI) tests. In this stage, the base materials were plain weave fabric only. Impact damage was evaluated using ultrasonic C-scan. The polyamide veils interleaved samples had superior impact and CAI resistance properties in all interleaved materials. In the final stage, correlation between each mechanical property was analysed and discussed. It was found that the relationship between each fracture toughness is affected by fabric and resin. Moreover, this work and previous literature data were compared. It can be found that the non-woven veils are effective toughening materials.

Polymer coatings are widely used in many industrial applications such as coatings on car bodies and refrigerators, and as varnishes on floor coverings and wood. As protective coverings polymer coatings are subject to wear and degradation making their mechanical properties a key performance indicator. Mechanical properties of non-polymeric coatings can be successfully determined using nanoindentation. However, the time-dependent nature of the mechanical properties of polymers requires a different approach to that used for time-independent materials. Spherical nanoindentation using a ramp and hold load method and creep analysis was compared to tensile testing and has produced results that fully characterise the timedependent mechanical response. Using this method differences in mechanical properties between different polymers as well as the changes in mechanical properties due to degradation and aging were distinguished. In conventional instrumented indentation tests contact areas are calculated from the measured depth based on Hertzian contact mechanics. Finite element analysis has suggested that spherical indentation is indeed Hertzian for visco-elastic materials. Direct observations of the contact area of visco-elastic materials under load were made simultaneously with depth measurements by indenting transparent polymers at a macro-scale. This novel approach suggested that for some polymers spherical indentation can be non-Hertzian. It appears that the ramp load times as well as surface properties contribute to the non-Hertzian contact. Consequently, moduli obtained from nanoindentation tests may not always be directly comparable to moduli obtained from tensile tests. These results will support the development of standard nanoindentation test procedures for visco-elastic polymers.