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Biofabrication has been receiving a great deal of attention in tissue engineering and regenerative medicine either by manual or automated processes. Different automated biofabrication techniques have been used to produce cell-laden alginate hydrogel structures, especially bioprinting approaches. , These approaches have been limited to 2D or simple 3D structures, however. In this thesis, a new extrusion-based bioprinting technique and a new simple, manual 3D biofabrication method are presented to culture cells in 3D. These methods do not rely on any complex fabrication methods. The bioprinting technique was developed to produce more complex alginate hydrogel structures. This was achieved by dividing the alginate hydrogel cross-linking process into 3 stages: primary calcium ion cross-linking for printability of the gel, secondary calcium cross-linking for rigidity of the alginate hydrogel immediately after printing and tertiary barium ion cross-linking for the long-term stability of the alginate hydrogel in the culture medium. Simple 3D structures including tubes were first printed to ensure the feasibility of the bioprinting technique. Complex 3D structures, such as branched vascular structures, were subsequently printed successfully. The static stiffness of the alginate hydrogel after printing was 20.18 ± 1.62 kPa which was rigid enough to sustain the integrity of the complex 3D alginate hydrogel structure during the printing. The addition of 60 mM barium chloride was found to significantly extend the stability of the cross-linked alginate hydrogel from 3 days to beyond 11 days without compromising the cellular viability. The results based on cell bioprinting suggested that the viability of U87-MG cells was 92.94 ± 0.91 % immediately after bioprinting. Cell viability was maintained above 88 ± 4.3 % in the alginate hydrogel over a period of 11 days. On the other hand, the manual biofabrication approach developed in this thesis enabled the fabrication of scalable 3D cell-laden hydrogel structures easily, without complex machinery. The technique could be carried out using only apparatus available in a typical cell biology laboratory. The fabrication method would involve micro coating cell-laden hydrogels covering the surface of a metal bar by dipping into cross-linking reagent CaCl2 or BaCl2, to form hollow tubular structures. This method could be used to form single- or multi-layered tubular structures. This fabrication method has incorporated the use alginate hydrogel as the primary biomaterial and secondary biomaterial could be added depending on the desired application. The feasibility of this method has been demonstrated by showing the cell survival rate and normal responsiveness of cells within these tubular structures using mouse dermal embryonic fibroblast cells and human embryonic kidney 293 cells containing a tetracycline responsive red fluorescence protein (tHEK cells). By adjusting the fabrication protocol, complex hollow alginate hydrogel structures could be generated.

The term Nanoceramics is well known in the ceramic field for at least two decades. In this project a detailed study was performed on the synthesis of α-alumina nanopowders. High solids content nanoalumina suspensions were prepared and used to form green bodies using both wet and dry forming routes. The green bodies were then sintered using both conventional single and two-step sintering approaches. Synthesis: Two different synthesis methods, viz. precipitation and hydrothermal treatment, were used to synthesize fine α-alumina powders from aluminium chloride, ammonia solution and TEAH (Tetraethyl ammonium hydroxide). XRD, TEM and FEG-SEM were used to characterise the powders produced. The presence of commercial α-alumina powder as seed particles did not affect the transformation to α-alumina phase during the hydrothermal treatment at 220˚C in either basic or acidic environments. The results obtained from the precipitation route showed that the combined effect of adding α-alumina seeds and surfactants to the precursor solution could lower the transformation temperature of α-alumina from about 1200˚C for unseeded samples to 800˚C, as well as reducing the level of agglomeration in the alumina powders. The difference in transformation temperature mainly resulted from the nucleation process by the α-alumina seeds, which enhanced the θ → α transformation kinetics. The lower level of agglomeration present in the final powders could be due to the surface modifying role of the surfactants preventing the particles from growing together during the synthesis process. By introducing a further high-temperature step for a very short duration (1 minute) to the low-temperature heat treatment route (800˚C/12 h), the unseeded sample with added surfactant transformed into pure α-alumina phase. The newly-added step was shown to be an in-situ seeding step, followed by a conventional nucleation and growth process. The best final powder was compared with a commercial α-alumina nanopowder. Processing of alumina ceramics: The effect of low-molecular weight ammonium dispersants including Dispex-A40, Darvan-C and Dolapix-CE64, on high solids content nanoalumina suspensions was investigated. The nanosuspension prepared using the most suitable dispersant, Dolapix-CE64, was slip cast into ~53% dense, very homogeneous green bodies. This nanosuspension was also spray freeze dried into crushable granules using Freon as a foaming agent. Green compacts with density of ~53.5% were then formed by dry pressing the 2 vol% Freon-added spray freeze dried granules at 40 MPa. Both slip cast and die pressed green bodies were sintered using conventional single-step and two-step routes followed by characterising the density and grain size measurement of final dense compacts. The results have been compared with that of a submicron alumina ceramic prepared using a commercial α-alumina suspension. Highly dense alumina with an average grain size of ~0.6 μm was fabricated by means of spark plasma sintering at 1200˚C. The application of 500 MPa allowed achieving almost fully dense alumina at temperature as low as 1200˚C for 30 minutes with no significant grain growth.