School of Chemistry - Theses
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ItemBiomaterial porous networks of hydroxyapatite and titanium dioxide( 2014)A gap in a bone that exceeds 2.5 times the bone radius is termed a critical size bone defect and will not heal naturally. The defect needs to be filled with a synthetic bone substitute (a biomaterial scaffold). \(\textit{In situ}\) delivery of medicinal drugs may assist with treating a bone defect, but current drug delivery vehicles (DDVs) are neither able to controllably release drug molecules nor allow for targeted delivery. Porous networks of either hydroxyapatite (HA) or anatase titanium dioxide could be used as biomaterial scaffolds or DDVs. Using sol-gel chemistry and a templating technique, the preparation of such networks, with potential as materials for biomedical applications, forms the research objective. Polyurethane sponge (PU), polyethylenimine-modified polyurethane sponge, polyurethane-agarose gel composite sponge (AG) and natural sea sponge were used as templates for open-celled, porous HA networks. Two concentrations of sol-gel precursor solutions were employed; the higher concentration obscured the template structure in the final network. The choice of template, multiple sol-gel coating, and the rate of temperature increase when removing the template by calcination led to evolution of the HA fibre surface. PU-templated and AG-templated HA networks were contrasted against each other, with the agarose gel component influencing results. All final networks were HA, but other calcium species were present as well. As an initial alternative to the HA networks, titanium dioxide networks were templated on PU sponge, but these lacked both high surface area and mesoporosity. Next, a Type I collagen gel was employed as a template for anatase titanium dioxide networks composed of mesoporous fibres. A standard method for titanium dioxide network preparation is firstly described, where selective solvothermal treatment preceded calcination. This is followed by modified preparations exploring the morphological transition from the collagen to titanium dioxide network structures, and solvothermal fluids containing varying solvent ratios or ammonia. The collagen fibres were 50-100 nm thick, while the titanium dioxide fibres had walls up to 300 nm thick but retained the collagen structure. Compared to networks that only underwent calcination, solvothermal treatment altered the fibre morphology and enhanced the textural properties (surface area, mesopore diameter and total pore volume). Three titanium dioxide networks, previously templated on collagen gel, and spanning a large surface area range were studied for possible biomedical applications. Biomineralisation took place in a simulated body fluid. Apatite grew on each network indicating in vitro bioactivity, but surface area may affect sustained biomineralisation. Ibuprofen drug delivery was monitored by two methods, with a loading of 58.9 mg/g achieved on the highest surface area network. The drug release was modelled as a sustained diffusion mechanism. Ibuprofen could be stored in mesopores or adsorb to the titanium dioxide fibre surface. Overall, HA and titanium dioxide porous networks were fabricated by sol-gel chemistry and templating. In general, morphology and textural properties were influenced by the choice of template, precursor concentrations and processing conditions, including the rate of heating, calcination time and solvothermal treatment. The collagen-templated titanium dioxide networks have potential as materials for biomedical applications.