Plasticised poly (vinyl) chloride (PPVC) is one of the most commonly utilised plastics in clinical practice. However, its has recently come under much scrutiny due to perceived adverse affects associated with migration of the plasticiser di (2-ethylhexyl) phthalate (DEHP) on contact of the PPVC with various biological solutions. This migratory behaviour, combined with DEHP being shown to be a toxin and an inflammatory mediator in animal and human models, has lead to further studies into its effects during extracorporeal interventions. In this thesis the migration and extraction of DEHP from PPVC was investigated using carbon-14 labelled DEHP. The study included the development of a biomaterial test cell for use in vitro and in a novel ex vivo rat perfusion model. In addition, the present study investigated DEHP migration in the clinical setting showing that plasticiser migration is a serious issue in pre-primed ECMO storage. We demonstrated the effectiveness of the radiolabel for migration studies, with DEHP concentration values that compared favourably with previous in vitro studies, also showing that the make up of the fluid exerts an influence on DEHP extraction with methanol (0.741±0.154mg/ml at 60 min; 2.21±0.02.16mg/ml at 300 min), blood (0.1067±0.0636mg/ml at 300 min) and plasma (0.0142±0.001652 mg/ml at 300 min) having differing values. The ex vivo studies showed that DEHP or its major metabolite MEHP is located in various tissues post procedure. The plasticiser tissue levels depended on the means of exposure, with gavage and perfusion models producing different deposition profiles that favoured the filtering and lipid rich organs respectively. Critically, the perfusion studies also revealed substantial DEHP levels in the brain. Although this thesis reports that carbon-14 is a suitable method of accurately detecting DEHP migration from PPVC, it is not the answer to this assay problem due to the logistical problems associated with radiation work. The ex vivo results also indicate the extrapolation of possible DEHP effects from perfusion interventions cannot be deduced from gavage studies due to the differences in deposition profiles.

Scale down models have been successfully developed and applied to the investigation of the effects of both dissolved oxygen and pH gradients, consequent of large scales of operation, on the biological performance of a culture of Bacillus subtilis. The strain used produces acetoin and butanediol as metabolites, and has been used as a model culture for mixing studies due to the unusual sensitivity of its product distribution to oxygen supply. It is a useful biological indicator of bioreactor performance. In addition, the sensitivity of metabolite production rates to pH has been exploited. Experiments using two different scale down models (two inter-connected stirred tanks and a stirred tank connected to a plug flow reactor) have been performed with the aim of simulating incomplete mixing with respect to oxygen supply. The effects of mean circulation time and the relative volumes of the compartments containing high and low dissolved oxygen concentrations, both in the ranges realistic of those found at large scales of operation, have been studied. For a given configuration, the biological response of the culture was consistent with the mixing conditions imposed. Similar trends (although significantly different in magnitude) in the biological performance of the culture in the two scale down models were found. Differences in performance between the two configurations have been explained in terms of the flow characteristics and oxygen availability in each system. The results presented also highlight the importance of the choice of the scale down model when studying the impact of large scale inhomogeneities on micro-organisms. The study shows that significant changes in biological performance are likely to occur upon scale up of this fermentation due to circulation of cells through oxygen deprived regions. These scale down experiments also indicate that both decreasing the mean circulation time and increasing the size of the well mixed impeller region should improve performance at the large scale. pH inhomogeneities can also occur in large scale fermenters near the addition point of acid or base for pH control as a consequence of poor bulk mixing. Frequent exposure of cells to such regions may affect microbial metabolism. Scale down experiments, under identical nonlimiting conditions of oxygen supply, have been used to simulate this phenomenon. It is shown that the effects of localised pH deviations from the bulk value on the biological performance of micro-organisms cannot be ignored for mixing times in bioreactors exceeding 60 seconds. Such effects of pH do not affect the growth of the culture. However, significant changes in product formation can be measured. Such scale down analysis may result in a better understanding of the effects of the physical environment on the biological performance of micro-organisms at different scales of operation, and help to produce a more rational approach to the design of bioreactors.

Phosphorylcholine (PC) based polymers have been used in medical devices to improve biocompatibility. In this study, PC based polymers were modified with either a cationic charge or combined with poly(butylmethacrylate) (PBMA) and their biocompatibility assessed through a series of biological assays. Protein adsorption assays revealed that the presence of a cationic charge significantly increased the number of proteins adsorbed. The total amount of protein adsorbed to PC with 30% cationic charge was considerably more then that adsorbed to the other samples. Fibronectin, albumin, complement factor B and immunoglobulins were found adsorbed to all samples. Clq however, was only adsorbed on samples containing 10% cationic charge or more. The presence of a cationic charge increased cell adhesion for both the fibroblast cells and the epithelial cells. Adhesion did not increase linearly with cationic charge, possibly due to alterations in protein adsorption, coating stability, and or cytotoxicity. Endothelial cells showed little to no cell adhesion on any of the PC cationic samples. Pre-coating materials in fibronectin increased endothelial cell adhesion, although this effect generally decreased as serum concentration increased. Pre-coating samples in laminin facilitated cell adhesion on PC with 20% cationic charge but not on PET or PC with 0% cationic charge. The combination of cationic charge and laminin may encourage cell adhesion, possibly through alterations in conformation of adsorbed proteins. Serum type affected adhesion and activation of mononuclear cells and granulocytes. The presence of a cationic charge increased the adhesion and activation of these two cell types. Adhesion and activation did not increase linearly with cationic charge, possibly due to differences in protein adsorption, coating stability and or cytotoxicity. The biocompatibility of PC and PBMA copolymer samples were assessed, looking at adhesion of corneal epithelial cells and macrophage cells. Adhesion of both of these cell these cell types increased as PBMA content increased and PC decreased. This is probably due to alterations in protein adsorption as a result of changes in surface hydrophobicity.

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