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Hepatocytes are the main functional cells of the liver and are used extensively in vitro for predicting in vivo drug toxicity profiles. However, the predictive accuracy of in vitro hepatocyte models depends on the physiological relevance of the artificial growth environment. Conventional in vitro hepatocyte models have employed monolayer cultures on two-dimensional (2D) substrates, forcing cells into a flattened morphology that is far removed from the in vivo scenario. Unsurprisingly, 2D cultures often show significant deviations from native liver genotype and phenotype and so are unable to accurately predict drug toxicity. Accordingly, it is hypothesised that approximating the native liver three-dimensional (3D) tissue architecture in vitro will help to preserve genotype and phenotype and so improve predictive accuracy. In this study, emulsion templated porous polymers were investigated as scaffolds for 3D hepatocyte culture. In particular, porous polystyrene scaffolds were explored due to their high porosity, reproducibility and suitable mechanical strength properties. Hepatocytes were cultured on polystyrene scaffolds under a range of culture conditions and were found to approximate native liver density and architecture. The morphology of hepatocytes in scaffolds was representative of in vivo, unlike the flattened morphology of 2D cultures. Crucial ultrastructural features involved in drug detoxification such as bile canaliculi were also present in scaffold cultures, but almost absent from 2D cultures. Importantly, these representative structural features translated into functional and genetic improvements in vitro. Hepatocytes in scaffolds displayed increased albumin synthesis, a key marker of hepatocyte function. Hepatic cell lines also showed increased resistance to drug toxicity compared to 2D cultures. Hepatic drug metabolising genotype was also increased to more physiologically relevant levels in scaffolds compared to 2D cultures. In addition, emulsion templated polystyrene scaffolds were also made more biochemically relevant by surface functionalising with galactose, a ligand known to selectively bind to hepatocytes in vivo via the asialoglycoprotein receptor (ASGP-R). Scaffold morphology was maintained with the incorporation of galactose, allowing cells to approximate native liver tissue architecture. Moreover, the pendent galactose ligands were found to be accessible to hepatocytes adhering onto the scaffold. In summary, this thesis has shown that emulsion templated porous polymers can offer a more physiologically relevant growth environment for hepatocytes in vitro. This could have a profound effect on improving drug toxicity predictions and so reducing the dependence on animal testing.

The purpose of this thesis is to investigate associations between parasite infection and host life-history variation in the wild Soay sheep population of the islands of St Kilda, NW Scotland. Studying host-parasite interactions in wild animal populations is of interest because of the importance of heterogeneity in resource availability, genetics, and environmental conditions in determining resistance to parasites, with implications for human populations and wildlife conservation and management. However, very few studies are able to investigate these associations in a longitudinal manner, which is essential in order to understand how infection is associated with life-history variation across ages and environmental conditions. In this thesis, I investigate associations between parasite resistance and ageing and the importance of maternal effects on offspring parasite resistance. I also establish the shape of natural selection on parasite resistance, and associations between measures of parasite burden and antibody responses. The principle findings of the analyses presented in this thesis are: i) Adult sheep of both sexes show a decline in parasite resistance in old age which is consistent with senescence. Furthermore, the rate of decline in parasite resistance with age is accelerated in individuals that have experienced more stressful environmental conditions over their lifespan. ii) Aspects of maternal phenotype and lamb early life performance are significantly associated with parasite resistance in lambs. Some of these effects persist into adult life and may even affect late-life changes in parasite resistance with age. iii) Analysis of ageing in five female reproductive traits shows that the contributions of individual senescence, terminal effects, and selective disappearance vary across traits, and that therefore multiple traits should be studied in order to understand ageing more fully. Most strikingly, there was no evidence for significant senescence in the probability of producing twins. iv) The first estimate of the strength of natural selection on parasite resistance in a longitudinally-monitored population provided evidence for positive selection on parasite resistance in lambs but not adults. Selection in lambs also varied across environmental conditions, being stronger in years of more favourable conditions. v) Analysis of associations between estimates of parasite burden and antibody responses showed that an estimate of parasite burden was not correlated with either a general or parasite-specific antibody response. However, antibody responses were positively correlated, and there was some evidence for a genetic correlation between the two in lambs but not adults.