published_or_final_version / abstract / Physiology / Master / Master of Philosophy

published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

published_or_final_version / Medicine / Master / Master of Medical Sciences

published_or_final_version / Nursing Studies / Master / Master of Nursing

Prosthetic cardiac valve surgery is a well-established technique, but the search continues for engineering materials with sup..e rior mechanical characteristics in order to extend the service life of the implant. The introduction of pyrolytic carbon was seen as a breakthrough in the development of wear resistant, non-thrombogenic materials for such applications. However, thrombo-embolic phenomena and the need for anticoagulation treatment following valve insertion remain the main problems associated with artificial materials in this application. The work carried out in this research has studied the haemocompatibility of a commercially available, wear resistant TiffiN/TiCfDLC multilayer structure, and a second TiN coating deposited by RF reactive sputtering of a titanium target in a ArIN2 environment, as candidate materials for a heart valve prosthesis. The structure of the RF deposited tiN coating was assessed as a function of deposition conditions, and was seen to develop a particular preferred crystallographic orientation. The nature of this texture was influenced by the condition of the underlying substrate. The effect of substrate condition on the biocompatibility of the tiN coating was studied by assessment of fibroblast attachment and spreading, and by haemolytic analysis of released haemoglobin. The results showed that the initial attachment and orientation of fibroblast cells was influenced by the substrate condition, but no influence on the degree of spreading and haemolytic nature was observed. Characterisation of the TiN coating and the components of the multilayer structure was carried out by Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), stylus profilometry and contact angle measurement. Haemocompatibility was studied by the interaction of the surfaces with plasma proteins, blood platelets and red blood ceUs. Cytotoxicity was studied using the MTT test. The degree of platelet activation on the surfaces correlated with their surface energy. The greatest degree of platelet spreading was observed on the more hydrophilic coatings. The lack of platelet activation seen on the DLC coating is attributed to its smooth surface and hydrophobic nature, resulting in higher levels of adsorption of anticoagulation proteins. The RF sputtered TiN coating caused significant levels of haemolysis and fibroblast cell death. None of the components of the multilayer structure caused such effects, although thrombus formation was observed to a degree on the Ti, TiN and TiC components of this structure. The toxic nature of the RF deposited TiN coating was not attributed to surface chemistry or roughness, but rather to a combination of the hydrophilic nature and the defect state of the surface.

Intracellular Ca2+ ions are highly regulated in animal cells for them to function normally. Since the tight regulation of [Ca2+]i is so ubiquitous among cells, it is not surprising that altered function in [Ca2+]i regulation is associated with a myriad of disease states in humans. This is particularly evident in pacing myocytes and nerve terminals related to synaptic transmission. A common thread through this dissertation is on the role of three regulators proteins that are common to many cell types. These are the plasmalemmal Na+/Ca2+ exchanger (NCX), the Ca2+-ATPase (PMCA) and the SERCA on the endoplasmic reticulum. In chapter 1 a historical overview is provided on how the understanding in the importance of Ca2+ came about. In Chapter 2, I address indirectly the function of residual [Ca2+]i on the efficacy of synaptic transmission by quantal analysis but also develop novel means of assessing quantal analysis to assign a n and p value to particular synapses. Chapters 3 and 4 address the role of the three Ca2+ regulator proteins in short bursts of synaptic transmission related to short-term facilitation or depression depending on the type of neuromuscular junction (NMJ). Two key model NMJs I used were the crayfish (Chapter 3) and the larval Drosophila (Chapter 4). For comparative purposes in investigating the role of the three proteins in [Ca2+]i regulation, I used the Drosophila larval heart preparation (Chapter 5). Throughout these studies, I used various pharmacological and ionic approaches to compromise the function of these Ca2+ channels. The results were unexpected in some cases due to non-specific effects of the pharmacological agent or ionic manipulations. In addition, a mutational line of Drosophila was used to asses SERCA function, but the results at the NMJ were not as expected. However, results with the mutation on the function of the heart were promising. The significance of these studies stresses that multiple approaches to compromise channels is warranted and the findings should be beneficial for future investigators to advance in mechanistic studies.

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