Thesis (doctoral)--Ludwig Maximilians-Universität zu München, 1979.

Thesis (MScEng)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

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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.

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Valvular heart disease (VHD) continues to have significant effects on many people’s lives, with numbers expected to grow tremendously over the next few years. Individuals suffering from severe valvular heart disease usually require a heart valve transplant in order to restore the native valve’s vital unidirectional flow regulation. Therefore, artificial heart valve (AHV) research is of very high importance. Previous research studies have provided substantial input in the realm of AHV design relative to durability, thrombotic and hemolytic potential, and overall functionality. However, modifications continue to be warranted due to limitations in the accuracy and time efficiency of the in vitro physiological flow replication process. The objective of this investigation is to develop and analyze a method of AHV performance evaluation using a novel test chamber within an automated mock circulatory loop. The constructed mock loop was designed to maintain consistency of current industrial and academic research systems while providing innovative loop component control that allows for run-time changes and performance screening to various physiological conditions. Pressure sensors, ultrasonic flow meter, process controls and mechanical feedback sensors are managed via Labview in order to provide sufficient real-time performance analysis during system operation. In addition, a unique mechanical heart valve (MHV) test chamber was constructed to incorporate the test AHV in the mock loop flow path. This research exposes a test tilting disk MHV to a series of 12 heart rate and stroke volume combinations so as to evaluate the system’s effectiveness in pathological condition replication with respect to AHV design research. A Particle Image Velocimetry (PIV) system was utilized to illuminate particles in the flow field and obtain representative vector plots. Results of this study validate the combined experimental test chamber and automated mock circulatory loop as a viable MHV performance evaluation system by using real-time pressure and flow data to analyze system fluid dynamics at the MHV test site. Consequently, the use of this arrangement in MHV performance analysis greatly improves upon time restraints and accuracy concerns associated with currently used manually controlled setups.

Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Haj-Ali, Rami; Committee Member: White, Donald; Committee Member: Will, Kenneth; Committee Member: Yavari, Arash; Committee Member: Yoganathan, Ajit. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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