Browsing by Author "Krynauw, Hugo"

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    Design and implementation of an apparatus for hydrodynamic and fatigue testing of prosthetic aortic valves
    (2008) Krynauw, Hugo; Marais, Stephan; John, Lester
    Aortic valve replacement in humans may be needed due to pathology leading to valve stenosis and regurgitation. Replacement is by either mechanical or soft tissue prosthetic valves. Before new valves are medically approved and introduced into the market they are required to undergo rigorous testing to verify performance and product life expectancy. Performance testing is done in a hydrodynamic test apparatus and life expectancy verified in an accelerated test apparatus. The Cardiology Department at Tygerberg Hospital has proposed a project for the design and implementation of a prosthetic aortic valve test apparatus. This device is to be used primarily for fatigue, but also limited hydrodynamic, testing of prosthetic heart valves. The design of the test apparatus was based on the four-element Windkessel model of the arterial system. This simple lumped parameter electrical analogy of the arterial system takes aortic and arterial resistance, arterial compliance, and blood inertance into account to simulate total arterial impedance. This model was developed with physiological reference and thus the element parameters only hold for physiological simulation as the equation governing impedance is speed sensitive. The model was adapted to provide theoretidal, physiological loads from physiological speeds of 60BPM through to accelerated speeds up to 1OOOBPM through mathematical optimisation of the Windkessel.The test apparatus was designed and built taking into account the varying Windkessel parameters where possible. Both compliance and resistance could be varied within an acceptable range, inertance however, could not be varied due to the limitations of the project. The apparatus was controlled and pressures on either side of the valve monitored with a LabView® graphical user interface. The apparatus was able to mimic in vivo closely and satisfied the ISO requirements for valve testing up to speeds of 230BPM. Various modifications are proposed to both the Windkessel model and the physical apparatus to compensate for hydrodynamic effects at high testing speeds in improve performance, as well as increase the maximum testing speed.
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    Optimization of structural and mechanical properties of electro-spun biodegradable scaffolds for vascular vissue regeneration
    (2013) Khatib, Rodaina Omar; Franz, Thomas; Krynauw, Hugo; Bezuidenhout, Deon
    Current replacements for diseased arteries include autologous and artificial grafts. The availability of autologous grafts is limited and artificial grafts tend to fail when applied to small calibre vessels (<;6 mm) due to graft thrombosis and mechanical mismatch between artery and graft. Tissue engineering offers a promising approach to overcome these shortcomings. With porosity as a fundamental prerequisite for tissue ingrowth, several techniques have been introduced for producing porous scaffolds including electro-spinning. This study involved the development and optimisation of electro-spun biodegradable scaffolds for vascular tissue regeneration by tailoring parameters of the electro-spinning process and investigating the change in mechanical and physical properties of the scaffolds associated with hydrolytic in vitro degradation.
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    Tailoring of the biomechanics of tissue-regenerative vascular scaffolds
    (2016) Krynauw, Hugo; Franz, Thomas; Bezuidenhout, Deon; De Beule, Matthieu
    The lack of long term patency of small diameter synthetic vascular grafts currently available on the market has directed research towards improving the performance of these grafts. Improved radial compliance matching and appropriate tissue ingrowth into the graft structure are main goals for an ideal vascular graft. In addition, the use of biodegradable materials offers the promising prospect of leaving behind a near native vessel with no synthetic material remaining. Tissue ingrowth into grafts alters their mechanics. This, combined with a loss of mechanical integrity over time, in the case of biodegradable scaffolds, brings the need to investigate how these changes play out and how to tailor them for optimal graft healing. This project set out to investigate the mechanics of electrospun Pellethane® 2363-80AE (Dow Chemicals) and DegraPol® (ab medica S.p.A) biostable DegraPol® DP0 and biodegradable DegraPol® DP30 scaffolds during in vivo animal studies. DegraPol® DP30 findings were used to investigate the scaffolds' potential use for vascular grafts by means of a finite element graft model. Porous, electrospun scaffolds were manufactured and implanted into two subcutaneous and one circulatory rat models. All studies consisted of four time points, namely 0, 7, 14 and 28 days. Scaffold morphology was characterised, and tissue ingrowth was quantified by histological analysis of explanted samples. Orthogonal, uni-axial tensile testing measured scaffold mechanical response of in-fibre and cross-fibre deformation. Tissue ingrowth brought about considerable changes in biostable DegraPol® DP0 scaffold mechanics. Tensile testing of degradable DegraPol® DP30 scaffolds in their load bearing circumferential direction showed a balance between a loss in mechanical strength and an increase in strength by tissue ingrowth. This resulted in constant radial compliance of 4.47 ± 0.14%/100 mmHg between 80 and 120 mmHg for the four week period predicted with the numerical models. The finite element model based on DegraPol® DP30 scaffold mechanics for 6 mm grafts showed better, i.e. higher, radial compliance than current grafts used clinically (polyethylene terephthalate and expanded polytetrafluoroethylene grafts). This stability in compliance, coupled with good tissue ingrowth is of scientific importance as it shows that highly aligned, porous electrospun DegraPol® DP30 scaffolds are a viable option for vascular grafting to achieve long term graft patency