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Ozongeneratorer ¨ar v¨aldigt anv¨andbara vid reng¨oring och kan appliceras p˚a en m¨angd olika s¨att, bland annat rening av vatten. F¨oretaget Primozone utvecklar konkurrenskraftiga ozongeneratorer. Vid de system d¨ar ozonet tills¨atts direkt i vattnet kan ett bak˚atfl¨ode ske vid maskinfel. Generatorn ¨ ar mycket k¨anslig f¨or vatten och d¨armed beh¨ovs ett skyddande system. Primozone anv¨ander en mekatronisk skyddsventil f¨or att hindra eventuellt bak˚atfl¨odande vatten. I arbetet utvecklas en ny version av skyddsventilen ˚at Primozone d¨ar m˚alet ¨ar att reducera brister och ¨oka prestandan. Projektet resulterar i tv˚a skyddsventiler. En ren optimering av den nuvarande skyddsventilen ang˚aende bland annat pris, estetik, tillverkning, inkapsling och vikt- och materialminsking med samma prestanda. Den andra skyddsventilen erbjuder stora prestanda¨okningar och ¨ar f¨ordelaktig vid st¨orre system d¨ar annars flera skyddsventiler hade beh¨ovts anv¨andas. / Ozone generators are very useful in sanitation and can be applied in a variety of ways, including water purification. The company Primozone develops competitive ozone generators. In the systems where the ozone is added directly into the water, a backflow can occur in the event of machine failure. The generator is sensitive to water and therefore a protective system is required. Primozone uses a mechatronic protection valve to prevent any backflowing water. During this project a new version of the protection valve for Primozone is developed, where the goal is to reduce shortcomings and increase performance. The project resulted in two protective valves. One pure optimization of the current protection valve including price, aesthetics, weight, manufacturing ,encapsulation and material reduction with the same performance. The second protection valve offers high performance gains and is advantageous in larger systems where otherwise several safety valves would have been needed.

Graphene is a 2D material well known for its high intrinsic strength of 100 GPa and Young’s modulus of 1 TPa. Because of its 2D nature, the most promising avenues to utilize graphene as a mechanical material include incorporating it as reinforcement in a nanocomposite and creating free-standing foams and aerogels. However, the current techniques are not well-controlled – the reinforcing graphene particles are often discontinuous and randomly dispersed – making it difficult to accurately model and predict the resulting material properties. Here we aim to develop a framework for a new class of nanocomposites reinforced not by discrete nanoparticles, but by a continuous 3D graphene network. These 3D graphene networks were formed by chemical vapor deposition of graphene on periodic metallic microlattices, thereby providing mechanical reinforcement for the lattices. To assist in the lattice design, analytical models were derived for the mechanical properties of core/shell composite lattices and experimentally validated through compression testing of polymer lattices coated with electroless Ni-P. The models and experiments showed good agreement at lower shell thicknesses, while there was divergence at higher thicknesses, likely due to fabrication imperfections. The analytical models were also applied to hollow metallic lattices coated with graphene and compared to experimental data. The results showed that the models are plausible and suggest that graphene has a significant strengthening effect on the microlattices. These studies represent a paradigm shift in the design and fabrication of nanocomposites as one may now precisely prescribe the placement of the reinforcing nanomaterials. On a broader scale, this work also lays the framework for using a 2D material to span 3D space, enabling further exploration of 2D material properties and applications. One potential application area for a graphene-reinforced polymer composite is in prosthetic heart valves. The tissue of a human heart valve leaflet is heavily reinforced with networks of collagen and elastin fibers. One could similarly incorporate a graphene network as reinforcement within the polymeric leaflets of a prosthetic valve. One promising application of polymeric valves is in growth-accommodating implants for pediatric patients. Here we aim to develop a polymeric valved conduit that can be expanded by transcatheter balloon dilation to match a child’s growth. We designed the valve, characterized and selected materials, fabricated the devices and performed benchtop in vitro testing. The first generation of an expandable biostable valved conduit displayed excellent hydrodynamic performance before and after permanent balloon dilation from 22 to 25 mm. The second generation has shown the potential for a greater dilation from 12 to 24 mm. These results demonstrate concept feasibility and motivate further development of a polymeric balloon-expandable device to replace valves in children and avoid reoperations.

Mitral valve prolapse (MVP) is thought to be one of the causes of unexplained cardiac arrest (UCA). However, previous studies are limited by the lack of a standardized evaluation of UCA and the absence of a control group to identify predictors of cardiac arrest. We performed a systematic review of studies that examined the yield UCA evaluation. We then reported the prevalence and characteristics of MVP patients from a multi-centre registry of patients with UCA. Lastly, we completed a protocol of a matched case-control study aiming at comparing echocardiographic features of MVP patients with and without cardiac arrest. As a result of these studies, we proposed a standardized algorithm for UCA evaluation and a definition for idiopathic ventricular fibrillation. Also, we reported the prevalence of MVP in patients with UCA and described few features that could potentially help distinguish patients with MVP at risk for cardiac arrest.

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<p> A stress analysis of porcine aortic valve leaflets in diastole at 80 mm. Hg. in-vitro is presented. Incorporations of local surface geometry, leaflet material inhomogeneity, anisotropy and non-linearity are applied. The stress theory used is a modified form of the thin membrane stress theory for a homogeneous, linearly elastic and orthotropic lamina. Modifications are made so that the linear Hooke's Law equations of stress may be applied to the inhomogeneous, non-linearly elastic and orthotropic thin membrane aortic valve leaflets. </p> <p> Stress calculations are made on the premise that the diastolic valve leaflets at 80 mm. Hg. are in pre-transition (that is, characterized by a small elastic modulus) for the circumferential direction, and in post-transition (that is, characterized by a large elastic modulus) for the radial direction. Circumferential stresses are calculated to be relatively negligible; they are estimated to be less than 1 gm/mm². Radial stresses for the non coronary leaflet lie primarily in the 0 to 20 gm/mm² range. The regions of the largest stress concentrations are in the areas of mutual leaflet coaptation, especially near the Nodes of Aranti. A progressive increase of the radial stresses from the sinus annulus edges toward the coaptation edges of the leaflets is also observed. Based on the one valve reported , it appears that the left coronary leaflet is the highest stressed and the right coronary leaflet is the least stressed. Central leaflet radial stresses for the right coronary leaflet are in the 0 to 10 gm/mm² range, as compared to 0 to 20 gm/mm² for the non coronary and left coronary leaflets. </p> <p> The question as to whether the diastolic strains of the valve leaflets are in pre-transition, transition or post-transition is raised. The resolution of the question is seen to be critical to the validity of the stress analysis. It is also realized that further improvements in the analysis are possible through improvements and refinements to the experimental methods used in obtaining the necessary inputs for the analysis. </p> / Thesis / Master of Engineering (ME)

Aortic valve replacement (AVR) is the only life-saving treatment for patients with severe symptomatic aortic stenosis. Bioprosthetic valves are used in 90% of AVRs because they do not require lifelong anticoagulation. The major limitation of bioprosthetic valves is their limited durability compared to mechanical valves. In addition, bioprosthetic valves still carry a 2-3% risk of symptomatic valve thrombosis, stroke, and thromboembolism in the first 30 days after implantation, and a 1% annual risk thereafter. The risk of subclinical valve thrombosis is around 10% at 30 days and 25% at 1 year, and prevention of subclinical valve thrombosis is hypothesized to reduce the risk of clinical thrombotic events and perhaps even improve valve durability, although high-quality evidence is lacking. This doctoral thesis comprises 7 chapters of varied methodology that summarize the evidence behind current recommendations for antithrombotic therapy after bioprosthetic AVR, identify evidence gaps, and present the design a randomized trial that aims to address some of these evidence gaps. Chapter 1 introduces each included study with a brief summary. Chapter 2 is a narrative review summarizing guideline recommendation for antithrombotic therapy after bioprosthetic AVR and the evidence upon which they are based. Chapter 3 is an observational study describing antithrombotic prescribing practices in the VISION Cardiac Surgery cohort study. Chapter 4 is a systematic review and network meta-analysis of randomized studies of antithrombotic therapy after transcatheter aortic valve replacement. Chapter 5 is a systematic review and meta-analysis of randomized and observational studies of subclinical valve thrombosis. Chapter 6 presents the design and rationale of a feasibility trial of direct oral anticoagulants versus vitamin K antagonists in patients with a new surgical bioprosthetic AVR and atrial fibrillation. Chapter 7 discusses the implications, limitations, and future avenues of the research presented in this doctoral thesis. / Thesis / Doctor of Philosophy (PhD) / More than 10,000 Canadians require aortic valve replacement each year. Bioprosthetic valves (made out of cow or pig tissue) are often preferred over mechanical valves (made out of metal) because the risk of blood clots forming on the valve or causing a stroke is lower. The disadvantage of bioprosthetic valves is that they can wear out and require re-replacement. The reason why bioprosthetic valves wear out is uncertain, but it may be related to small blood clots on the valve that are only detectable on a CT scan. This doctoral thesis explores the use of blood thinners for patients with bioprosthetic aortic valve replacement. Ideally, blood thinners would be able to prevent blood clots and stroke, and to improve the durability of bioprosthetic valves, without causing too much bleeding. The thesis reviews the available evidence, identifies unanswered questions, and ends with a proposal for a study to generate new data.