Konzipierung und Validierung einer Polymer-Keramik-Lagerung für eine zweiflügelige mechanische Herzklappenprothese

摘要

Implantation of artificial valves is a safe and routine clinical procedure since more than 30 years and leads to an increased quality of life and life expectancy compared to untreated patients. Worldwide approximately 225.000 artificial heart valves are implanted annually. Nowadays implanted artificial valves can be classified into bioprosthesic and mechanical valves whereas the number of implanted mechanical valves exceeds the number of implanted bioprostheses. Since its introduction into the market in 1969 isotropic pyrolytic carbon is the material of choice for mechanical heart valve prostheses. Currently, 95% of all implanted mechanical heart valve prostheses consist completely or at least partially out of Pyrolytic Carbon. Advantages of pyrolytic carbon are a high wear resistance leading to a high long term durability of mechanical valves, normally enduring a recipient's lifetime. Through the usage of synthetic materials a high reproducibility of the manufacturing is enabled. Main disadvantages are the need for a lifelong anticoagulation associated with risk of bleeding and an extensive manufacturing process and thus high manufacturing costs for mechanical heart valves. The present work describes a concept for the development of a mechanical heart valve prosthesis made of polymeric materials with a hinge design which enables the integration of ceramic materials in the leaflets. Additionally the mechanical heart valve offers an improved flow path compared to commercially available ones. The concept is based on a bileaflet mechanical heart valve. Bileaflet mechanical valves have proven their function in clinical applications and the application normally increases the life expectancy and quality of life of patients. Material properties of considered materials are compared to choose the most suitable material. The final material selection is supported by the results of a wear study done in a pin-on-disc tribometer. Next steps were to design the mechanical heart valve prosthesis and especially the development of a hinge design which enables the integration of tribomaterials in the leaflets. First lab types of the heart valve prosthesis were manufactured in a combined turning-milling process by means of CAD-CAM. Validation of the functionality was done in vitro according to the guidelines of the American Food and Drug Administration (FDA) and ISO Standard 5840. The functionality and the durability of the polymer-ceramic hinge design as well as the hydrodynamic properties and cavitation potential of the mechanical heart valve is presented. Results are promising and confirm the concept to develop a mechanical heart valve made of polymeric materials. Finally, the main results are summarized and discussed in context.