oa The Way to a New Generation of Bio-Prostheses

Diseases of heart valves often make a prosthetic replacement therapy necessary. Long term goal is the development of artificial leaflet material with defining properties of mechanical prostheses (i.e. durability) with complete biocompatibility without the need for any anticoagulation therapy whatsoever. In order to achieve this aim, objective efforts are being made to use a new material that is still in the process of development. It is a film-like tissue, made of pure carbon in the form of carbon-nanotubes, which are characterized by their excellent mechanical properties (tensile strength 65GPa in comparison to steel with 0.6Gpa). The woven material has also a very small mesh width, which can be influenced by the spinning method. Due to the nature of this material, which is associated with a high surface energy, there is a need for adaptions for the use in vivo according to the requirements. Plasma Enhanced Chemical Vapor Deposition PECVD has proven to be the appropriate method for such a functionalization. It is possible to deposit amorphous hydrocarbon coatings below 60°C and in a thickness range from a few nanometers up to several microns, while at the same time providing a very low Young's modulus that ensures to withstand mechanical stress. In addition, this method allows to influence regional properties e.g. by incorporating silicon into the matrix to prevent adhesion of thrombocytes and/or to add nitrogen to give the ability to endothelial cell growing. The first project step is to evaluate in high resolution and accuracy the parameter characteristic of native valves and prostheses. Therefore the elastic modulus, flexibility, extension, expansion, banding stress, banding elasticity, banding rigidity, reversed banding strength, cantilever load, surface tension, surface structure, surface tension and intensity of surface loading are under investigation. A mix of physical, chemical and visual analysis methods are used. The parameter characteristic of the nanotube material has to match these results. In cases of mismatch a technical adjustment, e.g. during weaving or coating, is possible. At least two big advantages of this new composite material exist: The possibility to produce a compound material with regional different main characteristics by using a two-phase coating process. And on the other hand the abandonment of exogenous substances during the production process and so the material has a distinct advantage over those currently used Teflon fabrics.