Partner und Internationale Organisationen
(Englisch)
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A, B, CZ, F, D, IRL, I, LT, NL, PL, P, RO, E, CH, TR, GB
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Abstract
(Englisch)
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For implanted or external devices which encounter human blood (such as perfusion devices, columns for treating blood externally, indwelling artificial vascular grafts, and vascular shunts), polymer materials offer excellent mechanical properties and reasonable biocompatibility. However, in some biomedical applications the use of polymers is limited due to inappropriate surface-induced activation of the immune and blood coagulation systems and may result in serious acute and chronic reactions. To overcome these drawbacks, there is a growing interest in surface modification techniques by means of applying functionalized layers. A promising method to achieve this objective is the use of plasma assisted polymerization and deposition of functional layers. This approach is followed in this project. Two different coating techniques were used to generate the appropriate functional layers on the surface of the polymer substrates. All coatings were analyzed and tested with respect to mechanical, electrical, chemical, and biomedical properties. Blood compatibility evaluation is done with in vitro techniques using commercially available test kits for the investigation of surface induced activation of the clotting and the inflammatory systems. The first modifications were plasma deposited diamond-like carbon (DLC) and silicon carbide coatings of Si-wafer and medical grade silicon rubber. Human blood was used for the assessment of the hemocompatibility based on the observation of platelet adhesion and activation, thrombin generation, and complement convertase production induced by the sample surface. Furthermore, the electronic properties in terms of surface potential and work function were determined on a nanometer scale. For this, electrostatic force microscopy (EFM; a new operation mode of the atomic force microscope) was implemented. The ubiquity of the vascular system in the living organism as well as the central role of the Endothelial cell (EC) lining in the processes of inflammation and healing response, are bringing EC pathobiology into focus of the biomaterial research. Since the original publication in 1973 on the techniques of cultivating human EC in vitro, the application of tissue culture methods to various types of endothelial cells has transformed the scientists view of the endothelium from that of a passive barrier between the blood and the vessel wall to that of a highly dynamic tissue with pathogenic relevance for regulating the inflammatory response and the hemostasis. Cell-seeding technologies are amongst the most promising methods, to create a biomimetic micro-environment of the endothelium and to improve the bio-functionality of vascular prostheses. However, due to the fact that the vascular prostheses materials are relatively inert to cell attachment, surface modification steps must be performed to achieve an EC pre-seeding. In this project, cell-binding oligopeptides, recognized by integrins in the EC membrane, will be immobilized on polymer surfaces by plasma activation, and the resulting blood compatibility evaluated as described above. This project was divided into two parts. The first part was to establish methods for the coating of polymer substrates with semi-conducting films and to apply a suitable testing of the resulting blood-compatibility. Furthermore, we developed methods to characterize the surface charge and work-function of these thin films and correlated the measure with the results of the blood tests. The second part of the project was to build a new system for plasma assisted grafting of selected peptide sequences, favorable of epithelial cell attachment. Thin semi-conducting film production was done in collaboration with Dr. J. Krumeich at Sulzer Innotec AG, while all blood tests were done in collaboration with Dr. P. François at Geneva University Hospital. Diamond-Like Carbon (DLC) and Silicon Carbide (SiC) coatings are attractive for the low friction coefficient, high hardness, chemical inertness and smooth surface finish they provide to biomedical devices. When silicone rubber was coated with DLC by the newly developed metal free method using Plasma Vapor Deposition (PVD) techniques, we observed a prolonged clotting time and a lower activation of platelet and complement convertase. This correlated with a higher work-function and lowering of surface localized electrical charges, supposed to be partly responsible for protein denaturalization on implant surfaces. Polypeptides were successfully grafted in a multi-step procedure using a newly developed plasma system for grafting of active amide groups on a polyurethane. The successful grafting was shown by XPS characterization and endothelial cell cultures. Blood clotting and platelet and complement activation on the endothelialized substrates were observed to be significantly lower than on non-endothelialized substrates.
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