Although graphitic carbon has been known and used as a biomaterial for a very long time, the excellent biocompatibility of diamond-like carbon (DLC) films has been addressed only in a few cases. We anticipate the combination of bioinert DLC films and surface-immobilized bioactive biomolecules with antithrombogenic properties, such as the polysaccharide heparin, as a straightforward concept to optimize the haemocompatibility of a wide variety of materials. Therefore, to assess this property in view of an application as vascular grafts, surface analytical studies on DLC-coated and heparinized polymer and silicon substrates were performed. The DLC films were deposited on polytetrafluoroethylene (PTFE), PTFE vascular prostheses, polystyrene and silicon wafers by an energetic acetylene plasma beam and subsequently exposed to an ammonia plasma before heparin was covalently coupled to such functionalized surfaces by an end-point attachment method. The biochemical characterization by thrombin tests revealed, in accordance with XPS measurements, a high amount of heparin on the surface and an extended blood coagulation time. Thus, the efficiency of the plasma treatment for functionalization and successful improvement of the haemocompatibility of DLC films could be shown. Figure 5. Thrombin activity of various DLC-coated and heparinized substrate materials in dependence on the exposure time in an ammonia plasma beam prior to heparin immobilization. In comparison to the pure and DLC-coated substrates, including the control material (a commercial PTFE vascular graft), an enhanced antithrombogenic activity can be observed for exposure times >30 s.

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Although graphitic carbon has been known and used as a biomaterial for a very long time, the excellent biocompatibility of diamond-like carbon (DLC) films has been addressed only in a few cases. We anticipate the combination of bioinert DLC films and surface-immobilized bioactive biomolecules with antithrombogenic properties, such as the polysaccharide heparin, as a straightforward concept to optimize the haemocompatibility of a wide variety of materials. Therefore, to assess this property in view of an application as vascular grafts, surface analytical studies on DLC-coated and heparinized polymer and silicon substrates were performed. The DLC films were deposited on polytetrafluoroethylene (PTFE), PTFE vascular prostheses, polystyrene and silicon wafers by an energetic acetylene plasma beam and subsequently exposed to an ammonia plasma before heparin was covalently coupled to such functionalized surfaces by an end-point attachment method. The biochemical characterization by thrombin tests revealed, in accordance with XPS measurements, a high amount of heparin on the surface and an extended blood coagulation time. Thus, the efficiency of the plasma treatment for functionalization and successful improvement of the haemocompatibility of DLC films could be shown.

Submillimeter wave gas lasers are characterized by low Fresnel numbers and by gain widths smaller than the mode separations. This allows interferometry of laser emissions and resonator modes with the aid of the laser resonator. The theory of Bergstein and Schachter on modes occurring in resonators with low Fresnel numbers is compared with the experimental data obtained by laser resonator interferometry. The influence of the tilt of a resonator mirror on the intensity of the laser emission is measured for different modes.

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