Studies of Diamond-like Carbon and Diamond-like Carbon Polymer Hybrid Coatings Deposited with Filtered Pulsed Arc Discharge Method for Biomedical Applications

Hydrogen free diamond-like carbon (DLC) coatings have been the subject of investigation all around the world for the last 30 years. DLC, due to its unique properties such as: chemical inertness, high mechanical hardness, high electrical resistivity combined with a characteristics of a wide band semiconductor, is a very promising material for biomedical, mechanical and electrical applications. One of the major problems in producing of thick high-quality DLC coatings has been the inadequate adhesion of the deposited film to the substrate. This obstacle is finally overcome by depositing an intermediate adhesion layer produced with high energy (>2 keV) carbon plasma before application of a high-quality coating produced with a low energy unit. To the best of our knowledge, this can be achieved (with reasonable yield for industrial purposes) only with the filtered pulsed arc discharge (FPAD) method developed by our group. The properties of DLC coatings prepared with the FPAD method are exceptional: they are high quality (>80% diamond sp3 -bonds), ultra-thick (>200 m) and have excellent adhesion to a substrate. In this thesis a new combination of in situ surface oxide reduction method with FPAD is presented. Novel anti-soiling DLC polymer hybrid coatings (DLC-p-h) can be deposited using a slightly modified FPAD system. Both the coatings and their deposition method are recent innovations invented in our research group. This method makes possible to combine diamond and polymer properties in the resulting coatings. Two novel hybrid coatings have been developed: DLC polytetrafluoroethylene hybrid (DLC-PTFE-h) and DLC polydimethylsiloxane hybrid (DLC-PDMS-h). These hybrid coatings are hard and have exceptional dirt repelling (hydrophobic and oleophobic) properties. Therefore these novel coatings could be used as antifouling and wear resistant coatings to which pathogenic bacteria would adhere less than to conventional biomaterials in biomedical applications. They could be also useful in numerous other applications (e.g. in kitchens, food industry, hospitals, medical equipment and implants). These DLC-p-h coatings are not produced anywhere else in the world. In this thesis bacterial adhesion to DLC was studied under dynamic conditions. Our experiments demonstrated that the bacterial adhesion to DLC was similar to the adhesion to AISI 316L surgical steel commonly used in medical applications. This suggested that DLC coating can be used on implants made from AISI 316L or other materials without increasing the risk of implant-related infections. Adhesion of bacteria and human cells (hMSC, hOB, Saos-2) to our novel DLC-p-h coatings was also studied in this thesis. Bacterial adhesion tests showed a potential application of DLC-PTFE-h coating as a less biofouling surface than DLC, titanium and oxidized silicon surfaces. Cell adhesion studies showed less adhesion on DLC-PDMS-h surfaces than on DLC or titanium surfaces and some of the cells even underwent programmed cell death caused by lack or loss of adhesion. Osteogenic differentiation study on DLC-PDMS-h surface showed impaired or delayed osteogenesis. Cytocompatibility and cytotoxicity tests with human Caco-2 and Saos-2 cells proved that DLC-PTFE-h and DLC-PDMS-h coatings are biocompatible. In summary, these studies suggest that DLC-PTFE-h coatings could be used in medical applications where bone integration would be preferred while DLC-PDMS-h coating in orthopedic applications where an implant or implant-facet should be protected against bone overgrowth.