Structure and properties of annealed amorphous hydrogenated carbon (a-C:H) films for biomedical applications

When a biomaterial comes in contact with a biological body, biological substance denaturation will be concomitant with the physical interaction between the biomaterial surface and biological substance, such as blood protein denaturation resulting from electrical charge transfer. In this study, we investigated the relationship between the physical properties of amorphous hydrogenated carbon (a-C:H) and its blood compatibility. The films were fabricated using plasma immersion ion implantation-deposition (PIII-D), followed by annealing in vacuum between 200 and 600 °C. A series of a-C:H films with different structures and chemical bonds were characterized by Raman, elastic recoil detection (ERD) and atomic force microscopy (AFM). The results indicate that hydrogen effusion and film graphitization are promoted at high annealing temperature. The physical properties and surface characteristics of the films including the carrier concentration and mobility, resistivity, band gap and surface wettability were also examined. Their changes with anneal temperature are due to the increase of sp2 bonding cluster caused by graphitization. The thrombogenesis of the films was evaluated employing in vitro platelet adhesion tests. The adhesion, activation, and morphology of the platelets were investigated using scanning electron microscopy (SEM). The results were correlated with the biological data to elucidate the blood compatibility mechanism of a-C:H films. The platelet adhesion and activation of a-C:H is affected by annealing. It is believed that the possible factors affecting blood compatibility are the adhesion energy of blood plasma, band gap, carrier type and concentration. Improving the electronic structure of a-C:H films is critical to the abatement of platelet activation.