UV Sterilization Effects and Osteoblast Proliferation on Amorphous Carbon Films Classified Based on Optical Constants

Optical classification methods that distinguish amorphous carbon films into six types based on refractive index and extinction coefficient have garnered increasing attention. In this study, five types of amorphous carbon films were prepared on Si substrates using different plasma processes, including physical and chemical vapor deposition. The refractive index and extinction coefficient of the amorphous carbon films were measured using spectroscopic ellipsometry, and the samples were classified into five amorphous carbon types-amorphous, hydrogenated amorphous, tetrahedral amorphous, polymer-like, and graphite-like carbon-based on optical constants. Each amorphous carbon type was irradiated with 253.7 nm UV treatment; the structure and surface properties of each were investigated before and after UV treatment. No significant changes were observed in film structure nor surface oxidation after UV sterilization progressed at approximately the same level for all amorphous carbon types. Osteoblast proliferation associated with amorphous carbon types was evaluated in vitro. Graphite-like carbon, which has relatively high surface oxidation levels, was associated with higher osteoblast proliferation levels than the other carbon types. Our findings inform the selection of suitable amorphous carbon types based on optical constants for use in specific medical devices related to osteoblasts, such as artificial joints and dental implants.